DHW heating in a passive house.

Do-more

I'm going around in circles trying to decide what is my best option for heating DHW in my new build.

Hopefully some kind souls here can give me some direction.

One possibility of course is solar thermal but I am not sure how many months of the year this can provide for most of the DHW needs for a family of four.

I'm not sure if the following data can provide a guideline, it comes from this Solar PV estimation app and relates to my site.

Latitude: 55°20' North,
Longitude: 13°22' East
Nominal power of the PV system: 1kWp
Inclination of modules: 45deg.
Orientation (azimuth) of modules: -45deg.

Fixed angle
Month Ed Em Hd Hm
Jan 0.56 17.4 0.70 21.8
Feb 1.21 33.8 1.55 43.4
Mar 1.91 59.2 2.53 78.3
Apr 3.12 93.5 4.21 126
May 3.81 118 5.31 165
Jun 3.48 105 4.93 148
Jul 3.60 112 5.11 158
Aug 3.13 97.1 4.44 138
Sep 2.31 69.2 3.19 95.6
Oct 1.49 46.3 1.98 61.3
Nov 0.82 24.6 1.05 31.6
Dec 0.44 13.8 0.55 17.1
Year 2.16 65.8 2.97 90.3

Ed: Average daily electricity production from the given system (kWh)
Em: Average monthly electricity production from the given system (kWh)
Hd: Average daily sum of global irradiation per square meter received by the modules of the given system (kWh/m2)
Hm: Average sum of global irradiation per square meter received by the modules of the given system (kWh/m2)

Another possibility is a 4.5kw CO2 air source heat pump which may be suited to DHW heating only but I am not convinced.

An exhaust air heat pump is also a possibility.

I'm not inclined to go for a wood burning solution for a number of reasons and there is no mains gas available.

Planning restrictions rule out wind power.

All opinions welcomed!

BryanF

what sort of energy loading is expected from the phpp and what sort of mvhr system have you installed, as there may be scope to attach a sort -of air-source system. regardless of the above, get the solar HW panels first, it'll provide roughly half you HW requirements but not in the winter, ask your energy consultant to advise you on thermal stores. in winter is also when the ASHP beomes less efficient and PV is not going to do much then either. may i ask why you have ruled out wood pellets or timber gasification boiler? imho after maximising layout/ orientation, building fabric and energy reductions timber should be your first stop

Do-more

The phpp hasn't been done yet, the Architect will only start working on the drawings in the coming week, I'm just trying to get my head around what solutions we will probably be looking at. I also have a meeting scheduled in the Swedish passive house centre next week and am trying to prepare so that I can ask all the right questions!

Total heating load should be 2-2.5kW, MHRV should provide 0.9kW.

Kitchen, hall, utility and bathroom will be tiled surface and I expect we will have a light direct electric loop under these to provide comfort heating on a timer so this should provide the balance of the heating load.

My reluctance to go with wood burning is in relation to the release of carcinogens.

mark2003

You can get a hot water cylinder with its own 3kw ground source heat pump. you just have two gas pipes running 3ft under the ground. roughly costs 20cent a day to heat water for 365 days of the year.

Do-more

mark2003 wrote: »

You can get a hot water cylinder with its own 3kw ground source heat pump. you just have two gas pipes running 3ft under the ground. roughly costs 20cent a day to heat water for 365 days of the year.

Cheers

Would you be good enough to PM me some details please.

sinnerboy

You could keep it very simple . A 90% + efficient 12KW wall mounted oil boiler for hot water and bathroom rads and maybe one or two space heating back up rads will be twice about as powerful as you will need but probably the least expensive capital cost option.

Mothman

My requirement for space heat is very little. I've no rads or underfloor heating. For winter I have a wood burning cooker which heats the water

For rest of year
I use solar backed up by an immersion.

BryanF

tell us more about your concerns over the carcinogens Do-more, is this for health reasons or environmental reasons? seems a bit much to be ruling it out at this stage!

Do-more

BryanF wrote: »

tell us more about your concerns over the carcinogens Do-more, is this for health reasons or environmental reasons? seems a bit much to be ruling it out at this stage!

