Radiators and heat pumps

Radiators and heat pumps

Heat pump energy delivery can be calculated using just 3 parameters. The flow of water passing through the machine and the inlet and output temperatures – that’s all.  Heat pumps deliver energy at lower temperatures than gas or oil boilers so they need to flow more water to contain and transport that energy. That’s why the pipes coming out of a heat pump are fairly large.  When that high flow is confronted by the slightly smaller pipes of a system designed for radiators it can get bogged down, even more so when the house has zoned heating areas and many parts are shut down. For these reasons the heat pump must be able to modulate the output flow – not all can.

The same 3 parameter calculation – flow and temperature drop – works for the heat output of radiators and for that matter, to heated floors. In typical 15mm OD pipes, leading directly off a radiator for example, flow will be around 7 litres/minute  and, when supplied from a gas or oil boiler, at least 65C on the inlet, dropping to say 55C on the outlet (Dt of 10). The power extracted and delivered to the room in this case would be 4.9kW. So very hot radiators work well.

As flow is constrained by pipe size it is the design and size of the radiator that decides how much energy it can transmit and what the resulting Dt is. Heat transmission is restricted by any sludge on the inside and also the insulating boundary layer of air on the outside, just like the slower water flow near the banks of a river. The rate of loss of heat is proportional to the excess temperature of the surroundings, so clearly hotter radiators work best and also benefit from a stronger updraught which strips the heat off.

If we lower the temperature range to say 45 in, 35 out (typical heat pump) the calculation for power delivery would remain the same (Dt of 10 again) but the temperature drop is harder to achieve as the lower differential to the room cuts the updraught and also the heat transfer. The result can be a disastrous drop in performance – more than half. Your shiny new heat pump might have the nominal power output but the rads just can’t shift it to the rooms.

Assuming you are not able to dig up your floors for under-floor heating the solution is to blow air over the radiator surface to shift that boundary layer and replace it with cool air at room temperature, just like blowing on a hot cup of tea. That’s what fan-coil units do – they are fan assisted radiators and with their lower operating temperature they can make a heat pump system actually work.

Reverting back to our power calculation the other parameter is flow, so turning up the heating circulation pump speed is worth a try although pipe size imposes limits on this. Of course increasing pipe size is an often suggested solution and the right one if micro-bore pipes are in use. However my model suggests that the normal 15mm pipes will do as long as the delta T can be reached.

Quite often the main feed will be in 22mm pipe with 15mm take offs to the radiators. So just one pipe feeds all the radiators from your main heat source. This can easily flow about 14 litres/minute which with a 10 degrees Dt produces 9.8kW. The choice of power output of the heat pump is limited by the pipes it serves. Don’t buy a huge expensive heat pump because it won’t make any difference.

Of course if two or more pipes can be fed in parallel from the source then all these flow issues disappear.

Theoretically some heat pumps can deliver 60 degree temperatures but it is a struggle, particularly in very cold weather, and will result in a COP near to 2.5.  Running costs will be worse than town gas. Fitting fan-coils will lift the COP to about 3 and give much better performance all round. The order of play should be to get the heat pump installed then start fitting fan-coil units and turning down the set point as you go. Check out here for an inexpensive DIY fan-coil unit  (pictured)

DIY fan-coil unit

At this point you might be dismayed to realise that your house needs more energy than your pipes and radiators can transmit. Don’t despair though. Have a think about installing a mini-split as well. These are independent, air to air heat pump units, quite cheap and they can do air conditioning as well as make heat. They make excellent partners with PV panels which apart from running your heat pump in the winter will have masses of surplus power in the summer to run air conditioning.

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Property crash coming soon

Death, Debt and Demography – property peril

UK going ex-growth

If everybody in the U.K. was made to stand in line according to age they would make a giant bar graph like this. Your place is there too; as you grow older each year your own line takes a sideways step to the right, and so does everyone else’s.

The steep ramp down to zero starts earlier than you would expect, from as young as the mid fifties. This is due to population growth (fewer people were born in the past so the corresponding lines are smaller) and also early death. You don’t have to wait for old age to join the 542,000 deaths each year; over 300,000 die from cancer, dementia, heart and stroke, all of which can strike prematurely.

The chart illustrates how demand from an ever increasing population made the meteoric rise in house prices inevitable. Look at the biggest and tallest block on the chart – the sixties baby boomers. The biggest population surge ever seen, grew up, got jobs and bought houses as fast as they could be built. Easy access to cheap money accompanied the latter days of the surge so it was inevitable that the run in prices would continue into territory that now looks uncomfortably overbought. That is just the nature of markets.

Once the rush started a new ‘truth’ emerged. With prices perpetually rising, for many borrowers there was no question of repaying their interest only loans; they could always sell at a profit, pay off the debt, buy a car and live happily ever after. This sort of thinking actually worked when prices kept rising; even the lenders got sucked in as their loans appeared to be safe. Old habits die hard it seems but what happens to those loans in a stagnant or falling market? Debt is a deferred payment which has to be paid by someone. Could it be that current buyers are not fully aware that they will have to pay back every penny? Now those mad days are over some recent house purchases may never be paid for, much to the chagrin of the lenders. An unfortunate knock-on from this mistaken optimism is that it inevitably depletes the inheritance tally of the next generation and their ability to buy a house.

Today the bulk of the boomers are middle aged, employed and at the height of their earning power, they mostly bought their houses cheaply and have seen their equity rise enough to borrow against it. There is a smart car on the driveway (brand new for one in ten households), holidays, restaurants, life is good. The bounty doesn’t stop there though, their parents are dying, a house is inherited to be sold or rented out. If only life could be so easy for everyone. The chart says no.

After the peak of the boomers the birth rate started to decline, 13 years in a row, and that signaled the end of their powerful influence on property prices and a lot more besides. The big arrow on the left of the chart shows the annual birth tally in gentle decline for the last 50 years. For now, births still exceed deaths so the population is still growing but births initially make more expense for the very group that is already struggling with high house prices.

The arrival of the baby boomers caused some seismic but positive effects and now, as they start to retire, we can expect to see some negativity as those effects are reversed. More people will retire for each of the next fourteen years until half the current block of baby boomers is drawing pensions with the other half still to go. From 2020 on, retirees start to overwhelm the young earners (backward slope in their area) coming up behind them.

