'' I will be insulating the floors and external walls with 6" celotex or equivalent ''.

Internally or externally? If internal, notwithstanding that you'll get a very satisfactory U value, be very very very careful about the interstitial condensation risk. Your ext walls will be very cold and dependent on the perfomance of the vapour Control Layer (VCL). Can you do solar water heating too?

For sure you should insulate first, I would rather see external wall insulation, then assess the heat loss then design the heating system if needed.

It pains me to raise this but you could consider wood pellets, GSHP is a good option though.

With 6" of cellotex I cant see you needing much of a heating system and so please do the calcs first, an ashp might do it costing less than a grand.

SSHP (sea-source heat pump)? There's one in use on the south coast of Ireland, IIRC.

Thanks Beau- is the weather compenstion device worth having? Does it make the system more efficient?

Is your HP an inverter model? I have been advised to have a 5-11kw variable output inverter heat pump. The idea I beleive is that it runs more or less constantly and varies its output depending on the temperatures required as opposed to fixed output HPs which vary their output by switching on and off all the time. Do you know much about this?
Bob

Posted By: rangichangisamSSHP...there is no way I would get permission to build the filter stations or whatever...

Ok, probably not practical in your case but worth mentioning. For the record, though, the usual scheme is to just put a loop of pipe in the pond/lake/river/sea and run the HP input fluid through that, rather than take external water into the HP. Therefore no filters. Apart from avoiding jelly fish, etc, in the HP it also allows the use of antifreeze; remember that the output of the heat pump will be cooler than the source water.

Thanks all,

Steamy Tea- I am on the Gower Peninsular, South Wales. Heat Loss has been calculated as a whole I beleive (the company installing the sytem calculated it. What would be the implications of doing calcs room by room?

Sprocket- The power level is 5-11kw and I'm having a vertical 140m borehole

Keep the ideas coming!
Bob

5-11kw is really quite modest/decent for a 4 bed house. Was that assuming your proposed 6" PUR foam insulation and air tightness? ie. did they take the current spec PLUS assumptions about your improvements as the target they were intending to heat? Not necessarily a sign of evil intent but of course it gives your GSHP spec/installer a way-out if they underdeliver (can blame your improvements as under spec). Just something to think about. You may want to get fairly sure of what you can do for air-tightness and insulation.

Since you say you will insulate the floors, does this mean you will be putting in new UFH and screed? If so then I would suggest you budget for UFH pipes on 100mm centres (ie. very dense pipes). It will let you run the GSHP flow temp lower so you get better efficiency. Cost will go up a bit because more pipe needed but don't let anyone tell you you can get away with less IMHO.

The standard installer GSHP system would include a fair sized buffer tank (separate from your DHW water tank) and zoned heating. Is that what you are looking at? Do you have space for that extra tank? It is possible to do away with the buffer but it needs careful thinking about (and preferably elimination of) the heating zones. Fairly easy on a new small-ish eco-build but practical issues or perceived risk means most installers insist on the buffer tank. However the setup is much simpler without the buffer and zones if (and only if) your building's outer envelope is up to it (ie. just heat the whole house all the time).

If you are considering a secondary heat source (ie. in addition to the GSHP) then the buffer tank is a no-brainer so that consideration goes away.

Regarding the borehole, can you get a fixed price for the drilling? Unexpected geology (like we found lots of here) can risk pushing the price up considerably so good to eliminate that risk if you can.

Drilling is not cheap. I would expect a 150m borehole to be a significant proportion of the install costs.

Regarding the GSHP, can I ask what manufacturer/model you were recommended? Did you get a choice?
Most GSHP contain supplementary electrical heaters. It is common practice to specify a GSHP to provide a proportion (i.e.. less than 100%) of the expected peak thermal load and let the electrical heaters pick up the shortfall on the coldest days. If the heat pump itself is adequately sized then the electrical heaters will rarely (if ever) kick in. But if undersized you can end up running some significant proportion of your winter load on electrical heating (ie. very bad). Again, not necessarily a sign of evil intent but you should be aware of it.

If you achieve reasonable air tightness you will need to be thinking about ventilation too.

<blockquote><cite>Posted By: rangichangisam</cite>Thanks Beau- is the weather compenstion device worth having? Does it make the system more efficient?