It's a health issue Bryan concerning carcinogenic particulates in wood smoke. Good quality pellet stoves are much better in this regard than a standard wood burner but it is still an issue.

Some local councils here in Sweden have already placed limits on wood burning in urban areas and in the same way that coal has been outlawed in the past I see it as inevitable that more limits will be placed on wood burning in urban areas in the future.

sinnerboy

The owner of Ireland's 1st PHI certified Passive House has remarked that solid bio fuel ( he himself uses a wood burning stove for winter hot water ) is not the answer for everyone. One needs to be able bodied to use it. Disability arising from an accident or aging can render this method unsuitable.

Do-more

sinnerboy wrote: »

The owner of Ireland's 1st PHI certified Passive House has remarked that solid bio fuel ( he himself uses a wood burning stove for winter hot water ) is not the answer for everyone. One needs to be able bodied to use it. Disability arising from an accident or aging can render this method unsuitable.

Yes there can be quite a bit of work involved in chopping logs, seasoning, storage and loading, but that is not my concern rather I personally don't feel it is proper to subject my neighbours to wood smoke when there is a reasonable prospect that it may pose a health risk.

There is of course also the possibility that any wood/pellet burner would become redundant within a few years.

BryanF

thats very interesting Do-more and what is the swed's preferred heating source inlieu of timber, is all bio-mass included in this? I guess a larger % of their elec is from renewable sources?

here's an interesting book for you that may flag some other health effects in construction materials http://books.google.com/books/about/The_whole_house_book.html?id=yKjgPQAACAAJ

quentingargan

I've seen passive houses fit solar (tubes have a longer operating season and are of more benefit in this situation). If the roof is a bit steeper than normal, that will also help with the seasonality. 45 is pretty close to optimal for spring & autumn. If you back that up with an immersion that only runs off-peak at night, it would probably be the most cost effective solution.

Also, it may ony be a technicality, but you will need something to meet the renewables obligation of Part L. That could be solar PV or something else, but solar thermal would also tick that box for you hopefully..

I would get computer simulations done using the EN12975 certificate info to give you a good estimate of the likely output of a solar thermal system for your house.

BryanF

quentingargan
tell us more about 'computer simulations done using the EN12975 certificate' are talking about the http://re.jrc.ec.europa.eu/pvgis/ ?

Do-more

BryanF wrote: »

thats very interesting Do-more and what is the swed's preferred heating source inlieu of timber, is all bio-mass included in this? I guess a larger % of their elec is from renewable sources?

Timber is a very popular choice of fuel here, primarily in rural homes so I would never see there being an outright ban here, but I do see the possibility in urban areas.

According to this website "In Sweden, heat pumps have a share of 90% in domestic heating and hot water." (referring to new installations I suspect)


I do need to do some modelling of the different options available to compare capital and running costs, so will try to find a local energy consultant to assist in doing that, I visit the Swedish Passive house centre on Tuesday so hopefully they will have some info on energy consultants familiar with the particular demands of energy use in a passive house.

I don't have to worry about the Part L requirements for renewables here in Sweden Quentin and I suspect that the length of the off-season for solar thermal will tip the balance towards some form of heat pump solution particularly as I would be relying on direct electric during the off season. Modelling the costs should provide the answer to that.

Unfortunately the Austrian manufacturer of the ground source water heater mentioned by Mark2003 doesn't seem to have a distributor here but no doubt they are not the only manufacturer of such a solution, I'll just have to ask around.

galwaytt

...heat pump popularity may well be fuelled (sic) by the availability of cheap electricity.

I've had relations from Norway staying with us for the last week, and the only paying 5c/unit for it. Given that sort of pricing, you'd be mad to NOT use an electric-based system.

Do-more

galwaytt wrote: »

...heat pump popularity may well be fuelled (sic) by the availability of cheap electricity.

I've had relations from Norway staying with us for the last week, and the only paying 5c/unit for it. Given that sort of pricing, you'd be mad to NOT use an electric-based system.