The chart has an even bigger story to tell. Note the two big arrows on the chart and the abrupt change in direction just where the baby boomers peak occurs some 50 years ago. This is a momentous event not seen before for centuries; it signals the end of population growth and the start of a new ex-growth era. The effects of this will be profound, affecting pensions, business, stock valuations and more. As the change takes place the money – that washed plentifully over industries like travel, baby goods, retail, house builders and automotive – is drying up, with results that have recently been all too obvious. Sector by sector is succumbing to a lack of cash. The change is well under way with a lot more to come. House prices will be next. Ironically, as the wealthy baby boomers decrease their spending the resulting job loses are born by the next generation and job uncertainty holds back house buying decisions.

The Government will have to fund all the extra draws on the NHS, pensions, debt funding etc. by increasing taxes or borrowing more. But with the number of tax payers declining the Government will have to sell more bonds and this at a time when pension funds become net sellers of bonds (to pay out the pensions of course). With fewer buyers for bonds the only way to make them more attractive is to raise yields and this devalues existing bonds so even more have to be sold to pay the pensions. This is just one example of how ex-growth U.K. faces some intractable vicious circles. The point though is that this puts upward pressure on interest rates. The bank base rate is now 0.75% so there is very little scope for a fall so when change does come it is likely to be bad for property prices.

Excess personal debt is a major threat to property prices. On the surface daily life looks normal and secure but in reality it’s artificially and precariously propped by debt. We’re flying by pulling on our bootlaces. Whether through poverty or imagined wellbeing, personal debt continues to grow. Average household credit card debt is now £2,603 – pretty astonishing for the average. It seems unlikely that anyone needing this much debt can pay it back very quickly and it is predicted that the figure will increase substantially in the next 4 years. Average adult debt for everything including mortgages is £59,823. With record debt there is hardly a wall of money heading towards the property market.

Then there is government debt. As the retirees swell to well over 17 million that produces an annual pensions demand of around £170 billion not including the extra demand on the health service. The pensions industry and the Government need to be ready for this. The former already have their prudence being tested (or exposed) by the ex growth phenomenon but the problem for the Government is more acute. Pensions have always been met by the expanding set of workers following behind; a system that always worked when earners were growing in number. After centuries of habit forming complacency that era is now over. The new paradigm must involve extra taxes and borrowing. In contrast to the private pension system there is no Government pension pot, just borrowings of over £1,800,000,000,000 which is £56,000 per taxpayer and nearer £75,000 when future pension obligations are added (a promise to pay in the future is a debt). With talk of ‘fiscal headroom’ and post Brexit expenses looming these totals will certainly increase. There is talk about the end of posterity but that’s a word we can expect to see again.

The property boom has divided society into two halves. The people on the right half of the chart live in houses bought cheaply and they are very well off. All the people on the left don’t have a house and can only ever buy an expensive one; after rent, rates, general living expenses these are the people with credit card debts instead of savings.

Take the younger group shown in grey; they are starting out on their careers with little chance of buying a house of their own except via inheritance or parental gifts. The national house price to earnings ratio might be at a peaky 6 but that’s an average. Take a typical cookie cutter house in the south of England for £450,000 and the average wage of £26,364 and the ratio is 17; totally unsustainable, especially as hopeful buyers trapped in expensive rental properties are more likely to be in debt rather than building a savings pot. Let’s be clear about house price to earnings ratios; if the ratio is 17 then it would take ALL your earnings over 17 years to pay for it, and that’s before interest. Potential buyers for houses at the current prices are not in this grey group.

Obviously there are buyers out there, not very many though and declining by the year, but there non-the-less. In the home counties in particular properties are being bought by new millionaire Londoners cashing in before prices retreat further.

And buying still makes sense right? The agents saw high demand for these high priced houses which were sold quickly too – business was booming. Hold on, hold on; that’s the first danger sign slipping by – high turnover. Turnover so high that your local high street can support several estate agents (but no banks) – something weird there. When there are too many buyers or too many sellers there is an imbalance and transactions are relatively low. When there is a transition from one state to another there is a period when sellers exactly match the buyers; perfect conditions for a peak in transactions and peak agents. Logically, when transaction volume is high the market is turning. What looks like a buying frenzy is actually a subtle warning sign. The bubble is about to burst. Is that now? The house builders, are no longer making hay – maybe change is in the air?

A market correction has never amounted to much before and setbacks have always been ironed out over time. You can’t go wrong in bricks and mortar can you? Well things might be different this time. At this point we hear the call ‘there is a massive property shortage so prices can’t possibly fall’. Actually there is a shortage of ‘affordable’ property, but there is no shortage at all of ridiculously expensive properties, the market is flooded with them. You might note how half of them have price reductions; they are not exactly being snapped up.

It would be no surprise if Brexit goes down in history as the trigger that turned the property market and burst some other bubbles too.  The transition will certainly be disruptive in the short term. There are thousands of areas where there will be a threat to jobs and in turn a threat to property prices.

Watch the pound carefully while Brexit unravels. Any need to defend a weak currency could raise interest rates and that will make holding or buying property even more expensive. Actually it makes everything more expensive; a country with a huge debt burden can only expect huge interest burdens when rates rise.

It can’t be sensible to be invested in an overvalued asset class while all this is going on. Buy-to-let investors (already taxed and stamped) are reasonably liquid and might well see the sense in locking in profits right now. Any obvious downturn in the market will set them selling and after that most buyers will step back to watch the fall.

So, to summarise; property prices are unsustainably high, the money that bought them was easy and cheap but is now evaporating. The ex-growth G.B. effect has kicked in disturbingly early with still more jobs at risk. The market may be turning now, or very soon, and when it does the fall will be sudden and without respite. Bubbles don’t burst quietly.

Follow up March 2020:   Well there we are; the pin to burst the bubble has arrived and all sorts of unexpected consequences are popping up. One yet to be seen is the effect on the lenders as their clients lose their jobs and maybe even their lives. In short they have lent on overpriced collateral to clients who can’t pay them back. A black hole in the accounts will decrease the funds to be lent. If turning off the money tap doesn’t trouble the property market I’d be very surprised.

Heating system for heat pump – 2020 revision

As you might have read in the last Heating News, cheap PV panels have radically changed a few of our preconceptions about heating. The heating system layout has become much simpler (and less expensive) as under-floor heating and wet solar panels are deleted and heat pump connections are simplified.

heating system for heat pump

heat pump – heating and cooling

The heat pump connections are easier thanks to the Original Twist Hybrid Heat Pump which indirectly supplies chilled water without breaking the rules for the RHI incentives. Note that the system copes with 2 set points from the heat pump; hot water is routed to the hot tank while the heating is kept going with stored energy from the cooler tank. For a lower set point heat is sent directly to the heating side without disrupting the stratification in the tank. The system can heat either tank while simultaneously supplying chilled air – how cool is that? An extra immersion heater helps use all that extra PV energy, useful now that FITs are trivial.

