New build - heat, ventilation and hot water

liamdenn

Hi All
Just want to run this by you all and see what you think.
I have been mulling over the pros and cons of a passive house for our own situation.
The considerations for us are as follows:
1.We want a well insulated home with low running costs
2.We want to be as self suffient as possible and not be relient on oil prices etc. I want to take advantage of a free source of wood to heat the house.
3. We want a low tech solution
4. We want a "traditional" looking house.A simple rectangle and not open plan. So a big kitchen, and then a sitting room and playroom. 4 bedrooms upstairs. Footprint of not more than 1900 square feet.
Ok so that the brief!!!!

Now My first worry is that I am not comfortable with MRHV ( I know, I know I will be told I am being silly). My concerns are twofold. One is that I am trying to stay low tech and hopefully avoid expensive maintence etc down the road. Secondly as this is relativly new technology I have spoken to people in industry who use the same sort of technology(in food preperation etc). They all said the same thing. How are you going to get to the pipes if something goes wrong (to clean them for example) and secondly how will you know something has gone wrong. What if something as simple as a mouse gets in and dies, a nasty fungus grows on him and is blown around the house forever more. You will never know!
I am also concerned that if we go to passive standard a stove with backboiler would throw out too much heat into the room.

So allowing for those fears I have come up with the follow solutions
1. DCV instead of MHRV. A low tech system that will simply allow air into a room when the moisture level in the air reaches a certain level. This is not mechanical system which ticks the box for me
2. Install an air source heat pump in the centre of the house
3. Install a stove with back boiler to rads and for DHW.
4. solar panels for DHW also.
5. Aiming for something like 25KW per m2
instead of the 15KW required for passive house standard


So what you guys think? Am I being mad or would this be an afordable, sensible, cheap to run and green system??

heinbloed

I would say you better employ an energy advisor. Or a civil engineer or a heating engineer.
Bring the complete, detailed construction drawings and ask for a signed/guaranteed expertise.
Air sourced heatpumps are noisy and produce condensation, are a mould breeding place. In the interest of hygene they're not allowed to be put into a habitated space. Unless working the other way around, a fridge or freezer or air conditioner.

liamdenn

Thanks for the reply Heinbloed.
I should have added that I am still at a very early stage!!
The way I am approaching this is to sort out these elements and then design the house around it rather than trying to fit them into a design which might not suit.
Just curious as to what other people think.
I am surprised at the comments about the air source heat pump. I had looked the panasonic inverter NE9-SPP.

beyondpassive

Hi Liam,

It sounds like you are doing everything right, compact design and a priority on minimising fabric heat loss. It shouldn't be difficult for you to aim for say 20kWh/sq.m/annum for space heating. You'll find the PHPP tool great for playing around with various combinations of specification to find the right level of performance for your building form and site and to suit your budget. The BER isn't atall acurate for estimating running costs.

I can't see how a mouse would get into MHRV system, and even if you did, you know pretty soon something had died in your ventilation system. I wouldn't get too hung up on any perceived risks with MHRV, there are a few, smoke baffles, noise attenuation, stove smoke backdraft, chill factor from moving air, bulkheads and box outs, frost in the air supply duct etc. The good installations will address these in design and provide you with info on how to maintain the units or else you can have a maintainance contract. Cars have a forced air ventilation system and equally, these ducts needs a service every few years, MHRV is fairly simple really, Its just 2 fans and four filters, but the benefits from installing such a system are profound,

If you find you can't overcome your reluctance to use MHRV, there is a sytem just coming on the market for a decentralised heat recovery ventilation system that can be placed in the wall or incorporated into a window. The call it deventer or FIWIHEX in holland, (fine wire heat exchanger) and its an option for those going near passive and dont want duct runs.

The Heating question is a can of worms. Solar with solid fuel room stove and backboiler is a very slow responce option and requires a lot of choppin, haulin and loadin, the outputs with our timber are about half the rated output claimed by the manufacturer. Heating a few rads may be no problem but heating a cylinder may be an issue. For what it worth why not put in an oil boiler. Oil is cheap at the moment and its better to put it in now and have it as back up. In the future you can install a wood chip boiler or even a heat pump, if and when they become cost effective options. The cylinder say a 1000L, can act as a buffer tank for solar and stove and you could possibly use a small heat pump to regulate heat from the tank and put it into underfloor. You only need underfloor to tiles area as the centralised ventilation system will evenly distribute the heat.

In the mean time your right to concentrate on the demand side and reduce the amount of waste. You'll find you'll need to concentrate on eliminating the massive cold bridges at rising wall and eaves that you get in Irish construction. You'll think about airtightness and also thermal inertia.

DCV isnt a ventilation system, it just closes off holes in the walls. I wouldn't even consider it. Are you designing the building yourself, you didn't mention any professionals involved?

liamdenn

Hi Beyondpassive,
Thanks a million for the reply, some really great stuff.
To answer your last question first. Although I have no expierence in such things I work with ppl who do and bounce ideas off them. I will engage a professional in this area ( another can of worms as to who is best suited) when the time comes but I feel that I really need to understand exactly what all the options are and the pros and cons of them. Then the pro can get on with doing the "sums" regarding space heat requirment etc.
The reason I was thinking of a high KW/m2 was twofold. One is that the DCV will impact negativly on it and the second is the room with the stove will over heat. Is that crazy talk from me?
The reason for being stuck on the stove is that I can use free wood and I think it is probably a good thing to have to do some outdoor hard work once in a while.
I love the idea of the ductless mhrv, i have seen one being promoted with one of the passive house companies.
I would have also included an immersion for the water to top it up when needed and to make sure i can raise the temp to 60oC.

