heat pump or not

Shanaknocker

hi,
I am planning on building a new house, split level witch will be to Passive standards, ie U-values of 0.15 in most areas and triple glazed windows. I did not go down the route of Certification so do not have the PHPP done on the house. My intention is to get my house down to below 30kwm2. My issue is every company we talk to wants us to buy Heat pump with underfloor heating or a large KW heat pump costing a large amount.
My first intention was to go down PV route, but PV panels not up to scratch yet. I am looking at a thermodynamic panel, which will give me 365 days of hot water and to use this hot water to heat a post water grill that is attached to my MHRV, does any know will the Thermodynamic panel be enough or will i have to go down the heat pump route. House is roughly 210m2

murphaph

Whatever you decide as your heat source (IMO probably the least critical decision you'll make after your levels of insulation and airtightness and your heat distribution system) you should ensure that the UFH is laid out in a manner that will enable you at a later date to run it from a low flow temperature device like a heat pump, should you so decide.

If you install UFH with too wide spacing between pipe runs, you will never be able to run it off such a device except by jacking up the flow temp to a point where the device is operating completely inefficiently (this also applies to modern condensing boilers too I guess).

You are also entirely correct to be worried about an over sized heat pump. An over sized heat pump is a disaster as it will cycle on and off far more than a correctly or slightly too small HP (slightly too small is fine if you have say a little stove to make up the difference on the coldest days). heat pump cycling is bad news because the compressor is only good fo x thousand cycles but more importantly perhaps is that the compressor is run by a motor. Motors consume the most energy when starting up. They are efficient once they are spinning. You will use much more electricity starting up the heat pump many times than just running the smaller one all the time.

Here in Germany (and also in the UK and most? other EU countries) it is standard practice to perform a heat demand calculation according to EN 12831 at the design stage, where the U-values of all your building materials as well as surface areas and typical outside air temps flow into a series of equations to fairly closely estimate the heat demand of each room (important for correctly determining UFH loop size, gap etc.) and then a sum total of all the heat demands gives a value for the size of the heat source. These things aren't perfect-I found errors in my own one done for our low energy new build here and had them redo it, but even the calculation with the error was still far more accurate than just guessing.

This is not commonly performed in Ireland for some reason.

http://catalogue.segen.co.uk/reseller/docs/EN12831.pdf

Shanaknocker

thanks Murphaph.

My DEAP report hopefully will give me a good indication to what heat load i will need. I was quoted for a 11kw system, again i think this is to big and will, as you said will cycle on and off. Im looking at a 6kw system, without UFH, possibly a few low temperature rads in the wet rooms, as this extracted heated air will heat the air coming in.
The lack of information out there in relation to the post water grill heater is my stumbling block. My delema:
A thermodynamic panel cost 2/3 of the price of a Heat pump.
thermodynamic panel has no/little maintenance where as HP has issues with breaking down and warranty.
House wont need a lot to heat, I am been very exact on insulation and air tightness,
I want a system that wont use alot of KW in operation. (had previously looked at PV panels, electric immersion, a electric MHRV post heater and electric rads) PV panels were coming in a little more expensive than HP, but it was an investment.

Hard to get advice from an independent source

murphaph

You might also consider a more traditional high efficiency gas boiler with solar thermal. If your energy requirements will be so low, there is an argument to be made that you can install "any" heating source as it won't actually be in operation all that much.

I suppose there is no right or wrong answer. Heat pumps are common as muck over here, so installers and warranty are not really big considerations but in Ireland I read a lot about warranty issues and poor installer service/lack of knowledge. For these reasons I would also be wary of heat pumps in Ireland (and I think air source heat pumps are simply not that well suited to the temperate climate in Ireland because it so often hovers around freezing in winter, you will get a lot of defrost cycles compared to a colder continental climate (drier, colder air causes less ice buildup).

dhaslam

Heat pumps and underfloor heating work well in well insulated houses, floors can be a few degrees warmer than the required room temperature. Rooms that don't have passive heat need a heat source even if well insulated. Also of course in dull winter weather heat will be required in most rooms. I have a 3 kW heat pump which usually runs during reduced rate hours only so the annual running cost is about €200. During the day heat is supplied from a buffer tank. Living room is normally set for 22C during the day and 23C in the evening. Wall cavities were limited to 150mm due to outdated building regulations in Ireland but otherwise the house is fairly well insulated.

The big problem in Ireland is the lack of reasonably priced sources for both equipment and installation. This means having to import equipment and do a self install. A small heat pump makes it easier to send abroad for repair if necessary. The ground loop should cost hundreds rather than thousands and is best installed when building so that pipes enter the house underground. The heat pump cost itself is still a bit of a stumbling block but perhaps not too bad when compared with the cost of alternatives that may need chimneys or storage facilities or both.

I am interested in heat pumps, I have one in the Nissan Leaf EV and it is extremely efficient but notably less below 0 deg C but still far better than a fully resistance heating system, for an Irish climate it's brilliant.

We are moving house in a few months and would like eventually to install an air to water heat pump which I think would actually work well in Ireland and they're getting more efficient all the time.

Also , Ireland is suited to Solar PV contrary what people may think, there is a huge amount of Solar PV applications waiting to be approved in Ireland for commercial Solar PV, I think up to 3-4 GWp which is about the same as our wind energy installed capacity which can alone power 50% of our total peak supply on a windy day which is pretty amazing but we also need Solar PV the problem is there is no Government support and there is no support for domestic installations nor any form of Feed-In-Tariff.

There are rumours this will change in 2017.

Anyway the point I'm making is that if there is support for solar PV it would make an ideal companion for heat pumps and you don't even have to worry too much about air tightness etc , if there were a feed in tariff then all the excess you generate in the long Summer hours you buy back in winter to run the heating in Winter.