Category Archives: Eco-house

Off-peak energy storage for cheaper heating

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High temperature heat pumps are a game changer. How about a sub £500 heating bill for the whole winter? Higher temperatures present a new opportunity to store cheap energy in a heat store (a large buffer tank).

Off-peak electricity costs a third of the day rate allowing heat pump energy multiplication to produce unbelievably low-cost heating (like 2.5p/kW.hr).  A heat store can time shift the night rates to the following day with that energy simply dispensed to underfloor heating and fan-coils by blending it back down to the required temperatures. With energy this cheap the inefficiencies of large buffer tanks and blending are hardly relevant.

Large tanks are better for high temperature heat pumps which don’t like short cycling and prefer a large volume of water to chew on so that’s another win.

For example: Over 5 hours a 12kW heat pump can place 60kW.hrs in 1,476 litres of water raised from 30c to 65c. As the model lower down shows, that costs just £300 over 200 days of winter. Similarly,, a 1,000 litre tank, plus a large hot water cylinder and a heated floor slab make a good combination to store this night time bounty ready for the next day.

Cheaper than a battery

A 1,000 litre tank can store 40kW hours and costs about £1,500. A battery that can make 40kW.hrs (via a heat pump) would cost twice as much and could wear out after 10 years. Water lasts forever so works well as a storage medium; it doesn’t even burst into flames. Having said that, batteries are still very useful and will become strategically important when you access the very large one in your car. The battery is the top performer in the chart below because the heat pump will run a better COP during the day.

N.B The 7.5p off-peak rate is for electric cars but economy 7 is a workable alternative.

A much bigger heat pump

In order to bank the entire heating load over just a few night hours the heat pump will have to be significantly bigger than normal. 12kW is a good place to start especially if only single-phase electricity is available. The Samsung EHS Gen7 R290 12kW is a good example.

Additional power

The calculated heat loss of the house must be matched by the heat pump power (to get the grant) and, on paper, a big heat pump will easily meet that requirement but the stored energy may not always meet the actual demands of the day. Cheap power is time limited rather than power limited.

If there is the occasional shortfall the heat pump is still there to give a powerful boost – at a lower set point to leave the water-battery ‘empty’ as it goes into the night – however there is a better way.

Part of a sensible strategy is to have another smaller heat pump (like a mini-split) that runs mainly free off solar panels. Obviously this helps to keep the electricity costs down but also gives the option of topping up when necessary at minimal cost. The blown air of a mini-split is immensly useful for laundry drying and the cooling feature gets the air-con requirement largely sorted too. Forget the daft headline costs of regular heat pumps – mini-splits can be bought for around£600 and you’d get one fully installed for under £2,000.

Domestic hot water

To store off peak energy the 300 litre domestic hot water cylinder has 3msq coils for heat pump use. It may require a trickle charge during the day and instead of repeatedly firing up the heat pump an EDDI solar diverter tops it up via a Willis remote immersion heater (better for stratification and servicing if you were wondering). The EDDI captures even tiny excesses throughout the day to produce a higher temperature and the lost exports are about equal to the cost of running the heat pump.

System benefits

Water is usually hot enough to make towel rails work properly.

A large domestic hot water cylinder needs fewer daytime top ups if any.

The big heat pump gives faster DHW recovery times (if needed).

Fan-coils take from the hotter level of the heat bank.

Fan-coils can tolerate high temperatures so a boost mode is possible. Eg. 5 mins of full power on startup to give fantastic response times.

Heating can be zoned without complications.

Off-peak electricity is mainly renewable so this system is as green as Kermit.

Daily characteristics

In the morning the tanks will be hot and ready. The bathrooms will be toasty with the towel rails on full pelt. The bedroom fan-coils instantly transform a cold room into a warm one and there’s loads of hot water for showers. Downstairs the floors are already warm.

The towel rails stay on for a while but all else takes a rest until the floor slab downstairs calls for a top up from the big tank. With a bit of sunlight the EDDI starts to reheat the hot water tank and the mini-split might be able to run free.

At this point the big heat pump has not run at all, at any time, during the day. However, by the evening the temperature is getting low in the big tank, the floors can continue to keep warm even with water down to 25c but the fan-coils may need a last-minute boost from the big heat pump. UFH in bathrooms is a good counter to the possible end of day shortfall. Note that this is all fine tuning to avoid costs; if more heat is required then the system can perform just like any other and in fact even better.

Controls

Every thing is much simplified with no interlinking of elements.

The heat pump is allowed windows of operation on a timer and tank thermostats.

The night time set point would be 67C and 45C for the day.

The UFH is timed and controlled by a thermostat with an ESBE mixer if weather compensation is required.