You can see the original system here along with a long list of all the benefits which still make this the best system on the planet.

You might have sussed that with 2 tanks here and 2 from the heat pump system your tech room is going to be large and, dare I say, impressive. I imagine all the tanks raised slightly on a low wall with wooden slats across the top. This allows most of the pipes to be hidden. The tanks are often raised when a wood burning stove is connected and gravity circulation is required.

What’s the point? Well it’s all about integration of multiple input sources, like a wood burning stove or a gas boiler along with a heat pump. Many experts say you can’t integrate all these things but they are wrong.

Heating News Autumn 2019 – Extinction Solutions edition

Heating News Autumn 2019

Extinction solutions

Rebelling is OK; better to actually do something.

So we could save the planet could we? Well yes, we could certainly do our bit in a big way. Recent advances in solar technology mean our homes can be made self sufficient in energy and leave us better off financially at the same time. The off-grid theme is all electric, quite simple and more DIYable too if that’s your thing. About 20 panels, a heat pump, some tanks of water and we are pretty much there. We can’t ignore an electric car, even though depreciation is going to slay us, so that could be in the mix too. So let’s chat about some of the issues that arise.

 

DIY power – cheaper than nuclear?

In the EU nuclear power costs $5,500 per kilowatt of capacity (each Kw producing 8,760kW.hrs a year). We pay that cost via our taxes and then pay again to buy that power. Put that way it sounds a bit perverse; could there be an alternative? A domestic PV array with battery storage could make almost as much energy for the same money and, as the owner pays for it, there is zero cost to the government. Could a mass take up of home energy production do away with a power station? Take the $10bn cost of a new nuclear power plant and instead give it to the 1.5m customers it would service and you’d have a subsidy of over $6,000 per person. You could twist a lot more than 1.5m arms with that sort of money yet the government has just ceased to pay feed in tariffs!

 

Heat pumps and the Renewable Heat Incentive

The RHI on a ground source heat pump is a government bung, to you, of something like £20,000 – £30,000 over 7 years. That’s high because a GSHP is expensive; but what if it wasn’t? The Original Twist hybrid GSHP concept (with air assistance) makes everything cheaper and more efficient. And by cheaper we’re looking to go well below that RHI contribution so your project cost is easily nil and beyond. It is all explained here.

 

Photovoltaic panel prices and power.

overclock and tilt PV panels

PV overclock and tilt

The power of new PV panels is increasing by the month. 350W, even 400W (at a price) is possible now.

As power rises the cost keeps falling quite noticeably. My old 4.6kW car port roof, – 20 panels – would now be good for 6.1kW and under £3,300 with some 305W Jinko Smart Solar Panels. The latter are not particularly cheap but they limit their own output voltage which makes inverter choices easier and helps with the overclock and tilt concept.

 

Feed In Tariffs – a new paradigm

It was all doom and gloom last March as the government FITs came to an end. Presumably PV kit had become cheap enough to make us self incentivised without a nudge from the government. You might remember, in the last newsletter, I pointed out that prices had fallen significantly, grid parity had arrived making off grid a viable option.

However, FITs have revived in an interesting way. With Octopus leading the way, the energy providers will be introducing their own FITs. ‘Outgoing Octopus’ is a plan which works alongside a smart energy meter and if you have energy to sell, from any source, they’ll give you 5.5p/kW.hr and it gets added to your account with them. Unfortunately for an 8kW PV system running a heat pump etc you’d be lucky to sell enough surplus to bag more than £200 a year but a grid connected system would not need any expensive batteries so you can get going at a much lower cost.

‘Octopus Agile’ is another offering which charges and/or pays you according to half hour market rates, typically between 4p and 10p.  Even negative rates can occur where you would actually be paid to take in power. With some fancy software and a hook up to the car batteries we could all be future energy traders but, that aside, I think the off grid brigade will be going with this one.

Octopus Go. Charge your electric car for just 5p/kW.hr for four hours a night. This is better than trying to charge your car with your off-grid arrangement. It’s just not sensible to charge your house batteries during the day in order to charge the car by night. That would be an expensive heavy duty battery hammering. So going completely off grid is probably not for electric car owners. That 5p looks very attractive especially when combined with a little night-timed appliance and heat pump running, so we’ll consider below how to add it to an off-grid set up. You can’t combine this deal with Octopus FITs deals.

 

How to be off-grid but still connected.

OK, you have the car charging deal so you have access to the grid. You can’t sell to the grid so the flow can only be incoming. With that in mind you want an off grid set up – panels and batteries – with no two way connection to the mains. For a solution there is just one and only type of link – the mains can run a battery charger and charge the house batteries but they can’t return the flow. Similarly the mains is connected to the car battery charger. The net result is:

The car gets charged at 5p/kW.hr

Timed appliances and the heat pump can run cheaply at night if they need to

The house system is off-grid but has mains back up

A less mission critical off-grid system can be smaller and cheaper.

If all the panels get snowed up for a few days it doesn’t matter.

The lights stay on if there is a power cut.

 

Solar thermal panels are obsolete?

Why no mentions of the wet panels?  Well PV is relatively cheap now so it is easier to just add more electric power rather than get involved with a more complicated installation. In weak winter sun wet panels don’t do much especially when the water tank is already hot. In summer there is enough excess PV solar power to run an immersion heater so, again, we don’t need the wet panels. That’s a big expense to cross off the list. Paradoxically you can get RHI payments on wet panels but not on PV – the government backing the wrong horse again?

 

Underfloor heating is obsolete?

Good insulation makes UFH an unnecessary waste of thousands of pounds. Fan-coils (basically a radiator with a fan on it) make more sense and can cost very little. Here’s the Original Twist DIY fan-coil which is arguably better than a tailor made one. This change of tactic alone could fund your off-grid move.

 

Gas is obsolete?

The Chancellor Philip Hammond has announced that gas heating will be banned for new build homes by 2025. A seemingly innocuous announcement but what it means is that the most used energy source (costing a quarter as much as electricity) will gradually be removed from our future heating choices. Apart from adding massive insulation the only way to restore reasonable expenditure is to drive a heat pump with electricity and we can expect to see a lot more of them from now on. The RHI payment on heat pumps will inevitably subside when they become practically mandatory so have a good think about locking into that now. Once boilers go, gas hobs and ovens will follow them into obscurity; there is no point in paying daily supply charges for minimal use when electric hobs and ovens are arguably better anyway.

