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.

Hybrid Heat Pump

Hybrid Heat pump by Original Twist

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 (ASHP), a feature in keeping with the free power from PV panels.

 

 

showing the COP difference between ASHP and GSHP

Day COP vs. Night COP

I tend to favour the cheaper and simpler ASHP and this chart shows why. 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. After that the daytime COP on the air source starts to improve while the ground source continues to deteriorate.  This is all reversed at night when the ground source is miles better than the air source blue line.

Even though the GSHP easily beats the night time ASHP (blue line) 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 (5p/kW.hr at night) make a GSHP, with more night time running, quite compelling. It might not be quite so efficient but the running cost is only 25% that of daytime rates. The biggest attraction though is the Renewable Heat Incentive which is heavily biased towards GSHP at 20.89p/kW.hr versus half that for ASHP. In my view the Government have not thought it through properly; the rates compensate for the cost difference  between the systems and not for the performance gap if indeed there even is one.

If only there was a system that could cherry pick the best COP line on the chart for any particular moment but still keep the high RHI payment. 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. The average COP over the season would be around 4 which improves on the ground source while still keeping the best incentive.

Such a system is easy really and not particularly expensive either.

 Original Twist Hybrid heat pump – it’s a GASHP.

overclock and tilt PV panels

PV overclock and tilt

This system is particularly suited to the off-grid brigade who need every trick to make a limited energy supply (like the 6kW overclock and tilt)  go further.

 

 

This is what makes up the system:-

GSHP unit

We start with a GSHP unit. I saw a 3kW one on EBAY for £1,500; maybe not MCS approved but that looks like a fair price for a unit that is actually simpler than a complete ASHP.  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 a couple of car radiators and a fan or two to make the equivalent of an ASHP for about £200. A simple solar controller brings in the AS module whenever it can contribute.

The air module can be a fairly simple DIY job:

Rads in back of a kitchen cupboard, fans in the door?    or

A trestle with rads either side and a fan in the base.    or

A stand with rads and 12v car fans – all waterproof.

Hybrid heat pump

Buffer tanks

Two buffer tanks are used to handle the cold water coming out of the GSHP and the warmed water going in. The tanks allow 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 heating demand is on or not. The cold tank will nearly always be available to charge and sometimes the hot tank too.  Like the solar stripper circuit on the heating system the solar controller switches tanks easily and simply. When the colder tank is warmed up the flow back into the slinkies 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.

 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 slinkies 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.

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 design is avoided.

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 would be just as good and cost under £300.

Air conditioning

The RHI rules forbid a combined chiller unit in the GSHP unit. No worries there mate. 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, full RHI payments, aircon, ground loop recharge, smaller ground loops and much kinder to an off-grid PV system.  The smaller ground loop might just swing this for owners of regular sized gardens.

Thought for the day

The RHI pays for heat made but not the electricity used to make it. So on a COP of 4 they pay for an effective COP of 3.  So if we ran a 3kW GSHP for 4 hours at night on 5p/kW.hr (electric car rate) it would cost 60p. But we would be paid for 36kW.hrs produced at 20.89p      £7.52  NICE!

So, your PV panels run the heat pump for free during the day and you get paid for night time use – makes you think eh?

(Actually the RHI pays you based on your EPC total heat demand with the rate at 20.89p/kW.hr, and for 7 years too)

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 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.

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

automatic connection for charging

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. 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

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.

 

 

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 and the actuator starts off 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.

 

Rotating, 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; 6 powered wheel units (electric or hydraulic) enable you to go for a trundle, down to the pond to watch the sunset for example. Steering is done from the glazed conservatory at the front or from outside.

With the wheels steered inwards the whole house can rotate on its axis to track the sun, making full use of the 6kW photovoltaic array. So yes, it’s all off grid and only needs to dock occasionally to empty some tanks and to refill others.

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.

rotating house

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. Based on the rules and with proper panel dimensions this is a preliminary sketch to see what it might look like. The wheels could be a bit chunkier.

The space invaders look is intentional.

 

 

 

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 unit

Fan-coil unit

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 alternative which is cheaper, quieter and more reliable.

cupboards with fan-coil unit

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 (£48.14 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 channeling much warmer air from ceiling height is worth a thought.

This unit also does air conditioning when paired with a suitable heat pump hence the length of plastic guttering under the radiator to catch any condensation. N.B. The Renewable Heat Incentive does not support heat pumps with integrated aircon but you can still get it if you use a separate chiller unit.

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. 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.

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.

You might wonder why all this effort gives you anything better than the 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 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 in the room and gives a faster and more comfortable heating experience.

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 if not better.

 

 

 

I guess you might be in a state of shock now. Thousands saved on your heating strategy, the government is going to 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.