Fan-coils (OriginalTwist DIY units of course) are timed and thermostatically controlled locally.

Simplicity

There are many options to add sophistication to this system; weather compensation, ESBE electronic temperature reducers, DHW via plate heat exchager, blending down for fan-coils, fan-coils boost feature, air source GSHP boosting (as per the OriginalTwist hybrid concept), batteries.

All should be weighed by the PV test: would the money be better spent on more PV panels?

ZERO COST HEATING

As you increase the size of a solar array so the energy bills fall and the export tally rises. For some well insulated houses the income will pay the electricity bills – ZERO COST heating has just become easier.

From the chart below you can work out how many kW.hrs your current system requires over the winter. Just compare each £1,000 bar with your own bills. 25 -30,000 kW.hrs would be normal. Ultra insulated homes nearer to 15,000 and only about a third of the way up a £1,000 bar. Note how the off-peak system is easily twice as good as anything else though don’t compare with direct electric heating unless you want to cry.

Just how cheap for 200 days of winter?

The Original Twist model of this entire system looks something like this:

A 12kW ASHP running for 300 minutes a night charges a 1,000 litre tank, a 300 litre hot water cylinder and the floor slab.

Over 200 days of winter this makes  12,000kW.hrs for £300. No, that’s not a mistake, £300 for 200 days!

The 3kW mini-split adds 1,000 kW.hrs for £125 (half from PV).

Total cost for 13,000 kW.hrs is £425 and less with large PV.

The same energy would cost £500 more with conventional daytime heating.

Could these trivial heating bills be covered by solar exports – maybe.

Ground source heat pump?

You’ll see on the chart below how night time use of an ASHP (blue line) is particularly disadvantageous compared to a GSHP (black line) which doesn’t really see any significant changes in source temperatures. From that point of view it might seem that this system will be optimised by using a GSHP for the night runs and an ASHP for the day time back up.

Furthermore the GSHP will not suffer the defrosting cycles which will eat up into the precious off-peak time.

Off-peak running of an ASHP roughly halves the heating bill but strangely the GSHP doesn’t gain much because the night rates are so low. Something like £100 a year does not seem worth chasing with a GSHP.

You won’t find an R290 high temperature GSHP either: that’s because they are fitted indoors and spilled R290 is toxic. The 10kW IVT GSHP might scrape in as a contender though.

Conclusion

This idea can be scaled and tweaked to suit individual requirements but the underlying message is convincing.

Off-peak electricity can be time shifted with large amounts of water to dramatically cut heating costs.

A concrete slab also stores heat usefully so a boost at the last hours of off-peak could be part of the mix.

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.

Heating system for heat pump – 2020/24 revision

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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 the lower set point, heat is sent directly to the cooler heating side without disrupting the stratification in the hotter 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 and for absolute perfection I’d have an external one – e.g. the Willis (no short cycling and easier to service and delivers heat to the top of the tank).

The cool tank has a large coil to preheat the DHW going to the hot tank heat exchanger and now there is a large choice of suitable tanks thanks to the heat pump drive. 3sqm of coil surface is common.

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 another 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.

There is a commonly recurring problem with heat pumps and that is that existing pipework is too small to deliver much more than 6-10kW. The solution, of course, is to stick with the low powered heat pump and add a mini-split air to air heat pump.They are cheap, independent of any existing systems and they do aircon. This immediately ducks all the attendant problems with transmission and low power and makes the whole set up even simpler.

With a mini-split on board you might go really simple and have just one heat bank, a wet connected stove, a gas boiler (get one while you can) and no other heat pumps. All very simple and enough money saved to buy some PV panels.

….. and don’t forget the Original Twist fan-coil units – too good to miss.

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 on dark and cold days or, as some might call it, winter

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.

There’s a pipe coming out of the GSHP unit and then going to the slinkys and we need to insert a small buffer tank here. So far there is no change to the performance at all until we go on to warm that tank with air. Just connect a 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. Any time the air is warmer than the tank -click – the pump and the fans kick in.

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.

We can go one stage further and by-pass the slinkys altogether if the air side is powerful enough. 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 £7,500 for an ASHP and £????? 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 in the tank can send the cold to the main heating system and onwards to the fan coil units.  Aircon sorted for almost no cost! Having said that; a separate mini-split aircon unit is a much better idea and has other benefits when used alongside a heat pump.

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.

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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DIY fan-coil heater

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DIY fan-coil heater

DIY fan-coil heater

And maybe 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 could even make underfloor heating a waste of time and money and there are very good reasons not to have it in bedrooms. 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 and bigger fan-coil units – i.e. hot 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 in this sketch is made of typical 720mm x 300mm kitchen carcass units, (just like your top cupboards). A pair of them (each 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. However, 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 hot water arrives at the radiator. A bi-metallic thermostat switch will do the job simply enough – RS Components do one for about £8. It clicks on at 40C and off again at 25C. There are no sensors; the switch can be glued directly onto the radiator near the water inlet. 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.

