Heating & DHW solution sought for a new highly insulated house

[Pugliese]

Trying to decide on the best heating & DHW solution for a new house I am building.

The design of the building is to go for very high levels of airtightness and insulation akin to a Passive Haus.  However the design of the house and windows will mean that PH certification is a step too far.  We will of course require MVHR.

I have been advised that with the majority of the glazing on the back of the house which is SW facing, for heating, we will only require underfloor heating downstairs.  However I am a sort of belt and braces type guy and will probably run the pipes in for over sized rads upstairs but not fit them, and add later if required. Bathrooms will have UF heating and towel rads.

I am a fan of thermal stores, so to feed that do I go for an ASHP linked to the MVHR with solar thermal or would it actually be more economical because of the insulation (low energy requirement) just to go for a gas condensing boiler and solar thermal, as the capital outlay would be a lot less.  I will also have a room sealed wood burner in the living room, although I suspect it will be hardly used, but good back up in case of power cuts.

I would be interested in people’s thoughts and ideas

[billt]

If the insulation really is that good, don't put any CH in at all. In a spell of really cold weather a few electric heaters should be enough to maintain comfort. The relatively high running costs will be massively outweighed by the non existent capital cost. For hot water use the solar thermal with an immersion heater for cloudy days - with very good insulation on the heat store and all pipework.

If you're concerned that the house won't perform as predicted, install the piepwork and leave the choice of heat source until you know how the house performs and can make an informed decision.

[brackwell]

I suggest you read this www.cca.org.nz "designing comfortable homes"  (remembering to reverse N & S)

A house built to this standard will require VERY little heat input,remembering the not insignificant amount of heat put in by people just living there.  Heating will not be a problem and i suggest you concentrate on the DHW (domestic hot water) - perhaps solar thermal with gas boiler.   I would be considering NOT putting any traditional central heating in a house like this, but the problem is that in the UK we do not have much experience of houses built to this standard.

What you need to think about are the thermal storage capacity Ie lots of concrete walls etc and sun shading in summer as the above discusses.

You dont say where you are and there is a big difference between S of England and N of Scotland !

Someone needs to work out the SAP 2009 heating requirements before going any further.

Ken

[Richard Owen]

I'd probably do pretty much what you're suggesting.

I'd probably go for the gas condensing boiler but order the thermal store with lots of extra tappings and immersion slots so that I could add ASHP or direct electric or something later if the economies of various fuel types change.

I hate radiators and the constraints they place on room layouts so for the upstairs, I'd probably put in the tails to drive skirting radiators. Or perhaps not.

We built our extension in a similar way to your plans over ten years ago. I didn't put in any heating upstairs (apart from UFH in the wetrooms and towel rails) and we've not noticed its absence. Even in the depth of last winter, the Mrs would get up in the middle of the night to open the window a crack.

[solar_cambridge]

One downside to not fitting a gas boiler/heating is that future purchasers may see that as a negative, walk away issue. There are some odd folk out there. You will want a gas boiler that will modulate down to just a few kW and has the weather compensation features. Another advantage is that it is much cheaper to heat your hot water with gas. ASHP won't get you high enough water temps in winter, not without electrical immersion boosting.

Solar thermal is a no brainer. If you go for a big beast 300+ litres store and at least 30 tubes you would not need additional boosting for 6 months of the year.  Oversize the tubes and you could reverse run the excess stored energy through the underfloor a la heat dumping style. How much do you want to tinker and fine tune the system or would you even be allowed to by your SWMBO?  

[EccentricAnomaly]

Following on from the previous two replies, which I agree with completely, I'd suggest doing some calculations of the temperatures needed for underfloor heating.

Assuming 15 kWh/m², as per Passivhaus, and assuming that's all used in the three months of winter that would be an average of 15000 / (3 * 30 * 24) ~= 7 W/m². Since a rule of thumb for UFH is 11 W/m²/°C that means your floor will typically be less than 1°C warmer than the room. One of the main points of UFH is the extra comfort from a warm floor but if it's not usually much warmer than the room you don't really get that benefit.

Maybe UFH in the bathroom and a few large radiators in other rooms?

