Anyone offer any advise for a new build in the UK. Question is how to provide space heating without an onerous capital investment? Key parameters: 250m2 traditional block house; u-value Walls, roof and floor < 0.15, triple glazing u-value 0.7; orientation solar-gain friendly to the S; mechanical heat recovery integrated with splat thermal (hot water elevating temperature in air intake plenum by 3 deg to elevate circulating air temp). So aside from colder, sunless winter days our space-heating and hot water needs are met through high insulation levels, high airtightness levels, passive solar gain - all upfront investments. After that context the Q is what is the optimal space heating source for those cold summer nights and winter sunless days? Is the answer a small (~10kw) attractive, relatively low investment cost (£2k), low running cost indoor wood pellet stove diverting much of it's output to a thermal store with the HW distributed via a few radiators and/or some underfloor heating in choice locations? Sorry for the essay ...

There are very few pellet stoves with hydronic output carry the necessary safety certifications to be legally installed in much of the US (and they command a premium price well in excess of£2k) but I suppose they have become pretty common in the UK(?). Here the selection is limited, and I haven't seen any as small as 10kw output.

For heating loads that are under 5kw at typical UK design temps the R744-refrigerant hydronic output heat pumps seem like a decent approach, but I don't have sufficient installed-cost information to compare it to wood-boilers & hydronic-output pellet stoves.

Air-to-air R410A refrigerant ductless heat pumps aren't outrageously expensive either, and work just fine in very-low-U homes too, but they don't provide potable hot water. Installed cost for a ~5kw could easily be in the same price range as a hydronic pellet stove.

Electricity (and heat pump performance) vs. pellets vary a lot from region to region, country to country, but efficiency of ductless air source heat pumps is pretty good in most UK climates. The carbon-cleanliness of the UK power sources still leave a lot to be desired, but it's improving over time.

Thanks for those useful comments. As a non-expert in these technologies and unable to actually experience/anticipate what the final space-heating demand will be (we are just about to construct) the conflicting advice from 'experts' (who want to sell their wares), doesn't help. Even the most modest recommendations seem to plump for either full house underfloor/radiators CH system using air-air (pump, hardware and fitting £10k), geothermal (£10k) or wood pellet - all with underfloor and/or radiators and all requiring a £10k investment. It smells of overkill frankly. Which is why I think a fast-response, modest capital investment, fairly minimal hassle, modest running costs (efficient and won't be needed all that much) in-house wood pellet boiler is the ticket. There are a number of European manufacturers making pellet stoves < > 10kw which are diverting the highest % of their heat towards hot water and a smaller % into the room in which they are located (typical ratio of 80:20). Limited radiators, a small area of underfloor and a pellet stove all in might come in at < half (5£k) of the suggestions I've outlined above. That's enough for a small bit of PV solar...

Les, I am familiar with a number of really good heating engineers in the UK, depending on where you are. I'm not sure how to contact you to give you names so feel free to contact me.

Sorry, I am a bit unclear on your post.

What proportion of your space heating needs are you expecting to be covered by the passive solar features?

And, did you specify an energy source for the "hot water" other than the pellet stove you suggested?

Solar in the U.K. yah right.

First, the availability and cost per unit of fuel in your particular local. Triple pane in the U.K. maybe, but cost/benefit would probably lead in another direction. Radiant floors with ground source heat pumps can be a feasible solution if the gov't. pays most of it and the electricity is not beyond the pale.

As Dana suggests, a air-to-air heat pump works in a good part of the world, as we have specified them in installations from Canada to Argentina. This in spite of the fact that we specialize in radiant floor heating and are addicted to condensing boilers.

Looking at the weather for London, with barely 1% of the year at 79°F cooling is not a priority.

For really well insulated homes, you will find that radiant floors will not be particularly warm, save in the coldest weather, (just below freezing in most of the U.K. on occasion), but is non-the-less and efficient way to transfer heat.