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.  Replacement  air then moves 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 directed 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.

MVHR reheat  The MVHR system is essential in a modern house but as it is not 100% efficient it does cool the house slightly so using one of these fan-coil units as a re-heater is a neat and inexpensive route to perfection. 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 but the message is the same.

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 unit 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

 

Modern floating staircase

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DIY floating stairs

How hard would it be to make a modern staircase to embellish your new build house? Not too hard is the answer, as long as you design it to be DIYable from the outset.

This modern staircase is based on two 100×50 HRS hollow steel box beams with chunky wooden treads supported on 40x40x6 bright mild steel angle iron support bars welded onto the beams. If you are handy with a router and a welder (MIG is easy) then the construction should be quite straightforward.

The angle iron bars are completely hidden inside the treads which appear to float without any means of support. Double click the image for a closer look.

The slot shown under the front of each tread is for LED strip lights which can be bought in aluminium channels with diffuser covers. Leave a little space around and under them for cooling and rout out a channel under the angle iron for the wires. You also need a hole through the angle iron and the box section for the wires to pass into the box section, preferably with a rubber grommet. All the wires go down to the bottom step which will house the control elements for making the lights do all the tricks you can imagine. The stairs lit with any colour you chose will be absolutely stunning.

A bought in staircase like this would cost at least £5,000 – £10,000 so you can afford to sub out some of the work to make it easier and buy any tools you need. The routing work is very repetitious and it would be worth getting a local CNC router on the case; there is only about an hour of machining time and accuracy will be perfect. Get the angle iron brackets cut to length too. There will be many chamfered holes to make so I’d say a pillar drill will be essential.

The Design

stairs geometry

Tradition has it that a comfort stair is 7” x 11” for rise and going. Rounding up slightly that’s 180 x 280mm. B.S. regulations give ranges for rise of150 -220mm and 220-300mm for going G. The ratio of rise to going gives an important angle which here would be around 33 degrees and must not exceed 42 degrees. You’ll need this angle to saw off the ends of the beams.

The distance H between your two floor levels will set the rise. Find which whole number divides into H to give a rise R near to 180mm or what you prefer. That whole number is one more than the number of treads but note that the bottom tread might be a platform like the one on the sketch above.

Tread thickness T.  B.S. regs state that a 100mm ball must not pass between stairs or guards so if we say that the open gap between the treads will be 98mm then T = R – 98 or more.

The Going overlap. B.S. regs state that the overlap on open stairs must exceed 16mm but too much spoils the design, as you will see when you draw yours. So tread width W = G + 20 will do for a start.

So the treads will be something like 300 x 80 in section. As for length just bear in mind that stairs over a metre wide must have hand rails on both sides. I think 85cm looks about right.

Length of box beams L. To make life easy you could set the top of the box beam level with the top of the top tread, so; The base of our triangle is (no of treads -1) x G / R and then just use Pythagoras to get the longest length of box…. or, frankly, just draw it and see what you get. The drawing will reveal what angle to cut on the ends of the box beams too.

Make a note of all your numbers then make a drawing of the side elevation to scale. Sketchup is perfect for this and is free and easy to use. Note the intersection of the top of the angle iron, the beam and the back of the tread. N.B. Sketchup can repeat copies easily so draw and colour just one tread then copy it upwards by the rise and then across by multiples of the going.

Safe assembly with no cock ups.

After drawing the beams etc, cut the angles on the beam ends and with the beams lying on a flat surface weld on a few cross stabilisers to secure the shape; they must remain dead parallel. The beams have cross plates welded across the ends but bolt these on to the wall/floor first then weld on the beams assembly in situ. So far no risk. Now take a fully assembled tread unit and fit the only tricky tread, the top one. Make sure that is going to work with the top floor level then clamp and tack it on. All the rest are easy and risk free. Start from the top to prevent weld spatter from spoiling lower treads and grind off the stabilisers as you go. Don’t do the final welds until you are sure it is all perfect. N.B. it’s the tread positions that matter; any minor inaccuracies on the angle iron supports are hidden anyway.

If you make these stairs I’d be very glad to hear about it and to put  your photo with this article.

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:-

Heating for your eco-house

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

You really should get the heating right and there are many wrong turns where multiple energy sources are integrated. More on this topic in LIST OF POSTS

Integrated Concrete Beam System

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Integrated Concrete Beams

Building with Durisol, Quadlock or any other ICF blocks? Here’s the easy way to do a poured concrete floor.