Conclusion

It’s interesting to see the knock-on effects of falling PV prices and to react appropriately with the right heating/energy strategy. The all electric home looks much simpler and cheaper as a result. The bottom line is that going off grid saves you money, the government will pay for most of it anyway, and you can do your bit to save the world.

Air AND Ground Heat Pump hybrid

Hybrid Heat pump by Original Twist

Combined air and ground source

Heat pumps of all sorts (ground source or air source) are going to save the World. The debate over ground or air rages on but is largely irrelevant when a hybrid design could cherry pick the best bits from both. Both suck heat out their surroundings and pump it to a higher level.  You get 3 or 4 times more energy out than is put in, a seemingly impossible engineering miracle which still, for many, defies belief. The in-out energy ratio is the coefficient of performance or COP.

First lets join the debate about ASHP vs GSHP by comparing the COPs of both across the season.

The ASHP operates in a wide temperature range between the red line (day time running) and the blue line (night time running). Cold night time temperatures look pretty disastrous but warmer day time running produces consistently high COPs. On the black line the GSHP does without the wild swings and gently declines in performance as it sucks the heat out of the ever cooling ground.

showing the COP difference between ASHP and GSHP

Day COP vs. Night COP

While the GSHP (black line) gradually loses performance over the winter the ASHP can always do better on warmer days (red line) making the two systems closely matched during the daytime, up until Christmas anyway. Soon after that the daytime COP on the air source starts to improve while the ground source continues to deteriorate.  The only redeeming feature of the ground source is that it is miles better than the air source blue line at night and cold days.

Even though the GSHP rules the night an ASHP system geared towards more daytime running would be a match for the much more expensive GSHP which, let’s face it, doesn’t always need to run at night at all.

However, some new electricity deals for electric car charging (7.5p/kW.hr at night – April 2022) make a GSHP, with more night time running, quite compelling. It might be thermally less efficient but the running cost is only 25% that of daytime rates.

If only there was a system that could cherry pick the best COP line on the chart for any given moment. It would need to extract heat from the air on most days – red line – and extract heat from the ground at night – black line. The air side would not run at night so the blue line can be ignored and the system would cherry pick between the red and black lines. The average COP over the season would be around 4 which is better than either system on its own, so best in the world then. Luckily designing such a system is easy really and not particularly expensive either.

 Original Twist Hybrid heat pump.

GSHP unit

For the core of the system we start with a GSHP unit.  As the name implies we need to feed it with some warmed water from a ground loop or slinky and more on that later.

Air source module

There is already water going in and out of the GSHP unit so warming it with air is simple. Just connect a parallel circuit incorporating an air handler unit, that is to say, a large heat exchanger with a fan on it. This is only connected to the buffer tank and is completely independent.

A few car radiators (surprisingly cheap) and a fan or two to make the equivalent of an air handler for about £200. 12v fans for cars are waterproof and easily available. A simple solar controller brings in the AS module whenever it can contribute.

Buffer tank

A buffer tank is used to handle the cold water coming out of the heat pump. The tank allows the air side to store daytime energy.

Warm air is a great resource so we decouple the air source module and let it run whenever there is a benefit, whether the heat pump is on or not. The tank will nearly always be available to charge when the heat pump is running and supplying an icy return flow on its way to the slinkys.  A solar controller turns on the fans and the circulation pump. Similarly a Dt controller optimally switches the valve which chooses between the flow from the tank to the slinkys or direct flow to the heat pump. The valve needs to be a Coster valve which gives a blended changeover rather than a paused switch otherwise the heat pump might get confused. When the tank is warmed up the flow back into the slinkys is highly beneficial by raising the COP line slightly and delaying that end of season fall off in performance. The straight black line on the COP chart will bend upwards into better COP territory as shown in the new chart.  The new system always selects the best source for the best COP  and  is  always  superior  to  conventional  systems.

 

 

Slinky coil

Normally the ground starts the winter at around 12C then the GSHP and cold weather gradually take that down to around 0C. Permafrost around slinkys is not unusual. Normal ground loops are designed to perform at the worst end of this so they have to be huge. Not so with ours which can be very much smaller because:-

  • The ground starts the winter overcharged. We dump heat into it in the summer.
  • Frequent recharging takes place.
  • The cold return is usually pre-warmed by the air side before going back to the ground.
  • Day time running of the GSHP is less frequent so the ground temperature can recover better.
  • Towards the end of winter, as the air warms up, the Air Source Module takes on practically all the load. The end of season performance stress on the slinky is avoided so the design is less critical and it can be considerably smaller.

I’ve done a job where the slinky was trucked down from Switzerland along with a man in a white coat and a bill for thousands; a bit over the top when polyethylene tube from the local builders merchant is just as good and costs under £300.

N.B. The pipes are filled with antifreeze and there are regulations about ground pollution so you can’t be too casual about pipe specification.

The RHI payments have stopped and the incentive is £5,000 for an ASHP and £6,000 for a GSHP.

Pipes for the air side and the slinkys

It’s important to note that the power eventually delivered by the heat pump has to come from the air side or the slinky or both together. A quick look at my model for power and flow shows that for the air side the pipes will have to be 1″ at least to flow enough to raise 10kW on a Dt of 6 degrees. Same goes for the slinkys where on the same parameters the water would be in one pipe for around 2 minutes so it would almost certainly be better to have 2 slinkys in parallel to make that 4 minutes. A rule of thumb is that 10m of slinky trench makes 1kW so 100m for 10kW. Could we halve that ?  Maybe not quite but there would be no stress in cutting down a lot. Don’t forget that most of the time the air side and the slinky would run together so reaching 10kW would not be a problem.

Solar powerhouse.

Just a thought. If all this kit were built into a small shed with sun facing glass sides it would be easy to fit the fans into the back wall and the heat pump onto a shelf for easy access. The solar input would raise the COP slightly and a few black water containers would store heat to ward off radiator frosting. To go even further, the air side could be boosted by big ground heated tubes which typically are good for a lift of 5 degrees. There would be wooden slatted duck boards on the floor to let the air up. So, with all this, not just best in the world but best of the best in the world.

Air conditioning

In the summer the cold tank can be left to get really cold and a coil can send the cold to the main heating system and onwards to the fan coil units.  Aircon sorted for almost no cost!

BTW – the heat pump  module will be making heat when the aircon is running so you can heat the pool! Think of the pool heat exchanger as just another radiator on the domestic circuit, it couldn’t be simpler or cheaper.

Summary

So that’s it. Better COPs than a GSHP or an ASHP, aircon, ground loop recharge, smaller ground loops and a better match to PV panels (more day time running).  The smaller ground loop might just swing this for owners of regular sized gardens.