Unfortunately the headline rate per unit only tells part of the story. The July price per unit here in Sweden was 4.7 cent + vat @25% however electricity prices fluctuate from month to month according to the spot rate. This page shows you the price per unit exec. VAT month by month back to 2001.

So in the winter months when demand is highest the price can more than double from summer prices.

In addition to that you pay a standing charge to the electricity supplier and another to the network for your electricity connection plus energy tax plus VAT

The house we are renting has no wet heating system just oil filled electric radiators which were the norm here in the 70's and 80's and an air to air heat pump which was retro fitted a few years ago, water heating is an electric immersion.

Looking at our electricity bill for Jan/Feb this year, the total consumption was 2941 kWh for which we paid in total 4890Kr so the actual total price works out at approx. 18 cent per unit.

For May/June when usage was much lower the end price per unit was just over 20 cent per unit because of the greater effect of the standing charges.

This website compares energy prices across the EU and shows that average prices in Sweden are pretty much the same as in Ireland.

quentingargan

BryanF wrote: »

quentingargan
tell us more about 'computer simulations done using the EN12975 certificate' are talking about the http://re.jrc.ec.europa.eu/pvgis/ ?

The EN cert provides information on panels from actual laboratory tests;

zero loss efficiency - How well the panel absorbs light
Heat loss coefficient - How well insulated it is
IAM - The efficiency of the panel at different angles of attack.

There are professional simulations, (e.g. T-Sol) which can use this data combined with geographical location, roof pitch, orientation, distance from cylinder to panel, cylinder size, demand etc., to arrive at a figure for what the solar panel will actually deliver in your situation.

These simulators are generally a lot better than the DEAP software used by SEAI for BER assessments - particularly as they take IAM into account, which DEAP doesn't. Q

BryanF

Do-more wrote: »

It's a health issue Bryan concerning carcinogenic particulates in wood smoke. Good quality pellet stoves are much better in this regard than a standard wood burner but it is still an issue.

Some local councils here in Sweden have already placed limits on wood burning in urban areas and in the same way that coal has been outlawed in the past I see it as inevitable that more limits will be placed on wood burning in urban areas in the future.

Do-more, I dont wish to hark on about this but following a read of your US link, it would seem to me that they are discussing open fires and stoves, which is not the same thing as an effecient gasifacation burner or pellet boiler. from my general understanding of burning wood, if it is done at high temperatures the carcinogens are far less of a concern. If you are not near a gas mains, I can only presume you are relatively rural. the US link and the swed's seem to be saying, inefficient burning of timber in urban areas causes smog and knock on respiratory issues. I would still not rule out using an efficient log burner, although there is some work involved it would negate the majority of cost relating to fluctuating electrical prices.

Do-more

No problem Byran, this website gives a rough comparison of the emissions from various different types of wood burning and as I said myself the emissions from a pellet boiler are considerably less than many other methods of timber burning.

Personally speaking if I was out on the fields and had a small holding I would go for a log gasification boiler, but I will be in the middle of a village of 1200 so would rather not go for wood.

Do-more

I got to speak to a seemingly pretty knowledgeable architect in the passive house centre here during the week and he reckoned that it is very very unlikely that any possible ban on wood burners in urban areas would include wood pellet burners.

So that seems to rule out that part of my concerns at least.

He was suggesting to go with solar and supplement in the winter months with a wood pellet stove with back boiler for water heating. Not sure how that would work out as whenever we would need water heating we would also get some space heating whether we needed it or not.

He made some quick calculations and reckoned we would do it with 20 bags of pellets which I figure would only cost about €100.

The passive house supplier was suggesting to go with solar backed up with direct electric in the winter and have a simple air to air heat pump (costs about €1500 installed here) for what little space heating we will need.

I definitely like the idea of keeping it all simple so the latter option is my most favoured.

Anyway the designer is starting work on the drawings this week so I should have some figures to base some comparisons on shortly.

What do people feel is a reasonable figure for water heating for a family of 4?

The architect in the passive house centre was making his calculations based on an estimate of 3,500kWh p.a.

beyondpassive

You've gone to the trouble of installing a lot of insulation, you have MHRV installed and good solar orientation. Why not have a conventional heating system.