With proper insulation below a slab-on-grade radiant floor or even with panel radiators, comfort is a given.

We analyze local assets and right specifications for homes no matter where you live. But, the answers are in the various proposals if the math is fairly compared. We generally say, insulate and condensate, especially where natural gas is available.

You will get much better answers here than in a U.S. chatroom: http://www.greenbuildingforum.co.uk/forum114/?CategoryID=22
My thoughts anyway. If you want a pellet stove for ease of operation then a heat bank is redundant (a large one anyway.) Given a small enough heat load, a wood stove boiler in combination with a heat bank could do the job in a single full-bore burn each day, or less if the sun is shining.

Posted By BadgerBoilerMN on 14 May 2012 09:57 PM
Solar in the U.K. yah right.

First, the availability and cost per unit of fuel in your particular local. Triple pane in the U.K. maybe, but cost/benefit would probably lead in another direction. Radiant floors with ground source heat pumps can be a feasible solution if the gov't. pays most of it and the electricity is not beyond the pale.

As Dana suggests, a air-to-air heat pump works in a good part of the world, as we have specified them in installations from Canada to Argentina. This in spite of the fact that we specialize in radiant floor heating and are addicted to condensing boilers.

Looking at the weather for London, with barely 1% of the year at 79°F cooling is not a priority.

For really well insulated homes, you will find that radiant floors will not be particularly warm, save in the coldest weather, (just below freezing in most of the U.K. on occasion), but is non-the-less and efficient way to transfer heat.

With proper insulation below a slab-on-grade radiant floor or even with panel radiators, comfort is a given.

We analyze local assets and right specifications for homes no matter where you live. But, the answers are in the various proposals if the math is fairly compared. We generally say, insulate and condensate, especially where natural gas is available.

I know a few people in the UK who, surprisingly, heat almost all their hot water with solar, and not an oversized system either.

 If you look at the temps in the northern part you can get -20C for some pretty long spells so there will always be a need some electric backup to an ASHP.

The Brits make more use of solar hot water for space heatiung than we do. When you use a heat storage tank or heat bank, solar can contribute incremental gains year round and a majority of the heat in shoulder seasons. The value in the latter is less wood to schlepp as much as overall energy savings. In a heat bank approach, you can tie together heat pumps, solar, wood fired or fossil fuel fired boilers or any combination thereof.

forgot the link: http://heatweb.com/

Posted By MikeSolar on 15 May 2012 07:49 PM

I know a few people in the UK who, surprisingly, heat almost all their hot water with solar, and not an oversized system either.

 If you look at the temps in the northern part you can get -20C for some pretty long spells so there will always be a need some electric backup to an ASHP.

I looked- couldn't find any location in the UK that has even remotely that kind of weather, (even for the 50-year lows)- can you name a city where that actually happens? (Maybe some higher-altitude place in Scotland? I just couldn't find it.)  The moderation of temperatures of being surrounded by water (water warmed by North American Gulf Stream no less) does a lot for keeping the minimum temps out of negative double-digits C nearly all the time.

In a high-R/low-U house with any reasonable thermal mass coasting through a night where it hit -20C without backup wouldn't necessarily be a disaster.  Even under higher-humidity cold weather most have reasonable output down to -10C.

In most of the UK a high efficiency ductless with variable speed inverter drive and variable refrigerant volume would have a seasonal average coefficient of performance (COP, sometimes called seasonal performance factor or SPF) in the high-3s, maybe even the low-4s for well insulated house with extremely low heat loads, making it comparable to ground source heat pump performance at a much lower installed cost.

Yes they would be in Northern Scotland. Here is a link to the a forum where I talk to a lot of Brits, and others, about their HP woes. On more than one occasion the discussion turned to the current weather and some of the people said it was hitting -20. -10c was pretty normal at some times of year.

 http://www.refrigeration-engineer.com/forums/forumdisplay.php?78-Heat-Pumps

It must have been last winter because i don't see any abnormally low temps this winter, unless you are in Poland.