[Richard Owen]

Following on from the previous two replies, which I agree with completely, I'd suggest doing some calculations of the temperatures needed for underfloor heating.

Assuming 15 kWh/m², as per Passivhaus, and assuming that's all used in the three months of winter that would be an average of 15000 / (3 * 30 * 24) ~= 7 W/m². Since a rule of thumb for UFH is 11 W/m²/°C that means your floor will typically be less than 1°C warmer than the room. One of the main points of UFH is the extra comfort from a warm floor but if it's not usually much warmer than the room you don't really get that benefit.

Maybe UFH in the bathroom and a few large radiators in other rooms?

Floor won't be cooler than the room if the floor is the main source of heat. That's because we put things on floors (cupboards, furniture, rugs, .......) that lower the theoretical heating effect.

The dynamics of our system are:

Water in at 23c
Floor at 21c
Room at 18.5c

One of the idiosyncrasies of UFH is that if you heat the room to the temperature you'd feel comfortable with with radiators (say 21c or 22c for a living room) it feels too warm and too stuffy.

We turned it on about a week ago. Lovely gentle warmth with no apparent source when you walk in the room. The floor (terracotta tiles) doesn't feel warm underfoot, but neither does it feel cold. It feels neutral. Standing still in a skirt (I'm told) or a dressing gown generates a lovely warm feeling round the nether regions.

I can't recommend UFH enough. And if you are anywhere near GL15, you're more than welcome to pop over for a coffee and take a look.

[qeipl]

Trying to decide on the best heating & DHW solution for a new house I am building.

...........

I would be interested in people’s thoughts and ideas

Solar thermal feeding a ASHP DHW cylinder with two coils (e.g. the latest version of the Ecocent).
UFH running off the second coil.
ASHP set up to do MVHR.
Electric heaters in depths of winter when solar gain is non-existent.

Search my threads for Ecocent to find more details of my set-up which is as above but without the ST.
Talk to JSHarris on the Green Building Forum who's in exactly the same position as you.

[dhaslam]

I think you are correct to put in underfloor heating downstairs and in bathrooms.  You can space the  pipes  at about 150mm in bathrooms and 300 mm other rooms.  A very well insulated house will hold it's temperature once it is warm but if you get a long period of very dull weather , like this October in Ireland,   the house will gradually lose temperature and other passive heat sources won't make up the difference. Having the underfloor heating come on briefly keeps the temperature fairly even and you don't  even know it is on except for the odd click from the thermostats turning on or off.   North facing rooms will have some need for heat anyway.   

It is probably best to use a gas boiler (and solar) heating the store.   If you use a heat pump someone else is using the gas   to generate  the electricity and  probably about the same amount.


It would be nice to have a small stove in the living room as well.     

[Pugliese]

Thank you everyone for all your posts and ideas, which I have spent some time considering.

Clearly the SAP calculation needs to be done before any hard decisions are made.

Even though we are on the south coast and I have read with admiration on this and the green building forum some of the clever systems that have been designed to improve the performance of ASHP's, I am not convinced that I will be happy with the performance during winter.  I also believe in the KISS principle.  However I think the idea of setting up the thermal store with extra tappings for other heat sources is a sound idea.

So the base design will be U/F downstairs & bathrooms, with towel radiators in bathrooms as well.  Plumbing in place for upstairs heating in case of need.  Thermal store fed by small gas boiler and solar thermal, with option to plumb in other feeds. Room sealed wood burner in living room for back up.

Now the other decision is what type/make of MVHR do I go for and what do people think of the Viking House FiWi system? http://www.viking-house.co.uk/fine-wire-hrv.html

Thanks again for all your help

[bornagain]

Hi,

I am also a newbie who has been watching this and the green building forum for the last couple of years.

We have just (within the last fortnight) moved into our brand new self build house very similar to the one you are building (icf walls, u=0.15, triple glazed windows, u=0.99, 300mm of EPS underfloor and 600mm of fibreglass in the loft)

We have installed underfloor heating downstairs within the very thick concrete and screed slab and no heating upstairs, a 500l Akvatherm Solar Plus thermal store with two coils piped to solar thermal, and directly to a clearview pioneer 5KW boiler stove; at the moment we are using imersion heaters to heat the water - if the numbers work out then we may convert these to economy 7, time will tell.