3500kWh for your DHW for your build sounds about right, Solar tubes to meet regs part L (are you building in Ireland) should meet half of that. Space Heating for a passive house is about more than providing for 20 degrees comfort year round. Comfort is a very subjective thing, and two persons perceptions of comfort in a particular environment could be as much as 5 degrees apart. Prob 6degrees for my wife and I.

If Solar is your RES of choice to meet the 10kWh per sq.m renewable s quotient, then you could use some of that to heat your structure by using a large combination buffer tank and some underfloor. To meet the remaining say 2,500kWh of space heat and 2000kWh of hot water you could employ a boiler of some description, mains gas or LPG are a good choice as the boilers and cheap and modulating. Wood chip stove is of course the green choice, also consider a log/pellet hybrid with back boiler. We suggest installing gas now, and in 15 years replace with biomass. Plumb for both scenarios.

So now you have your base load covered, if you want to have some extra 'grunt'. You don't really need it but, it can be useful to have quick ramp up heat available, then you could run a low temp radiator circuit or as we call it a towel rail loop, to give you discretionary heating. You may never use it, but its better to have it in reserve. Climate's a bit wonkey, mother-in-law is a cold creature and we're lucky to get a long weekend in the sun. Besides a towel rail in the hot press combines with Heat recovery extract, is a greener alternative to a dryer or a clotherline.

Of course there are non mechanical systems out there which store excess solar under the slab or in water/PCM stores inter-seasonally to provide space heat, in this case a compact water to air heat pump could be utilised to bump up stored heat to 35 degrees for underfloor and 555 degrees for water and tank. Need to moniter therese over the next winter to see how the stores retain heat through January.

Do-more

Cheers bp, I'm building in the south of Sweden so I don't have any restrictions on having to include renewables in the equation.

What I'm interested in is finding the best solution in terms of lowest capital costs Vs. lowest running costs.

I don't have some higher agenda forcing me to spend 1000 x X in order to save X just because that is the "greenest" solution.

My decision to build passive is because it is financially the best thing for me to do. I've seen estimates here that for my part of Sweden the extra cost to go passive is about 3 - 5% of the total build cost and in fact as I will build with direct labour as I did previously in Ireland I expect to build for significantly less than other build costs in the area.

The Swedish building industry and it's customers are extremely conservative and slow to adopt change, I'm told that there are estimated to be less than 100 single family passive dwellings in the whole of Sweden. (pop. 9M). When I mention that I will build direct labour the first comment is always that I must have a main contractor, otherwise who can I blame if anything goes wrong! Obviously the concept of taking responsibility yourself isn't big here.

Anyway I digress, back to the hot water heating. I have made a comparison of solar radiation between my site and a site just outside of Galway city where I know someone with a solar thermal installation and even though I am at a higher latitude (about the same as North Donegal) I get (slightly) better figures for all bar Nov. Dec. and Jan. so I am pretty confident that solar can provide me with a good chunk of my water heating requirement.

The question is just what the running cost will be in terms of the electrical top up I will need in the winter, spring and autumn months and whether I am not better to employ the capital in an air to water heat pump which will need to run all year round?

beyondpassive wrote: »

Wood chip stove is of course the green choice

If you read back through this thread you will see that on health grounds I would disagree with you that wood burning is the "greenest solution"

Seasonal stores are out of the equation for me both in terms of capital costs and payback. I have spoken directly with someone who has one and even though it has been built to a high standard at huge expense they are experiencing heat losses of about 60%!

A store which is built entirely within the building envelope may work but I don't have the space and the capital costs are still excessive IMO.

beyondpassive

Do-more wrote: »

The question is just what the running cost will be in terms of the electrical top up I will need in the winter, spring and autumn months and whether I am not better to employ the capital in an air to water heat pump which will need to run all year round?

You're combined heat load is about 7,000kWh before solar, including fans. At 18c per kWh, Sweden despite its Hydro, has similar prices to Ireland, http://www.energy.eu/ but surely variable rates make it much cheaper?