 

ultimate eco heating

Ultimate Eco-heating system

If you are looking at heat pumps then I’ll assume you will have seen this heating system which particularly favours daytime running of Air Source Heat Pumps, a feature in keeping with the free power from PV panels.

In the light of my comments in Heating News this system has been revised and simplified. Revision 2

overclock and tilt PV panels

PV overclock and tilt

Using big PV to go off-grid – or nearly off-grid – makes sense especially when driving a heat pump. You’ll need every trick to make a limited energy supply go further so make sure you check out the 6kW overclock and tilt concept.

 

Light hybrid car transmission

Ultra-Light Hybrid

How far can a hybrid car be pared down to make the lightest, cheapest and simplest runabout?

Well, for a start the batteries should only be enough for the ‘key local services’ trip of under 25 miles; under 5kW.hrs then and under £1,000. And that immediately starts the benign circle of lightness where many components spiral down in weight and cost.

tiny car engine

cheap and light engine

 

The engine – This modified Honda GX270 engine can be picked up with one hand but still delivers 12hp, just like Fiat 500s and 2CVs of old. The engine connects to one end of a short power shaft via a lockable centrifugal clutch so the electric motor on the other end can start it.

The electric motor: Eg. The 7Kg Magnax motor is the size of a soup bowl and produces a peak boost power of 113hp. Our small batteries will considerably reduce this but even so the power will be adequate, especially if supercaps are used for acceleration. The motor also provides regenerative braking and two reverse gears.

 

 

hybrid car transmission

2 speed gearbox and differential unit

The transmission: From the power shaft two selectable gears drive the differential unit and the drive shafts. N.B. The gears can be replaced with chains and sprockets for a quick DIY version – just side plates without the cast housing.

Why two speeds? Some electric cars just have a single speed direct drive but having a low gear for hill starts and town pottering and a high gear for relaxed cruising is a necessary nod to the limitations of the petrol engine. A simple programmable logic controller matches gearchanges perfectly and more besides.

A cam driven pump on the drive shaft circulates transmission oil to cool the electric motor and the finned case dissipates heat from the returning oil without the need for a radiator.

With regenerative braking there is less cooling needed on the brake discs so they are moved inboard and neatly integrated onto the side plates. The petrol engine and the electric motor have to be spaced off to allow the brake discs to fit beneath them. The effects of this position change to inboard brakes are so profound that brakes are dealt with in more detail later.

The unit is completed by supporting the steering rack and some suspension as well. Super light vehicles need less unsprung weight; this solution is much better than in-wheel motors and brakes.

This tiny integrated unit is all there is to the powertrain. No wonder Silicon Valley, Dyson et al feel they can join the automotive fray – they can. When contracted out a package like this covers most of the engineering work leaving the new entrants to focus on their metier – control and electronic interfaces. Will car buyers want inexpensive light hybrids that run almost free and barely need a service? Maybe, but it’s the new breed of car makers that will first be attracted to this package.

Solar panels – Our low voltage batteries would be compatible with on-car solar panels. Between 200 – 400W trickling in all day is worth something like another 10 miles in the bank which is a huge increase on the standard range. This is only viable on light and low powered cars but makes for good marketing USP.

charging post for electric car

self docking car charger

Auto connect charging – Low voltage and low power enables safe charging like this. Drive up against the spring loaded prongs and the electronics check connections and allocate polarity. A vertical slatted grill on the car completes the connections but still allows air flow. No special accuracy is needed from the driver with last contact automatically controlled; just drive into your car port and press the ‘dock and charge’ button to let the car creep up and connect. An air blast dryer might be needed for wet days – hello Dyson.

 

complex panels made easy

Aluminium panels – Complex light panels can be made with a CNC machined ply and aluminium sandwich. Internal plugs with star washers feed heavy loads into the structure. Suitable for complex bulkheads, doors and in particular for battery boxes. Edges are peened over and ply machined away to leave hidden internal struts. Early Lotus F1 cars used a similar idea for bulkheads.

 

 

tube and mount for torsional rigidity

light but rigid bulkhead connectors

Light aluminium tubes between bulkheads give useful channels and torsional rigidity to the vehicle. The cast aluminium brackets have a slight internal taper at the ends. Tubes are glued then expanded a few thou with a pressed-in taper ring. For production it would be quicker and cheaper to swage (whack em with a hammer) the ends of the tubes.

 

 

Brakes

The day that cars were required to do an emergency stop with no help from our leg muscles was the day hydraulic brakes became redundant. Instead of using ever more complex interfaces with electronics the hydraulics should have been entirely binned.

With inboard brakes it is easier to go all electric with no particular size restraints. For example a 120mm diameter stepper motor driving an internal ball screw could easily push a brake pad onto a floating brake disc. With each twist caliper’ mounted on a pivot, a load sensor can enable braking power to be calculated making these brakes particularly suited to autonomy. Actually, even calipers might be redundant; something more like a clutch assembly allows spring assistance (and a power free parking brake) and less power from the actuator. In other words the brakes are already on by default -like a clutch – and the actuator starts by forcing them off. Either way, all the usual features – EBS, ABS, yaw control, hill descent, handbrake, pad wear check, regen prioritising, LSD – are all easily accommodated.

I write this in frustration at the lack of affordable electric runabouts – likes and comments are welcome.

 

Amazing AirBnb driveable house

It’s a house Jim but not as we know it

Planners usually allow you to build a pod within the curtilage of your house. This one follows the rules but it comes on wheels. So what’s the point of that? Well for a start there are no foundations to worry about, just a bit of hardstanding will do. Then there is the ability to drive it; an all electric 4×4 chassis enables you to go for a trundle, down to the pond to watch the sunset for example. Steering is done from the front or from outside.

With the front wheels turned to full lock the whole house can rotate to track the sun, making full use of the 4.8kW photovoltaic array. So yes, it’s all off grid and only needs to dock occasionally to empty some tanks and to refill others.

Design – To make it all really feasible the design is based on off the shelf parts. So the house part is a modified 20′ shipping container supplied from a specialist constructor. The chassis part is from a 110″ Landrover with all the steering, gearbox and axles – a simple electric motor to drive it (cheap 240V, nothing fancy). Wheels are small and fat from a lawn tractor.

The solar panels are offset to make a canopy over the front porch.