A temp of -10C for overnight lows during coldest cold snaps in cooler parts of the UK, sure, but -20C on even a once a decade frequency I won't believe without some documentation, and surely  "...-20C for some pretty long spells..." would need some pretty solid evidence before designing for that, given the outside design temps for UK cities.  

The 99th percentile outside design temps for cities in Scotland are still in low negative single digits C, which is a heluva lot warmer than -20C.   See table 2.4 on page 2-5 (p. 50 in .pdf pagination) in the CIBSE Guidebook-A  (the sterling standard for heating system design in the UK.)  Designing a heating system for -20C anywhere in the UK would border on criminal malpractice.

The all time record low for any location in the UK was -27C, (a temperature at which a Mitsubishi H2i series ductless mini-split can still deliver over 70% of rated capacity), and even on that day the daily high was above -16C, given that the all time national record lowest-high was -15.9C, which occurred on a different date & place than the all time record low.

[edited to add] It looks like it DID make it down to -13C in (all time UK cold record temperature city of) Braemar up in the Cairngorms for an hour before dawn on 7 February this year,  but it was up to 0C before noon that day:

http://weatherspark.com/#!dashboard...er/Braemar

I suppose a windswept mountaintop weather station near there might register -20C once or twice a year, but probably not where anybody lives.

Posted By Dana1 on 16 May 2012 03:00 PM
A temp of -10C for overnight lows during coldest cold snaps in cooler parts of the UK, sure, but -20C on even a once a decade frequency I won't believe without some documentation, and surely  "...-20C for some pretty long spells..." would need some pretty solid evidence before designing for that, given the outside design temps for UK cities.  

The 99th percentile outside design temps for cities in Scotland are still in low negative single digits C, which is a heluva lot warmer than -20C.   See table 2.4 on page 2-5 (p. 50 in .pdf pagination) in the CIBSE Guidebook-A  (the sterling standard for heating system design in the UK.)  Designing a heating system for -20C anywhere in the UK would border on criminal malpractice.

The all time record low for any location in the UK was -27C, (a temperature at which a Mitsubishi H2i series ductless mini-split can still deliver over 70% of rated capacity), and even on that day the daily high was above -16C, given that the all time national record lowest-high was -15.9C, which occurred on a different date & place than the all time record low.

[edited to add] It looks like it DID make it down to -13C in (all time UK cold record temperature city of) Braemar up in the Cairngorms for an hour before dawn on 7 February this year,  but it was up to 0C before noon that day:

http://weatherspark.com/#!dashboard...er/Braemar

I suppose a windswept mountaintop weather station near there might register -20C once or twice a year, but probably not where anybody lives.

I didn't document it. I was part of a conversation but I thought it could be feasible. I suppose I could be a bit clearer when I post.

The real point of most of the conversations there were about the shortcomings of the Japanese type evaporators which have really tight fin spacing and tend not to be installed in a way that they can drain during defrost. Lots of blocks of ice.


Weatherspark is quite a good website, BTW.

I have multiple relatives heating homes with Japanese ductless mini-splits in climates somewhat cooler than the UK, with comparable or higher wintertime dew points who haven't reported condensate or defrost issues, but it's a small sample. There are thousands of installations being monitored under a pilot study being conducted for the US D.O.E. through the Bonneville Power Administration in WA/OR/ID/MT where the (solicited surveyed & reported) occupant/owner satisfaction rates are extremely high (over 90%) which makes me feel safe recommending them for a near-PassiveHouse home in the somewhat warmer UK climate. (The winter temperatures & humidity in Braemar are comparable to Vancouver or Seattle and most of the UK is warmer than Braemar.)

Weatherspark is relatively new, (still in beta-release) but is an AMAZING resource for getting a quick read on local climates and weather, comparing climates, and for estimating local heating & cooling design temps, etc. I use it almost daily.