Lets say it was 18cent per kWh, thats €1,260, with a heat pump with an average COP of 3. those costs could be brought down towards €400, so you're looking at about a 7 yr payback on day rate electricity.

Best to use a wet system to heat the house as you heat up the structure first. A 12kW heat pump would be oversized but you need to be running the system at a certain power to get the declared efficiencies. With heating supplied via the ventilation system alone, in thermally massive builds the walls and floors can often be below comfort levels and therefore absorb rather than radiate the occupants body heat.

Do-more

Cheers bp if you see in post #17 I discuss how electricity is priced here which is a little different to in Ireland. We pay a "line rental" charge to the network plus a charge per kW for the delivery of the electricity to the house, then we pay the variable rate per unit plus energy tax plus 25% VAT.

If I could keep total yearly electricity usage below 8000kWh on a 16A main fuse I could get a "holiday home" tariff which would reduce the network charges by approx. €286 p.a. but I don't think that is feasible.

The house is a twin wall TF design with walls approx 450mm thick with mineral wool insulation and the sloping roof will be insulated with approx. 500mm of cellulose so the house will not be thermally massive.

Another possibility that I need to investigate further is to use a 500 litre HW storage tank and have a connection to a heat exchanger in the ventilation system to add heat to the house when required on a simple control system.

One thing that works in my favour is that whilst the weather in the area I live in is actually milder than in Ireland for most of the year the insulation requirement to achieve passive standard in my heating zone (Sweden is divided into 3 heating zones) is much higher than in Ireland. As I am in the mildest part of my zone which also must account for houses build several hundred kilometres further North and inland I expect my heating load to be well within the max. 10w/m2 on the coldest day of the year which is the requirement in this zone.

galwaytt

Do-more wrote: »

Unfortunately the headline rate per unit only tells part of the story. The July price per unit here in Sweden was 4.7 cent + vat @25% however electricity prices fluctuate from month to month according to the spot rate. This page shows you the price per unit exec. VAT month by month back to 2001.

So in the winter months when demand is highest the price can more than double from summer prices.

In addition to that you pay a standing charge to the electricity supplier and another to the network for your electricity connection plus energy tax plus VAT

The house we are renting has no wet heating system just oil filled electric radiators which were the norm here in the 70's and 80's and an air to air heat pump which was retro fitted a few years ago, water heating is an electric immersion.

Looking at our electricity bill for Jan/Feb this year, the total consumption was 2941 kWh for which we paid in total 4890Kr so the actual total price works out at approx. 18 cent per unit.

For May/June when usage was much lower the end price per unit was just over 20 cent per unit because of the greater effect of the standing charges.

This website compares energy prices across the EU and shows that average prices in Sweden are pretty much the same as in Ireland.

The prices we have for electricity also exclude standing charges, VAT, carbon tax (!), and we don't have the benefit of any per-unit charges anything like as low as you, so you're still quid's ahead imho.

Do-more

galwaytt wrote: »

The prices we have for electricity also exclude standing charges, VAT, carbon tax (!), and we don't have the benefit of any per-unit charges anything like as low as you, so you're still quid's ahead imho.

Two different ways to skin a cat.

From what I can see on the ESB website the domestic standing charge is €92 a year + VAT @ 13.5% where as my standing charge here is approx. €407 + VAT @ 25% plus a delivery charge of 2.2cent per kW (inc VAT) which doesn't seem to apply in Ireland at all.

The 25% VAT rate applies to the whole bill BTW rather than the 13.5% rate in Ireland.

As I pointed out in my original post the effective rate we pay for electricity is actually slightly higher than what you pay in Ireland.

Quids ahead you say?

BigGeorge

Just wrapping up our PH build, heating & DHW system as follow:

• >10sqm of solar thermal panels hooked up to a 1500lt stratified tank
• in line water to air duct heater on MHRV & a few rads
• 12 kw modulating gas boiler ( alternatively could easily be oil) connected to solar tank

System needs little manual intervention ( ie no pellet loading) & low capex. The low cost & reliability of gas and oil boilers really is hard to bet I believe. Key thing I think is to keep the system simple for different elements are not working against each other.