Is it worth all the bother? Absolutely, for rental to eco enthusiasts this is a thrilling bit of kit. Imagine their delight when their pod comes round the corner to pick them up and take them to some lovely spot – all filmed from various points to give them a memento of an amazing experience. You can charge a lot more for that than if you were just offering a shed (I think they call them shepherd’s huts these days)….. is this a self powered off-grid shepherd’s hut then?

If you want to use this on your piece of land you might put a 3-point hitch on the back and call it a tractor – great to sit in a comfy chair while you mow the lawn!

N.B. With proper PV panel dimensions this is a preliminary sketch to see what it might look like.

Part of the drama is the house slowly turning to face the sun 🌻 a few times a day.

12 panels, 4.8kW makes another 14% through tracking the sun so it’s effectively a 5.5Kw array. Makes a useful UPS with it’s batteries. This machine will easily run your heat pump so it’s going to solve your heating problem too – at least an extra £1,000 in your pocket every year from that. Once hooked up to your main house the power can flow either way so the mini-split heater in the driveable house will always be useable, even after prolonged dark winter days.

So, £3,000 worth of electricity, £1,000 heating savings and over £1,000 a week on Airbnb + sales of the book and the experience video. Compare this with a buy to let house and with a build cost of circa £50,000 it doesn’t seem so mad after all. You could get your money back in 2 years and then live off this thing.
Guests are filmed as the house arrives, they get in and drive away to the viewing spot where there is a facilities block along with power and TV hook-up.
 
There’s a nice design for the hook-up to the facilities block. Ask me for details when you build this.
 

 

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Grid Parity – PV goes mainstream

Grid Parity – we’re there – sort of.

Grid parity for Photovoltaics – when PV panels make electricity as cheaply as the grid does. It was inevitable that the lines for falling panel prices and rising energy costs would cross and grow wider apart from then on. On the production side this was reached a while ago; renewables beat power stations. For domestic consumption my definition of real grid parity is when it pays to borrow the money to buy the kit that replaces the mains supply. Well we are there now and the implications of this seemingly innocuous bit of news are profound; we are entering the era when it actually makes sense for some people to ditch their main supplier and go off-grid. The off-grid scene is no longer the province of hippies and eco warriors, it is now yours.

Last year grid parity still looked a way off but there’s been a change. Panel prices have fallen to a level in line with the second hand ones I was on about last year, £105 for 275W for example. And the big event is the arrival of a price busting bit of control electronics.

5kW inverter/charger

All In One Outback Inverter MPPT SPC III combined charge controller and inverter. This controls the charging of the batteries and supplies 240v ac in a computer friendly sine wave. The 5kW version comes in at around £1,000 and enables Bimble solar to offer a full off-grid kit for £4,533.50 with batteries and 14 275W panels (3.85kWp). N.B. Note the rather low input power. While we recently featured a quite useable 1.2kW system, which runs lights and a fridge and the odd extra, this 5kW one will at least spin up some home appliances but compared to the mains its utility is a bit light weight.

Of course parity depends on the price of the electricity being replaced and whether the PV electricity generated is used. Surplus power can be routed to an immersion heater, car charging or aircon so it is possible to have a system where every Watt is banked.

So. Starting with a £5,000 investment for the kit. Sainsburys Bank wants £91.05 a month for 5 years to pay it off. After 5 years you should enjoy free power for another 15 years or so and freedom from rising prices too. This apparent no brainer deal is tempered slightly by the fact that after every 7 – 10 years the batteries will need replacing; the ones on our sample kit from Bimble cost almost £1,000. That sounds a lot although £12 a month put aside has it covered.

 Italy

In expensive but sunny Italy, where a Kw hour costs a third of a Euro, our 14 panels should generate 4,355Kw hours or about €120 worth a month. So yes, in Italy, grid parity has arrived and freedom from price rises for many years will make this a sound decision; no more complicated bills and compulsory TV licence either.  Anyone building a new house or renovating should give off-grid serious consideration from the start. This is mainly suitable for ex-pats not paying tax in Italy; tax payers should still check out the grid connected route now that there are substantial price falls in panel prices.

 

England

Back in cloudy England our panels will be less punchy and electricity only costs about 14p per kW.hr. The chances are that after 5 years you would still be out of pocket by about half the investment and needing another 4 or 5 years to break even, and there will have been a £1,000 battery hit too. Even so, that leaves another 10 years or so of free electricity and with prices likely to have doubled by then this isn’t at all a wrong move. So yes, grid-parity is here but not the hugely compelling no-brainer that will start a mass exodus from the grid.

 

Grid connected system

Almost shocking price falls make a grid connected system worth a look. The kit does away with batteries and charge controllers; just panels (say 14 at £105) and an inverter (4.2Kw Growatt Inverter 4200 MTL-S Dual MPPT £515). So £1,985 plus fitting gives a chunky (but day time only) power source which, according to The Energy Saving Trust, will give annual benefits of £370. Sainsburys want £70 a month for a £2,500 loan which is too expensive (24% apr) so you’d need to look around or use your own money for a tax free return of 14% for 20 years. Your capital is sunk but even so this is a good return and ahead of grid parity.

If on-grid takes your fancy then you need to call your local MCS approved suppliers to see if you can get registered before 31st March 2019 when the FITs scheme ends.

Now that the lines have crossed, PV deals of all sorts can only become better as time rolls on – watch this space. Note that off-grid systems are surprisingly simple and fairly DIYable whereas on grid systems need a certified expert to install.

PV – overclocking

You can improve the performance of computer chips by overclocking them and, although there is no particular similarity, the same name is used for overpowered PV systems.

Usually charge controllers and/or inverters match the input power of the panels, but as most of the time the panels do not make their full power it pays to have a bigger array – maybe 30% bigger, say a 6kW system with an 8kW array. On those rare sunny full-power moments the electronics will limit the excess input power by what is known as clipping. Most of the time though the system runs in the more efficient part of the power curve turning bad production days into something useful.

A further tweak that really suits overclocking is to tilt up the panels to a winter biased angle. Panels look at the sky and overall light levels so 45 degrees is a good winter angle. This tilt fattens the shoulder months and tempers the power in the summer where the peaks would be clipped anyway.

So the overclock and tilt concept gives much better utility at the expense of overall production but this doesn’t matter where there is no FITs return to consider.

PV overclock and tilt

Dotted red line – where clipping tends to limit production; not a straight line in practice.

Blue line. kW.hrs per month produced by a 6kW array with a 20 degree tilt – no clipping.

Grey dotted line. 8kW array still at 20 degrees – not a great winter gain, high summer clipping.

Red line. 8kW array at 45 degrees – big winter gain, minimal summer clipping.

Note the significantly wider shoulder months and winter production almost doubled.