Alas, forced air (aka warm air in the UK) is a diminishingly small piece of hvac in England, and in the continent as a whole. http://www.homebuilding.co.uk/advice/key-choices/heating/how-to-choose-central-heating-system So the OP's choice of backup heat is constrained by his ability to find a contractor familiar with air/air heat pumps as opposed to air/water. One hopes that the OP has already departed for greenbuildingforum.co.uk.

Mini-splits from all of the big Japanese vendors are available in the UK, and in a high-R/low-U "near passivehouse" building there's no point to radiant floors or radiator distribution- point-source is good enough. If it's a 2-story doored off it might or might not call for a 2-head multi-split, which could handle almost any 250 meter layouts, but even more so for a building designed for low energy use. Being clever about the ventilation duct source/returns is more than sufficient for balancing up room-to-room differences.

If it works in Japan on less-insulated (sometime UN-insulated) homes, surely it works on a low-U building the UK. Sendai is colder on average than Braemar and also gets down to the -10C range every winter, Osaka winter averages & peaks are similar to those in Bristol, etc. I spent a mid-winter week in a circa 1980s 2-story home in Kochi that was heated solely by a kerosene wall-furnace heater on the first floor and it was perfectly comfortable. A 1-head minisplit would have been at least as cozy.

The notion of "central heating system" needs to be revisited in high efficiency homes in temperate climates, since the rationale for needing to distribute the heat mechanically no longer exists (or at least not to nearly the same degree.) The PassivHaus approach is to do all heat distribution via the ventilation air, but even that is but a convenience that takes advantage of the necessary ventilation ducting. In a low-U home with point-source heating, putting the ventilation sources in the space with the heater and the ventilation exhausts in the other rooms does a pretty good job of balancing room to room temperatures with or without ducts.

In a low-U home in the UK that has a lot of passive solar the outdoor temp at which the balance point between heating/cooling mode is likely to be about 12C, and having a heating/cooling ductless may prove to be a better choice than the traditional hydronic heating approach for higher-U homes.

Just guessing here, but one explanation why the brits dallied briefly with hot air in the 60s and 70s and went right back to hot water is that they prefer radiant heat (as do I.) The OP wants to heat water. What say we let him?

The title of the thread being: Space heating solutions in a near-passive house; differentiating between the right answer and sales talk..

Radiant heat in standard construction using code levels of insulation (or even code-U/2) offers a lot in comfort but it offers nothing in a home near-passive house levels of insulation when the floor temp never reaches 22C even at design condition. It is decidedly not the "right answer" when it doubles or triples the cost of the heating system for an unmeasurable boost in efficiency. Distributed/zoned heating systems also make little sense in super-insulated houses when the design of the ventilation can even out room-to-room temperature differences too.

Point source heating in a super-insulated house offers more comfort since at design condition the heat emitter will be at or above body temp, so there's at least one place in the house with the cozy "next to the radiator" kind of feel.  A superinsulated zoned house with distributed panel radiators delivering design day heat with 25C water or radiant floors that never get warmer than 21.5C have no comfort advantage (and even some disadvantage) over heating the same home with a tiny pellet-stove or a mini-split slightly overheating one space.

The O.P. will of course do whatever he likes, but since he is soliciting an opinion for the right answer it's important to point out that "business-as-usual" isn't the right answer in an unconventionally low-U house. In some other 250m house a high kw pellet boiler with under-floor heating & thermal store would make more sense than in a very high performance building envelope.  Passive house peak loads are typically under 2kw, but even at 3-4kw hydronic heating is pointless, but there are many low cost mini-splits that can handle a 2-6kw loads and modulate their output down to 1kw, for a very stable temperature, "systems" that cost less than just the radiation and thermal store for a conventional low-temp hydronic solution.

I'm sorta confused by the "near-passive house" description. Is the OP talking about high mass walls and ceiling at better than R38 and windows up at R8?

Do you shoot for passive house standards and fall short, or how does that come about? Is that typical UK construction or something that is done to utilize a particular heating plant or strategy?