Pretty similar to what sinnerboy has suggested

quentingargan

BigGeorge wrote: »

Just wrapping up our PH build, heating & DHW system as follow:

• >10sqm of solar thermal panels hooked up to a 1500lt stratified tank
• in line water to air duct heater on MHRV & a few rads
• 12 kw modulating gas boiler ( alternatively could easily be oil) connected to solar tank

System needs little manual intervention ( ie no pellet loading) & low capex. The low cost & reliability of gas and oil boilers really is hard to bet I believe. Key thing I think is to keep the system simple for different elements are not working against each other.

Pretty similar to what sinnerboy has suggested

Good on yer. I would possibly suggest also a heat dump to outside the building as an option when the tank is up to full temperature. This will happen in the summer, and you won't want that heat in the house.

It will be interesting to see if the solar thermal makes a useful contribution to space heating via the MHRV. In the months of Nov to Feb, it seldom provides hot water for a family, but if your requirement is at low temperatures only, you may find it economical to use the solar to heat the house, and run the gas to heat the water.

Do-more

I've now had the PHPP done for the house so have some figure now to work to. There remains to be some revision done to the design but at this point it doesn't meet German PHI levels.

There are a couple of factors which undoubtedly contribute to that, for example the MHRV unit we are using is not PHI certified and neither are the our outside doors. I can't find our Norwegian windows on the PHI list either.

However there is almost zero focus on German PHI certification here in Sweden particularly as there will be a Swedish Passive house standard introduced here next year. There are currently no single family dwellings in Sweden on the PHI database.

I know that our MHRV and windows are certified for the Swedish standard and I have already sent our PHPP to the Swedish passive house centre to see how it will perform under their calculations.

Anyway as it stands the main figures for our house are:

Exterior wall 0.098 W/(m²K)
Floor slab 0.109 W/(m²K)
Roof 0.082 W/(m²K)
Doors 0.587 W/(m²K)
Windows are averaging around 1.00 W/(m²K) for the complete unit, the glazing is 0.55 W/(m²K).

With the penalties for the uncertified items the heating load is coming to 12 W/m² against the target of 10 W/m² and the specific space heating demand is 23 kWh/(m2a) against a target of 15 kWh/(m2a).

At this point I don't know what these figure will be without the penalties but I am hoping that the Swedish Passive house centre will let me know if I could achieve Swedish passive house certification.

At this point I don't see any economic sense in paying considerably more for certified products as I can't see their being a viable pay back. But I would be delighted to hear other peoples comments.

As for sizing the space and DHW heating systems the annual heating demand is 4509 kWh/a with a heating load of 2342 W.

The DHW demand is calculated at 4129 kWh/a with 48% of that contributed by 8 solar tubes.

I'm think of an air to air heat pump to take care of the space heating, it's tested at a COP of 4.59 but assuming a more likely real world COP of 2.5 that would give an annual running cost of approx. €360.

With an 8 tube solar installation and the balance being provided by an electric immersion the annual running cost should be around €430. But the figures don't show any month where solar provides 100% of the DHW demand so I can probably count on sticking in 12 tubes instead which should reduce the balance required by direct electric significantly.

Of course the PHPP is suggesting a demand of 4129 kWh when my previous estimates were based on a demand of 3500kWh. so maybe I don't need that much hot water at all?

I should probably price a small wood pellet boiler and see how that compares in terms of capital and running costs if I use it for all DHW demand and for space heating with a hot water duct heater in the MHRV.

Decisions, decisions.

fclauson

As you do this - make sure you get a DEAP/BER calc done - make sure your panels deliver the required 10Kw/M2 Part L

Passive houses are not always easy to comply with Part L

Do-more

fclauson wrote: »

As you do this - make sure you get a DEAP/BER calc done - make sure your panels deliver the required 10Kw/M2 Part L

Passive houses are not always easy to comply with Part L

Cheers fc but as I am building in Sweden I thankfully don't have to worry about the Part L requirements.

beyondpassive

There is a few tricks to get improvements, such as increasing the treated floor area, and bringing windows down to floor level, you could also line the internal reveals and use high transmittance low U value glass. Maybe use Softboard outside the racking board if budget allows.