N.B. Tracking panels grab morning and evening rays so they absolutely love overclocking.

The sun tracking garage loves overclocking.

 

 

 

Solar thermal panels – a bad week?

Our overclocked array almost certainly knocks out the viability of solar thermal panels ( the wet ones with fluid pumped round.) A few more PV panels now have a similar cost to a full solar thermal set up. In winter, when we need to finesse all our kit, the wet panels are often connected to a hot tank so they don’t even run at all. Meanwhile PV panels will still be involved in the plot by running a heat pump (output 3 x input) or an immersion heater. PV plus heat pump is the future. In the summer the PV panels will be over producing so there is no need for another system.

The only way to justify wet panels could be to run my ‘solar stripper circuit’ as on the eco- heating system here. I’ve been running this circuit for years and it is wonderful to see the solar panels running almost every day of the year even when paired with the log burner.

Wood burning stoves – a bad week?

The Government Clean Air Strategy had some bad things to say about stoves and they were right. A stove running cool and with wet wood will emit a lot of smoke with particulates to match a diesel truck. However – properly designed stoves, running hot and burning dry wood, are so much better; the stoves I supply can even be used in London.

Trees are generally good for the environment but when they die or are used for some purpose there will inevitably be wood to be disposed of. If left to rot there will be no particulate emissions but there will be no return for the grower and less incentive to plant more. Any clampdown on stoves could lead to less tree planting and wood going onto bonfires – both disasters. As open fires, both outside and in the home, generate huge amounts of particulates it looks as though stoves are actually the answer, with all that lovely heat and light helping to keep the air clean.

I know that the open hearth is still a popular feature but this particulates argument adds another reason to upgrade to a stove. The other reasons being that open fires burn about 5 times as much wood for the same heat and when it gets really cold the replacement air can make an open fire go negatively efficient. Air conditioning in winter!

That’s all for now. If you need advice, a stove or a heat bank in UK, France or Italy please contact me.

Heating News – December 2018 – Zombie Apocalypse Edition

Heating News December 2018

Zombie Apocalypse edition.

We’ve covered the heating of old farmhouses so much already that if you are not in a house that is warm, cosy and cheap to run then you haven’t been paying attention. What about the Zombie Apocalypse though? If there is a power cut, all heat pumps, gas and oil boilers and most PV systems don’t work so a wood burner will be handy when the grid gets hacked, whether by Zombies, Russians or just bad weather. Connected to a heat bank that wood burner will provide heat, cooking, functioning radiators so not just a nice thing to have but maybe even a life saver.

But enough about that. Not everyone has a leaky old house with a siphon attached to their wallet. The other end of the spectrum – a Passivhaus – is pretty astonishing with heat losses so low that just by turning on the lights, TV and computer would pretty much cover the heating needs.

 

insulation matters

This diagram shows how energy demand falls as insulation values rise. The Passivhaus demands are so low that heating is hardly needed. It’s not just running costs that are trivialised. The actual build costs are reduced because there is no need for under-floor heating and no powerful heat sources to drive it. Usually a small heat pump using no more power than an electric kettle will be more than adequate.  This is offset by the cost of extra insulation but the savings are there forever and the Government RHI will pay for the heat pump too.

So what is a Passivhaus?

It’s all about insulation and airtightness. Insulation of walls floor and roof have to be slightly better than current UK regs, but not by that much, and the building must be a bit more airtight than usual but again not by that much. Heat loss is measured by U values (which we’ll examine below) and airtightness is measured in air changes per hour. Basically a fan blows up the pressure to 50Pa for a maximum of 0.6 air changes per hour and then the same again but with a negative pressure. A Pascal is the pressure of one Newton/sq metre so a bit like a minced apple spread across your desk.  50Pa is very low so with careful building and lots of tape the standard is achievable. Sealed doors and windows will close with more of a ‘schmwuk’ noise than a clunk and the house will probably feature triple glazed windows and mechanical ventilation with heat recovery MVHR. Passivhaus gradings relate to how much renewable energy they give back so for the top tier ‘Super’ the roof will be heavily covered by solar panels to make 120kW/m2/annum (footprint). The overall target U value for a Passivhaus is 0.15W/m2K so lets see how that compares with traditional practices.

U-Values

This value relates to the ability to flow heat energy across a surface so it is measured in Watts per square metre and takes into account the temperature difference across the surface, so W/m2K. So a Passivhaus with an external shell of 800m2 and U=0.15 would need 1.2kW when the outside temperature is 10 degrees colder. This ties closely to the Passivhaus limit of 15kW.hr/m2/annum (on the footprint) for total energy consumption.

Traditional practice U values  W/m2.K

Brick wall                          2

Cavity wall                        1.5      Note: this is 10 times worse than the example above

Insulated cavity wall      0.18

Concrete                             1.5

Single glazed                    4.8 – 5.8

Double glazed                  1.2 – 3.7

Triple glazed                     < 1

Wooden door                    3

Note that some popular modern building methods are not really up to scratch and need extra insulation to get towards Passivhaus. Eg Durisol insulated concrete forms 0.15    Structurally insulated panels 0.14. Adding extra layers of insulation is needed and to get the final U value you add the reciprocals of the U values of the layers then take the reciprocal of that for the final figure.

Current SAP rules

Wall      0.18

Floor   0.13

Roof    0.13

Glass   1.4

No doubt you have noted that glass is a five lane highway for heat loss especially on the North side of the house. South facing glass is different because it behaves just like a solar panel and gives back much more than it loses. For example the daily solar insolation average in Kw.hrs per square metre (Brighton) is: Nov 1.7, Dec 1.14, Jan 1.43, Feb 2.17. The obvious conclusion is that lots of south facing glass is often good enough to heat the house especially if accompanied with high thermal mass floors/walls and covered at night with shutters and curtains.

Now we have a house that barely needs heating and sells power to the grid but there will be days when some heat is required. The bills here are going to be so low that the choice matters less, but for a small house I’d go for a low powered heat pump because:

Heat pump power

The RHI payments are good, it’s ecologically sound, it runs on similar power to an electric kettle and the PV panels will run it free on most days.  Air conditioning can be incorporated when partnered with fan-coil units. N.B. There is no RHI for aircon enabled heat pumps so a separate chiller unit would be required.

What about a wood burner? – well of course, we love them and there is the Zombie Apocalypse looming.

DIY fan-coil unit

DIY fan-coil unit

No underfloor heating, no radiators, it has to be fan-coil units. There is a full description of the Original Twist version here.

It’s a cheap and easy DIY project.

