Category Archives: Eco-house

Radiators and heat pumps

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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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Heating system for heat pump – 2020 revision

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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

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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

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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.

 

Amazing AirBnb driveable house

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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

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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

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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

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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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Cool fireplace design

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On the theme of substituting alternative wall finishes for plaster here is a large brick fireplace that looks absolutely stunning with a wood burning stove and adds a bit of ‘wow’ to any room. Shown here, part finished, the brick construction is a structural part of the house with the essential offset from the main wall allowing the exposed brick to be part of the room behind. You were going to build a wall anyway so here a little bit of thought yields an expensive looking fireplace doubling up with a characterful wall on the other side.

Perfect fireplace for a wood burner.

A few dimensional suggestions: The front buttresses are 225mm or one brick wide and thus the wood sections are 225mm square. The width between buttresses of 1.6m gives room for logs to be stacked by the stove and the 1.5m height between the floor and the main cross beam works well.

fun with the band saw

The Zampi (Italian: paws) profiles go like this:

Draw a centre line, mark the radius from the corner, draw a 30 degree angle from the corner, the big curve follows from the centre line intersection.

Double click for a closer look.

 

 

You might be going to use a flexible flue and this will need supporting above the stove. A steel ladder frame that can be slid forward and back a bit will make lining up the stack and the stove really easy. Between this and the stove fit a removable flue section to make cleaning easy.

A big stove like the 14kW Clearview shown here is best connected to water or it will make the room far too hot. To get a simple gravity feed put your tank on the other side of the wall and inside an airing cupboard. That’s another lot of plastering avoided and the core of your heating system done. BTW – I’m happy to advise on tanks and stoves and to supply them too. There’s a contact form below.

P.S. Here is a 2m wide version drawn with the non plastered wall theme – i.e.with low cupboards that can incorporate the DIY fan-coil heater.

Inglenook fireplace

Like what you’ve read? Find more essential reading on my e-book

‘Dream House – Down To The Details’ 101 things you should have thought of.

Heating for your eco-house

For more straight thinking, this time on heating, have a look at the ultimate Eco heating system which integrates heat pumps stoves and solar.

You really should get this right and there are many wrong turns where multiple energy sources are integrated.

More on this topic in LIST OF POSTS

Alternative to plaster wall finishing

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The clean, white, boxy rooms of modern architecture are all very crisp and neat but the reality for the occupants can be that they make for clinical, boring and echoic spaces without much sense of warmth and homeliness. All too often money is spent on plastering which is then covered up. Think long and hard before plastering a kitchen wall before cupboards and splashbacks make that work redundant.

Similarly, there is no need to cover up plasterwork with a fitted bookshelf or cupboards especially double sided ones serving a room on the other side. Hey, you might not even build a wall here let alone plaster both sides, just leave a large opening.

The Original Twist integrated concrete beam system can make a beautifully lit ceiling with wooden beams and boards …. but what about the walls? You might be wondering how to finish the stack of Durisol blocks you built with. The usual plastering solution needs a certain amount of organisation; the first fix plumbing and wiring has to be done and then the plasterer booked for some slot later. From start to finish it could be at least a couple of weeks before the plaster has dried and been painted. Even then there are many things a plain plastered wall does not deliver, so let’s have a look at the Original Twist concept wall and see what extra benefits can be achieved. Here are some ideas incorporated into one picture – it doesn’t have to be this busy.

This or plaster?

Basically there are three or four transverse wooden beams fixed to the wall and then panels fit somewhat loosely and quickly onto them. Extra insulation can be particularly easily added at this stage.

The top beam section

This top beam has a rebate sawn at the back to allow the top panel to be held in place then dab bonded to the wall or a top batten. Pictured is a strip of plywood with vertical marks scratched to resemble boards; quick and inexpensive. Strip LEDs are then laid on top of and under the beam and hidden behind the pelmet board – an inverted strip of skirting board would be good for this. Note how lovely the panels will look when the lights go on.

The next beam down has a similar rebate and here the larger panels are pushed up first to hook under the top beam before dropping into place on the beam below. Our top picture shows an example of black ash faced panels with OSB panels fitted on top. The latter can be covered in anything from wallpaper to fabrics and give unlimited scope for decoration; they could even match a TV screen. If engineered floor boards are being used for this section remember that many of them come in 1.2m lengths so designing for that might save a bit of time and not leave any waste.

The lowest section takes on a colonial look with tongue and groove boards under a shelf. The point of this is that wires and pipes can be hidden as can tubes for integrated dust extraction. Fan coil units for heating and air-conditioning can be fitted into this space with the inlet and outlet vents facing down and hidden. If possible the height of this section should be like kitchen cupboards so that doors and hinges can be incorporated and some mini cupboards too. The underside of the lowest beam has a routed slot for another LED strip light which will highlight the lower panel which acts like a deep skirting board.

So there we have it; loads of character, good sound absorption, sensational lighting, lots of utility and all quite easily done by any DIYer.

Internal walls in blockwork can be visually tied in by using the same beams but leaving the blockwork as the finish. Blocks can be painted in different shades before they are laid to make an interesting textured look. Any other wall incorporating a fireplace can be made in exposed brickwork to give a structural element with exposed brickwork on the reverse side. By the time all the remaining areas are covered by glass doors and a bit of wood panelling there may be very little plastering to be done at all.

Like what you’ve read? Find more essential reading on my e-book

‘Dream House – Down To The Details’ 101 things you should have thought of.      here:-

https://originaltwist.com/2017/02/16/1370/

Heating for your eco-house

For another example of sensible thinking, this time on heating systems, have a look here.

You really should get this right and there are many wrong turns where multiple energy sources are integrated.

More on this topic in LIST OF POSTS