Is your HP an inverter model? I have been advised to have a 5-11kw variable output inverter heat pump. The idea I beleive is that it runs more or less constantly and varies its output depending on the temperatures required as opposed to fixed output HPs which vary their output by switching on and off all the time. Do you know much about this?
Bob</blockquote>

Weather compensation was the recommended way for an efficient system when we were shopping around (about 6-7 years ago). Does it make it more efficient? In all honesty I don't know but it does keep the house at a steady temperature once you get it set up right. I think it does allow you to use a small unit as it does not get caught out with sudden changes in internal temperature but I am no expert at this.
The way it works on our GSHP is the system is managed off the outside temperature and not the inside. You have what is termed a heat curve which you will need to adjust to your house. This is how much the heat pump has to react to the changes in external temperature. For example if your house is badly insulated and the temperature outside starts dropping you will need a high curve which means the heat pump will have to raise the heating circuit temperature dramatically to keep your house at a steady temperature. Inversely if your house is well insulated you will need a low curve so now when the outside temperature starts dropping the heating circuit temperature will not need to raise much to keep the house at steady temperature. To adjust how warm you want your house you can just turn the balanced curve up or down. I do not know if a heat curve is an industry standard measure or if specific to each manufacturer but our controller is a Rego 637 and our heat curve is 1.6. I was told by our GSHP suppliers this was very good but then they would say wouldn't they

I hope that made sense

Our GSHP is of the fixed output variety and I am afraid I know nothing about the variable output type.

Thanks all for your comments- I feel like I am probably making quite a sensible move after all. Splashing out vaste amounts of money on heating systems does funny things to your nerves !

Posted By: mike7sea and thus more temperate than average even for the UK

Has more heat, which is just another word for energy, at a higher mean temperature. I knew what you meant
May be a problem with mist, not seen any evidence, just guessing. Does anyone know anything about icing of ASHPs?

> as I understand it buffer tanks are there too fill the lag in between the call for heat,
> the Hp turning on and the delivering heat

A HP will atually deliver heat within seconds of being turned on. Up to full power within the first minute too. The main reason for a buffer tank is to be able to deliver small amounts of heat. A normal heat pump likes to deliver full power and it does not like to be turned on and off at short intervals. Aside from wear to the heat pump parts the start current for the big 3-phase motor is not something you really want happening a lot either. Zoned heating can require a heat pump if the zones are small or may all go off. Driving radiators or fan coils rather than UFH may also require a buffer because of the very low load as air approaches temperature.

If you genuinely can keep the heat pump running even at low loads then no buffer should be needed. I guess that's the 5-11kw range you mentioned? I wonder if 5kW will be low enough.

I'm not familiar with inverter heat pumps. I'm interested to know more about it though. I assume the "inverter" part is a voltage converter to drive the main compressor motor at variable speeds. Motor driving tech has come a long way because of recent development for electric vehicles etc (higher voltages, latest high power low loss semiconductors, neodymium permanent magnet motors, fancy micros to control it etc). I'll Google it for more info of course but does anyone here have any direct experience with these heat pumps vs the regular type?

Posted By: Sprocket5-11kw is really quite modest/decent for a 4 bed house.

Depends if that's input or output. As output is sounds a bit mean. If you're planning to insulate and increase airtightness then the GSHP people need to know the house as it will be rather than as it is now to spec an appropriate size system.

ASHP do ice up which is why they don't work as well in our damp cold weather as in colder but drier countries. Most have a de-icing system which obviously reduces efficiency. That said we are very happy with ours but if it seriously misty/foggy a lot of the time the GSHP may be better.

Hi,
Mike 7- I am at the bottom of a fairly cold valley so whilst I am right by the sea I am also affected by the valley. The cold air tends to sink to the bottom of the valley and hang around way after the air at the top of the valley has warmed up. We also get quite a lot of sea mist.

Nick- thanks for your advice, I'll google the breaking the mould stuff and try and get my head around it. I do have stone walls with rubble infill so your points re air tightness were very relevant, thank you very much.

Bob

Hi, yeah I'd calculated the U-value at about that too. Anyone got any tips on minimising thermal bridging when fixing celotex to external walls? My plan was to use spray adhesive and then fix the plasterboard to the wall through the insulation with a few plastic insulation fixings like these:

http://www.ebay.co.uk/itm/Kingspan-Marmox-Insulation-Anchor-Cob-Plug-Fixing-Dowels-60-90-or-110mm-/150803504677?pt=UK_DIY_Material_Nails_Fixing_MJ&var=&hash=item231c96de25

As I will be lime plastering the heads will be covered by a thick layer of plaster anyway.

Maybe i should start a new thread on this? Thoughts welcomed anyway
Bob

Bob,

What's the state of the walls now? Are they plastered (and if so, ? with old lime plaster?) or are they stripped off? If they are stripped off, then I am afraid you need to do a parging coat (rough air-tightness layer) of lime render to air-seal (but not vapour seal) the walls before you insulate. get that trowel out!

Nick