 

1st year with Google Home and Chromecast

Verdict: So good we have 3. Main uses, TV control, intercom, encyclopedia, alarm.

Radio? They’re obsolete

Remember when a DAB radio with preset buttons was a Christmas present favourite? Well those days, in a flash, have gone. A Google Home will tune in practically any radio station; all you have to do is ask. Turn up the volume? “Hey Google, turn up the volume”  “Hey Google set an alarm” So it’s a radio but, of course, so much more with your Spotify playlists to hand, and via Chromecast, control of the TV, Netflix, YouTube … etc … but you know all that. It’s just fascinating how as an almost inconsequential aside this device has consigned an ubiquitous bit of kit to history. Will the next generations even know what a radio is.

That’s all for now. If you need advice, a stove or a heatbank in UK, France or Italy please contact me on the form below.

DIY fan-coil heater

DIY fan-coil heater

DIY fan-coil heater

And actually the best fan coil heater regardless of price.

If you are wondering how a heat pump might (or might not) work at all with your old radiators and pipes this might give you the answer, and it won’t cost too much

You might be surprised to know that if your house build is anywhere near Passivhaus standards then minimal heat demand makes underfloor heating a waste of time and money. Well, that’s a big saving so bring it on but what to do instead?

Underfloor heating did away with horrible radiators, and we don’t want them back, so that just leaves warm air blowers such as kickplate heaters – i.e. water powered puffer heaters..

On the walls without plaster theme here I proposed a kickplate heater, in the lower cupboard part, to give an occasional guff of hot air and for slightly under £200 you can do just that. However these neat little units aren’t perfect. They have to shift a lot of air through a small aperture so they are intrinsically noisy, draughty and the heat exchanger, or a filter, can clog with dust and pet hair fairly quickly. Larger versions are available but they aren’t so neat and they are much more expensive.

So here’s the Original Twist fan coil heater which is cheaper, quieter and more reliable. Double click this picture for a better look.  Can’t see the heater? Neat huh.

cupboards with fan-coil heater built in.

Lets assume that the low cupboard bit of your wall is made of typical 720mm x 300mm kitchen carcass units. A pair of them 600mm wide with a large slot cut out of the inner sides allows a 1000mm x 500mm x 70mm double radiator to fit inside (£48 Screwfix). Each of the top shelves is fitted just low enough to mount a 140mm fan from a computer (£10 – 20 Amazon etc) and these gently blow air past the radiator and out of the bottom. You can decide where the air inlet goes: probably top front but a wall panel channelling much warmer air from ceiling height is worth a thought. Note that this is much smaller and neater than the huge radiators you would be trading up to if you were trying to make a heat pump conversion work.

When paired with a suitable heat pump this unit also does air conditioning if that’s what you want hence the length of plastic guttering under the radiator to catch any condensation.

N.B. The Heat Pump Incentive does not support heat pumps with integrated aircon but you can still get it if you use a separate chiller unit – see the Originaltwist hybrid heat pump concept which does chilled water as a free extra. Before you get too enthused about that though, have a think about a separate mini-split aircon unit (a very cheap heat pump) which delivers hot or cold air with a much simpler installation. Cold air flows across the floor so spreads around the house surprisingly well. You don’t need multiple sources like you do for heating.

You might want to kill airborne pathogens. There is plenty of space in the box for a pair of UV lamps but if you do fit them then avoid or wrap PEX water pipes because UV will kill them too. Fitting UV tubes in the top sections with the fans underneath is the way to go.

Controls:  The fans are switched on automatically when either hot or chilled water arrives at the radiator. An ESCO solar controller does all that for £45.50 or about half that with a frost stat and a 2 pole thermostat. If you are omitting the aircon side then any solar controller will do the job simply enough. You’ll also need a variable resistor for speed control. The fans are 12v so you’ll need a power supply and, like the fans, these are cheap PC components. Remember that the LED strip lights in your integrated beam floor could be 12V and might like to share that power supply.

Cleaning:  Open the doors and Hoover it out – easy.

And that’s it really. A few simple components all easily obtained and making the perfect, reliable fan-coil unit. When turned down to essentially silent the fan pair will move about 100cfm and the heat output will be between 1 and 2kW depending on the water supply temperature. Turning up the fans will double this.

You might wonder why all this effort gives you anything better than the same radiator fitted as normal. The answer is that heat pumps don’t work efficiently at the 60c+ normally used with radiators. While under-floor heating is the best at very low temperatures a fan-coil unit works reasonably well at 40c. The only reason our unit has a radiator is that with all the fins in a double radiator you get a high surface area for not much money. The heat delivery couldn’t be more different. A radiator wafts hot air straight up to the ceiling where it tends to remain – with replacement  air moving across the floor as a cold draught. A fan-coil on the other hand, blows warm air across the floor where it mixes with cooler air to give a faster and more comfortable heating experience.

Some extra mods

If you want to direct warm air somewhere in particular, patio doors for example, then a row of slats on the exit slot can send the air to the side. To go further with directing air flow you can also fit a duct or two to the bottom of the unit. This might be useful if you were trying to warm the air near those patio doors. In a new build you could fit a drain channel beside the doors (those ones with the clip-on metal tops) and blow hot air into the ends of the channel. That same channel could also be used as a handy route for the heating pipework and as an added benefit it makes the channel into a radiator in its own right.

If you have an MVHR system in mind you could run your return duct into the top of this unit with the benefit of hiding the outlet and getting a free blow from the MVHR fan.

What about the bathroom?

Now we’re talking. The perfect place to  have hot  air blowing especially when you are drying yourself. For a start I’d turn the unit on its side so the air is blown from a vertical slot, then I’d go one step further and have a pair of them in a corner so you step into a sort of Dyson hot air blaster, like a giant hand dryer. Smaller bathrooms could have an opposing pair. Electricity in the bathroom!  No worries there, it’s all 12v.

insulation matters

Have a look at this chart on heating costs for various house types to appreciate why a Passivhaus with a small heat pump and some fan-coil units could be the way to go. You’ll see that the ASHP can meet the Passivhaus demand for almost no cost. Indeed if the ASHP is connected to PV panels then the running cost of the house will be close to zero. This chart is out of date now. I did a new one in October 2022 when all the new rates were fixed. here

The results are startlingly different so take a look and see if you agree with my comments.

I guess you might be in a state of shock now. Thousands saved on your heating strategy, the government might buy you a heat pump and air-conditioning can be a simple addition.

For more money saving shocks check out more building ideas on LIST OF POSTS.

If you’ve built this please let me know on the comments form below. We’d all love to see pictures.

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