Concrete first floors are good; low noise transmission, high thermal mass and suitable for under-floor heating. The trouble is the shuttering required is elaborate and expensive both in materials and time and once the floor is poured there is usually more work involved in boarding, plastering and painting. Concrete block and beam systems look easier but you do need to be very organised and get delivery of exactly the right beams and after paying for heavy lifting gear they won’t look like a cheap fix. Again there will be final finishing to do. Plastering and painting ceilings – no thanks.

The Original Twist Integrated Concrete Beam system is so suitable for the self builder that it is hard to consider anything else. It couldn’t be simpler. You make up some hollow beams out of easily sourced planks, put them up in a row, fill the gaps with wooden floorboards and pour. That’s it.

Concrete floor system

Step 1/.

Make up the wooden beams as shown in this cross section. The blue and yellow bits are your choice of regular timber from your local supplier.  The slots sawn out of the yellow sections are for wiring channels and it makes sense to insert the wires while the beam is being assembled. The threaded studding stops the beam spreading when the concrete pours in and is part of the construction with the outside acorn nuts making a decorative feature. Use a spindle moulder or router to round off the edges and then apply your choice of finish after distressing with chain, hammer, belt sander etc. You will see that the yellow sections stick up by the thickness of your floor planks and make a perfectly curved transition between the concrete floor and the integral ‘I’ beams. The rebar at the bottom of the ‘I’ section needs to be held in position prior to the pour and this can be done easily and cheaply with pairs of cup hooks screwed into the bottom plank. Use cable ties across each pair to hold the rebars in. Finally, paint the inside of the beam to isolate it from the wet concrete. The beams are then ready to be placed in position, typically on a one metre pitch (Durisol blocks are half a metre wide) and each propped with one or two Acrow props. If you are using ICFs like Durisol for your walls you should cut out large slots on the inside face to take the beam ends. You might want to pour the walls up to the level of the beam bases now.

Step 2/.

The floor planks can be cut and finished at ground level before fitting between adjacent beams. Now is the time to fit any pockets for spot lamps and take the wiring back towards the slots pre-cut in the main beams. The floor planks need to be strong enough to resist the weight of the concrete without sagging; they don’t need to be jointed together as a layer of building paper over the top will stop any leaks. Unlike concrete blocks they are light and easy to pass up to your helper.

Step 3/.

With steel mesh over the beams and planks the floor is ready to pour.  The outside of the Durisol blocks sets the top level of the floor so you don’t even need any shuttering. Once the pour is done and set, the walls and floor are all integrated with the homogeneous ‘I’ sections in the beams giving enormous strength and stiffness. The ‘I’ section parts of the floor could be up to 360mm deep which makes them into a row of significant beams in their own right. At this point the lower part of the house is waterproof which makes for a good working environment from which to finish off the rest.

Step 4/.

Nothing much to do now. Just take down the props then go down to the pub to celebrate all the money and time you’ve saved. There is no ceiling finishing to do, no shuttering to take down, even the lights are fitted and wired. And all this was done with simple hand tools and without waiting for special parts to be delivered. And just look; lovely lovely beams adding character and value to your home.

Notes:

A small spacer between the top of the beam and the floor joists will create a gap to house some LED strip lights. As you have a lovely wooden ceiling you might as well show it off.

N.B. Wood shrinks. A tiny air gap could eventually appear between the concrete floor and the wood floor. A very thin rubber membrane between the floors (instead of the building paper) will prevent any ‘thwack’ as the upper floor is walked on.

Ground floor block and beam – alternative system

Block and beam systems are commonly used for ground floor construction but again they can’t compete with our integrated beam system. Block and beam materials all have to brought to site and then assembled – lots of work there. All those blocks are more gap fillers than strength givers and they are followed by a poured screed anyway. With the integrated beam system you just string out the wooden beams, fill the gaps with plywood and then pour – not only much quicker but stronger too. Use adjustable legs from kitchen units as props, to prevent sagging, and leave them there forever.

With both floors quickly and cheaply constructed and the walls easily made with ICFs it is easy to see that a fully waterproof house up to the first floor could be made in a matter of just a few days. That saves time and money and less exposure to problems with bad weather.

structural fireplace and stove.

While the rest goes up the internal finishing can start on the first level. Some comments on this here…. and an internal wall cum fireplace design here. … and a floating staircase here.

While this system is great for under floor heating, I’m really not in favour of it for bedrooms as it is a big waste of money for an unwanted result. More on that in the eco-heating link below.

N.B. As usual do your own evaluation for suitability.

Heating for your eco-house      For essential reading 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 house building topics in LIST OF POSTS