Heating in a well insulated house

chichikleine

Hi Robwiz,

Thanks very much for explaining the system to me. The problem is that I would want to heat every individual room separately, which would make it quite costly. And also, I have looked at pictures of them, which, as JohnandAbby says, are quite unsightly and may be too big in a small room....
Still, it is definitely an option we will have a closer look at.

chichikleine

Hi JohnandAbby,
The quote we have from the mvhr-supplier includes an option for additional heating of the air. We weren't sure if that would be necessary, but do you think this may be an easy way to ensure comfortable temperatures in the winter?

Smiley_Dan

An immerSUN (or equivalent) won't meet your total annual DHW requirement. As an anecdotal example, our 4kWp system covers it during summer and the brighter parts of spring with occasional top ups from the immersion (not had an autumn yet with the device). During winter it helps, but it's only on those cold, really sunny winter days that it covers use.

And even then it's because we shift demand - having later showers etc. If you *need* showers at 7am each morning it's only going to help with later usage.

A lot also depends on your current immersion setup. The above is with an immersion 1/3 down the tank. That means we lose heat through conduction slowly through the night. We have lagged all hot pipes to reduce convection out the top and you should too. Ideally you'd have two immersion coils: one at the top for winter and immediate use and one at the bottom to consume the rest and get the whole tank hot. I think if the whole tank was hot, 7am showers would be realistic.

If you have the chance to spec that you could be in a good position.

One issue you have though is that space for 10 panels isn't enough with current technology to reach 4kWp. With the most efficient panels you'd need space for 12. The standard, cheaper ones you'd need space for 16.

So you could ground mount if you have enough land. Another alternative is solar thermal which is arguably better for DHW (the panels run at a higher efficiency) but *only* work for DHW (or CH if you have a fancy setup). They don't help with electricity.

Johnandabby

chichikleine wrote: »

Hi JohnandAbby,
The quote we have from the mvhr-supplier includes an option for additional heating of the air. We weren't sure if that would be necessary, but do you think this may be an easy way to ensure comfortable temperatures in the winter?

It is one way of providing heating without additional heating installations BUT does normally require an increased MVHR size to achieve the higher ventilation rates required to deliver the required heating. There is a maximum supply air temperature of around 50 degrees Celsius to prevent the smell of burning dust being pumped around the house....


One major issue though is that there is then no control of the temperature in each room - the supply air temperature is set according to a central room thermostat, so some rooms can get too hot and some rooms can get too cold.


And if this extra heating requirement is quite large, then a direct electric heating coil in the MVHR will be an expensive (and poorly controlled) way of doing this.


Personally, I would look into an air source heat pump system feeding underfloor heating or oversized radiators throughout, with individual room temperature controls. This heat pump could then be used to heat the hot water cylinder as well, with the PV Panels providing a top up through the electric immersion heater in the cylinder. If you had a big budget, then I would probably look at a hybrid heat pump and LPG boiler system which selects the most efficient heat source to use - if you need lots of hot water the LPG boiler would provide this quickly, but not cheaply.


I really think you need to speak to someone about how all of the systems work together, otherwise you will spend a lot of money on something that won't work...

Robwiz

chichikleine wrote: »

Hi Robwiz,

Thanks very much for explaining the system to me. The problem is that I would want to heat every individual room separately, which would make it quite costly. And also, I have looked at pictures of them, which, as JohnandAbby says, are quite unsightly and may be too big in a small room....
Still, it is definitely an option we will have a closer look at.

Why do you want to heat every individual room separately? Are you really sure that will be necessary in a house as well-insulated as yours?

Robwiz

Johnandabby wrote: »

Personally, I would look into an air source heat pump system feeding underfloor heating or oversized radiators throughout, with individual room temperature controls. This heat pump could then be used to heat the hot water cylinder as well, with the PV Panels providing a top up through the electric immersion heater in the cylinder. If you had a big budget, then I would probably look at a hybrid heat pump and LPG boiler system which selects the most efficient heat source to use - if you need lots of hot water the LPG boiler would provide this quickly, but not cheaply.

I really think you need to speak to someone about how all of the systems work together, otherwise you will spend a lot of money on something that won't work...

In my opinion, an air source heat pump used for space heating and domestic hot water is the worst option as it's a real (and high capital outlay) compromise asking ASHP technology to heat water to 55º C. Cardew may be along any time soon to quote the Energy Saving Trust's report which showed that real world installations (even when optimised by the manufactuers) delivered COPs (coefficient of performance) way short of published specifications. And a COP of 3 is reckoned to be pretty good for air to water heat pumps whereas the best air to air heat pump achieves around 5.

The UK is one of the few countries where a combined space/water heating solution is popular – almost everywhere else in the world they keep the two functions separate and optimise both. An electric immersion heater powered by solar PV is probably the right way to go, but even then, standing losses will account for around 500 kWh each year.

If you are committed to having heating in individual rooms, simple electric wall heaters with thermostats and timers (at £50 each) would do the job on the rare occasions when you need additional heat.

Johnandabby

Robwiz wrote: »

In my opinion, an air source heat pump used for space heating and domestic hot water is the worst option as it's a real (and high capital outlay) compromise asking ASHP technology to heat water to 55º C.

Definitely wouldn't agree with that, but that's why OP needs to appoint someone to go through the design in detail not just collect random comments on this forum.


Even if the ASHP has a COP of 3, it will be cheaper to run than direct electric immersion. The PV link will reduce requirements further. And you could limit the ASHP output to max of 45oC to improve efficiency, and use electric immersion only to heat up to 60oC for legionella prevention cycles.


And there are good financial incentives for ASHPs through the Renewable Heat Incentive scheme, which makes it worth looking into.


As the OP is going to be living in the house then long term running costs have to be considered, not just capital outlay.

Johnandabby

Robwiz wrote: »

Why do you want to heat every individual room separately? Are you really sure that will be necessary in a house as well-insulated as yours?

An external wall U-value of 0.19 and an exposed site needs IMO heat in each room separately, particularly with variations in orientation.


And it's about thermal bridge and air tightness detailing as much as insulation - unless the detailing is drawn, reviewed and closely monitored during construction it can easily double heating requirements. I had a project recently where the contractor supposedly did everything correctly, installed expensive membranes, checked details etc, but then achieved an air test result of more than 5m3/hr.m2...


To provide an even temperature distribution (and prevent the need for individual room heaters) you really need negative thermal bridging values and air tightness of less than 1.

chichikleine

Thank you very much to everybody who has contributed. It clearly is not a straight-forward situation, but is really has been very helpful, as I now know which critical questions I have to ask when meeting with the builder, Energy home Scotland adviser etc.

chichikleine

I had a meeting with a Home Energy Scotland adviser and he suggested a biomass (pellets) boiler, to fire an underfloor-heating system for the ground floor. Any wise words about this idea?;)