New build - heat, ventilation and hot water

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.

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?

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.