So far, the temperature in the house has been extremely stable - we commissioned the underfloor heating last week and brought the temperature upto 21 C - and it has not really moved since then; although the weather from Sunday onwards has been very warm.

The back of the house faces south and we intend to make full use of solar gain, I am coming to the conclusion that the underfloor heating on the south side of the house will not get used to any great extent - it will probably go on occassionally when the really cold weather comes - again time will tell.

We have gone down the MVHR route with a Vent Axia Sentinel Kinetic plus -this seems to work very well.

Good luck

Patrick

[Pugliese]

Hi Patrick

Thanks for the reply.  As you can imagine, very interesting.

Couple of questions if I may, what type and size of solar thermal array do you have?

Where is the boiler stove (Clearview - excellent choice imo) located? - the reason I have not planned for a boiler stove is that the location would be in a SW orientated living room and I am worried about over heating.

Thanks and good luck with the new property, must be very exciting/satisfying

Robin

[bornagain]

Robin,

2 Thermomax HP200 x 20 (so 40 tubes) facing near enough dead south, roof pitch 35 degrees.

The back of the house (south side) is the kitchen / dining room which we think we will more or less live in.

The front (north side) contains the living room and study/kids room.

The wood burner is in the living room directly below the thermal store allowing it to thermocycle the hot water upwards; I believe that a wood burner in a well insulated south(ish) facing room would never be used as it would make the room much too hot..

And thanks, it is great to be in; last winter with two kids in a static caravan was not much fun.

Regards

Pat.

[dullnote]

Hi I have UFH the space of the pipe are 100 in bathrooms and kitchen and 150 everywhere else, not a issue. But be aware the house will heat up slowly compared with radiators, on the same it will also cool down as slow. Heat is a comfortable and I do like it.

My issue is I have LPG and it costs a fortune, looking for the  best option.

Facts about house

240m2 detached house two stories, the SAP cals come out with 67 (dont know what this tells me), heat loss 1.14 W/m2K again dont know what this means. Can anyone explain? and the estimated heat for the year is 590GJ/year this is for water and heat.

Thats all the technical bit below is what I know

I have solar DHW panels fitted when house built great never used the boiler from May to mid Sep, 33KW LPG boiler, and I have just had fitted 3KW PV system

Basing the information on last years meter reading IE before PV fitted

Gas used 3604lt used, to convert to KWH 7.08 (according to Calor Gas) equates to 25,516 KWH, electricity 4215KWH used.

This cost me using last year actual readings Gas £1652.12 and Electricity £530.28 Total cost £2182.40.


I am thinking of some sort of heat pump,

For me to break even lets assume the house elecricty does not change I would need to purchase 25,516KWH of electricity to replace the LPG which would cost £2881.52 using my existing tariff, therefore 2881.52/1652.12 Pump would need a COP of 1.744.

If I look at Fit £900 and RHI £700 (read somewhere in these forum estimated return) would give me £1600/ year.

ASHP assume COP 2 and cost £7.5k total energy cost £1971 then the return leaves me paying £30 a month as I am paying £210/ month this would give £180 to pay investment which works out 3.5 years

GSHP Cost £15k COP 3 total energy cost £1490  as above but I would earn £9.10 , Return total £219.10 giving 5.7 years .

I know this is long winded and not sure what I am asking, but could someone explain the SAP info to me, also am I way off on the calcs

Dullnote

[JohnS]

Dullnote

How old is the house and how well insulated is it?  Is it in an exposed location?

I have a similar size house.  It is an Edwardian solid wall house but with a latest standards loft conversion and a bit of internal wall insulation - less than 15% so far. Lots of LED lights etc.  Good central heating controls - ie thermostat with different temperatures at different times.

My energy useage is 24,000 kWh of gas and 3,600kWh of electricity.  Compared to this yours looks very high.  Biggest savings will be acheived with more insulation.