As an alternative method to get your heat demand below 15kWh/m2.a You could consider dumping excess summer solar into the soil which could be contained by skirt insulation around the foundations or raft. This heat loss would be mostly into the house above, autumn and spring solar could be stored in the floor slab if this is made deeper. This could reduce the heat demand if you could keep the soil temp under the house up towards 20 degrees through January. Depends on solar irradiance and soil types and the design of the sub soil heat exchanger, This system has been used in Alaka but with about 80m2 of solar panels.

Do-more

Thanks bp, I've looked at these seasonal stores as they are used in the US and Canada but the problem I have with solutions like this is the huge investment required in installing such a system, 80m2 of solar panels, ground coils, and extra insulation and then whatever the running costs will be for circulation pumps and maintenance etc. all to save an estimated €360 a year which the heat pump should cost me to run.

Add in the fact that there is no local knowledge and no guarantee that it will actually wipe out my heating requirements and I'm afraid that this solution is not for me.

Do-more

I now have some revised figures for the PHPP based an alternative sizes of solar panels.

The original PHPP was calculated on the basis of 4.4m² of solar panels but some alternatives were tested in the new calculation and 7m² will give us 65% of annual DHW demand and 8m² will give us 69%.

Using 8m² of solar panels reduces our expected DHW costs to approx. €265p.a. which is of course significantly cheaper than the €430p.a. I had estimated with the original 4.4m² of solar.

The space heating estimate of course remains unchanged at an estimated €360 p.a. using an air to air heat pump.

I need to do some payback estimates for different scenarios to be 100% sure, but it seems clear that for the lowest capital cost vs lowest running costs the decision will be to go with 7-8m² of solar panels for DHW, with the balance provided by a direct electric immersion heater and for space heating we will go with a simple air to air heat pump.

In terms of getting the overall PHPP to a level we could certify to German PHI standards the architect has kindly done some extra calculations to demonstrate where the highest heat losses are occuring:



This clearly shows that it is the windows which are letting me down but as the increased cost of specifying PHI certified windows would be enormous there is absolutely no justification for it in economic terms.

A much sounder investment will be some decent heavy curtains to be drawn at night in the winter months!

kboc

quentingargan wrote: »

Good on yer. I would possibly suggest also a heat dump to outside the building as an option when the tank is up to full temperature. This will happen in the summer, and you won't want that heat in the house.

It will be interesting to see if the solar thermal makes a useful contribution to space heating via the MHRV. In the months of Nov to Feb, it seldom provides hot water for a family, but if your requirement is at low temperatures only, you may find it economical to use the solar to heat the house, and run the gas to heat the water.

What are these?
Any www's that I can look them up on?
Are they cost effective in pass house?

quentingargan

I think whether you get any solar gain via MHRV is hard to find real data on. For example, on sunny cold winter days, it may offer some benefit, whereas if you have dull grey days, it won't.

It is counter-intuitive to use solar for heating at all because most passive designs already include solar passive heating in the design of the building envelope. Indeed, the more passive your house is, the shorter the period over which any sort of solar heating would provide any gains.

When I say "it would be interesting" I mean, "it would be experimental", not "it would be cost effective"! I don't think it would be cost effective. I would personally stick to solar heating the water. I remain unconvinced about the benefits of solar space heating, except possibly in a poorly insulated house which has heat requirements at night time in the late spring & early autumn.

Do-more

Going by the text in bold I presume that kboc is enquiring about an external heat dump Quentin.

My solution for this kboc is to use a cheap steel frame swimming pool in the back garden as the heat dump, the kids will be delighted!

quentingargan

Do-more wrote: »

Going by the text in bold I presume that kboc is enquiring about an external heat dump Quentin.

DOH!

Just radiators under the eaves. They will only occasionally come into use, but when they do, they prevent the solar fluid going into stagnantion and overheating. When that happens, you can change the nature of the antifreeze, and you put a lot of pressure on the system and shorten its life. So yes, I think it is cost effective.