Pete_Cavan

If you are thinking of installing an air source heat pump here is my experience of them. We have an air to water heat pump and towards the end of last year we had a new control panel installed which allows the cylinder to be heated at night and space heating is given priority during the day. Basically the system doesnt have to work as hard during the day to do both water and space heating. Of course that means we only have a cylinder of hot water to last us all day, but we have a combi boiler so that can heat cold water instantly, or water pre-heated by heat pump and deliver it to taps etc. (just means you have to wait a minute or two for water to be heated and make its way around the system to the tap).

We also had a weather compensator stat fitted outside which turns off the heat pump when temperature outside drops below three degrees. Air to water obviously takes heat from the air so when its cold outside it cant produce enough heat but it tries anyway, or did before the stat was fitted. It just means it does not waste electricity when it too cold to work. The combi boiler mentioned earlier takes over then and does everything when heat pump is not being used.

Personally I think this is the best solution (although im sure many will disagree). But without getting too technical, it offers the renewable energy source you want, its fairly simple; same internal plumbing (cylinder, rads, etc.) as traditional systems just with a different heat source installed in garage/boiler room, used for both DHW and space heating, easily maintained and has a fossil fuel backup in case something goes wrong (makes sense to have a backup or supplementary system). Ticked most if not all the boxes so far?

Im not sure how beneficial solar panels would be to this system because they can only realy be used to pre-heat the cylinder but the heat pump is doing that all ready. Same with the stove with back boiler to heat rads, whats the point when you have a heat pump plus a backup? Of course you can still go for a stove without back boiler as a room heater if you realy want to chop wood.

galwaytt

liamdenn wrote: »

I am also concerned that if we go to passive standard a stove with backboiler would throw out too much heat into the room.

... a couple of things:

1. ...the above will happen in a house, even below passive standard
2. ...if you have a stove/boiler/rads/etc, then it's not actually passive you're really thinking about, is it, but rather just an efficient, highly airtight and insulated 'conventional' home (which is the most economical to build, btw..). Nothing wrong with that, but, like your MHRV concerns, don't get hung up over the 'passive' label.

liamdenn

Hiya Galwaytt,
My understanding is that passive standard is 15kw of heat per m2 per year which of course can include any of the methods mentioned above. I guess why i keep referring to passive standard is that it a very clear understood standard. I do however feel that certain trade offs are made and for me at this point I feel that the best option might be to insulate to u values at passive standards( or near enough!) along with air tightness levels. and then ventilate with DCV ( a glorified hole in the wall I know). You need air and i think i can live with having to heat the controled amount of cold fresh air needed for the house. This is very doable if the fuel is free.
I am a bit concerned about the air to air heat pump comments. I understood that if you pick the "wrong one" it can freeze up etc but had never heard of the other issues. anyone else have any experience of it?
Cheers
Liam

quentingargan

Like other posters here I think your emphasis on reducing energy demand is right, and if you get this bit right, then the problem is that the return on investment for your heating system diminishes.

We also have access to free firewood, and in about 3 days work per year, we can saw enough timber for a year's supply for about 2 gallons of chainsaw petrol ( - and usually a couple of chains!).

We use an old-fashioned range to heat our 1,600 sq ft, and it works well enough for us, but we are happy to have bedrooms cooler than most. We often wonder about putting in a proper log gassifying stove, and may well do this sometime to boost heat, but not because it will cut our sawing time from three days to two!

We also have an over-kill on the solar side - 80 tubes - to maximise the season. I hate the idea of lighting the fire just for hot water. We usually get enough hot water from early March to October, plus some days for the rest of the year - happily the ones when we don't need the heating on. If you are thinking of doing this, be sure to use a heat dump of some sort.

liamdenn

Hi Quentin
I would be in the same camp about cooler bedrooms, in fact i prefer having the whole house a few degrees cooler than "the norm"

Out Of Order

liamdenn wrote: »

Hi All
Just want to run this by you all and see what you think.
I have been mulling over the pros and cons of a passive house for our own situation.
The considerations for us are as follows:
1.We want a well insulated home with low running costs
2.We want to be as self suffient as possible and not be relient on oil prices etc. I want to take advantage of a free source of wood to heat the house.
3. We want a low tech solution
4. We want a "traditional" looking house.A simple rectangle and not open plan. So a big kitchen, and then a sitting room and playroom. 4 bedrooms upstairs. Footprint of not more than 1900 square feet.

Well Liam,
This sounds something like what I started out with three years ago. After a lot of modifications, I was happy with the attached plans (there is also a verandah on the south side to prevent summer overheating which is not shown). No playroom as such, sure throw em in under the stairs!

Then after more deliberation I decided to build with block on flat and external wall insulation. My foundation detail is on another thread and I'm still trying to decide on the roof build-up.

For heating, I plan on just having a room-sealed stove with a back boiler.
Also solar for sumer DHW. HRV if I can afford it when the time comes, otherwise just trickle vents in the windows for the time being.

Hope this gives you some ideas.

liamdenn

Thats brilliant. when u reckon you will be finished

Out Of Order

liamdenn wrote: »

Thats brilliant. when u reckon you will be finished

Hard to say. I'm finishing the gables tomorrow and starting the roof next week. I'm going hard at it until it's weathertight so there's the roof, windows, and EWI to sort out and I'll tip away after that, doing it in stages. I'm only completing the ground floor for the near future anyway, so I will probably only insulate at joist level for now and stud accross where the stairs is located. I'm trying to keep the mortgage to a minimum so I'll tackle the airtightness and insulation at rafter level as well as the HRV in my own time. Hopefully I'll be moving in early next year though.

Ed12

Is it essential to have underfloor heating if using an air to water system?

muffler

Ed12 wrote: »

Is it essential to have underfloor heating if using an air to water system?

Please dont grave dig threads that are almost 2 years old.

Thread locked.