But I like the swimming pool idea too.

Do-more

quentingargan wrote: »

Just radiators under the eaves.

How do you plumb these to protect them from freezing and bursting in the Winter?

quentingargan

Do-more wrote: »

How do you plumb these to protect them from freezing and bursting in the Winter?

The solar fluid usually has propylene glycol in it as an antifreeze, so no problem there.

Do-more

Ah OK so the dump is plumbed on the solar side, I had wrongly assumed that it was plumbed to dump excess temperature from the hot water store. It of course makes much more sense to have it on the solar side, my bad. Thanks.

quentingargan

Do-more wrote: »

Ah OK so the dump is plumbed on the solar side, I had wrongly assumed that it was plumbed to dump excess temperature from the hot water store. It of course makes much more sense to have it on the solar side, my bad. Thanks.

Well, some people do put a pump on the top coil of the DHW cylinder to circulate the heat through the rads as you suggest, but generally in a passive house, when there is too much hot water, you won't be wanting heat in the house...

beyondpassive

quentingargan wrote: »

Well, some people do put a pump on the top coil of the DHW cylinder to circulate the heat through the rads as you suggest, but generally in a passive house, when there is too much hot water, you won't be wanting heat in the house...

With a 750 or 1000L stratified heat store you can feed the underfloor from the middle of the tank which should sit at 36 degrees for long periods during spring and autumn, with your 45 degree south facing array of 6-8kWh/m2.a

Do-more

Cheers bp, I'm just waiting on some replies back from my architect and a supplier before I can start to make any decisions.

I won't have any underfloor heating in the house in any case.

One option is 8m2 of solar thermal with an air to air heat pump and immersion for the balance of my requirements.

The other possibility is solar thermal plus a wood pellet boiler supplying the balance of my hot water and feeding a hot water duct heater in the hrv duct.

The answers I'm waiting on are whether it is possible to add 2-2.5kW of heat to the house through the ventilation system and if so what the increased capital cost will be and whether it can justified?

The supplier emailed me today to say he would ring on Tues or Weds with a proposal so hopefully I will be a step closer then.

CaraK

beyondpassive wrote: »

There is a few tricks to get improvements, such as increasing the treated floor area, and bringing windows down to floor level, you could also line the internal reveals and use high transmittance low U value glass. Maybe use Softboard outside the racking board if budget allows.

As an alternative method to get your heat demand below 15kWh/m2.a You could consider dumping excess summer solar into the soil which could be contained by skirt insulation around the foundations or raft. This heat loss would be mostly into the house above, autumn and spring solar could be stored in the floor slab if this is made deeper. This could reduce the heat demand if you could keep the soil temp under the house up towards 20 degrees through January. Depends on solar irradiance and soil types and the design of the sub soil heat exchanger, This system has been used in Alaka but with about 80m2 of solar panels.

Apologies for reviving an old thread but I was researching solar heat dump

Would a simpler solution to the ground coil be to lay insulated UFH pipes around the perimeter of the house before footpaths are laid? Put them on separate zone or will they just freeze eventually and burst?

fclauson

CaraK wrote: »

Apologies for reviving an old thread but I was researching solar heat dump

Would a simpler solution to the ground coil be to lay insulated UFH pipes around the perimeter of the house before footpaths are laid? Put them on separate zone or will they just freeze eventually and burst?

Madness - why heat the outside of the house !!!

Build right, airtight, insulate right

CaraK

fclauson wrote: »

Madness - why heat the outside of the house !!!

Build right, airtight, insulate right

I know it's madness might make sense in Boston no shovelling the footpaths. however the picture I was referring to is the one with a ground coil heat dump hence my suggestion as the thoughts of having to get digger in for the ground coil may be enough to put people off even considering it,I know it would put me off



Here's a detail I seen where the outside footpath has insulation also. Geocell a glass based aggregate that is also an insulator

air

Surely PV and a heat pump water heater makes a lot more sense. No issues with excess summer production and you can make use of it for other purposes in the house. Should be cost competitive with solar thermal too.