Jump to content

Heating, what if not a wood burner?


JohnRoss
 Share

Recommended Posts

[quote user="Théière"]

[quote user="Quillan"]Now not having a go at anyone but it seems this 1:1 might not possibly be correct, I draw your, and anyone else's attention, to page 51 that shows on average at -10, as that was a figure mentioned, that the COP figure could be between 1.8 to 2.0 and a little lower for -12. If I have misinterpreted the numbers please don't have a go just try and explain my error in simple terms.[/quote]

Q, it was more a sense of getting the concept across that with colder outside air the COP will fall dramatically from 3:1 or better.  The actual COP depends on many things not least the design and it's ability to cope with colder weather.  Even the best units will drop to a COP of 1:1 when it's cold enough and the heat needs increasing. The further apart those numbers are the less COP you receive.  It's ok in a lab to simulate but that's not real world and in a cold limestone house you may well need to set the heat warmer than their stated 21 deg and with temperatures dropping to around -17 round our way the other year I would much rather over spec and have heat in reserve than under spec and be cold even if it is only for 2 weeks a year.

[/quote]

So when I looked in to this a few years ago I was very sceptical about this COP number and more importantly the claims on saving money which is my main driving force. As far as I was aware you can't get something for nothing and going back many (many) years to school physics power in equals power out and that whilst you might get to 95/98% efficient you couldn't effectively get more power (in this case heat) out of the power you put in let alone three or more times the power.

It seems to me from what I have read that the 'secret' in all this is the gas and actual pump used. From what I have read, and this link I gave seems to confirm this, there are only a handful of pump manufacturers with names like Toshiba and Mitsubishi being the main movers. Now my cheaper units from BricoDepot actually have Toshiba pumps in them so it's nice to know they are not 'Oki Coki' but an actual brand. Gas, well with slight variances that seems to be much the same these days due to environmental controls.

Anyway being rather sceptical I decided to buy just one and run it for a year and see how it went and I have to say I was very surprised especially as that year we had temperatures down to -17 on more than one day. The heat is relatively instant, they take about five to ten minutes to start throwing out real heat and in the living areas we have them set to 23 deg in winter. Now I have no idea how you can measure the COP rating in a normal household environment but what I do know is that either the old, very expensive, electric radiators were absolute cr*p which at 600 Euros a pop back in 1998 I doubt or these things really are as good as they say they are and to my mind the size of the reduction in my electricity bill seems to confirm that. Even in a case like yours with thick walls (I am not trying to sell them to you by the way) the potential saving would pay outright for two electronic paraffin heaters and enough paraffin to run them for two weeks and after the second year still save money, you could even install another wood burner.

I read a bit of that report last night in a bit more depth and I did find it interesting that smaller is better i.e. don't buy massive outside units and try and get 5kw out inside but go for the 2.5 to 2.8kw units or bi split units (one bit outside and two bits inside) as smaller units are more efficient. The also tested cheap Chinese imports (well they actually say Asian) and found that whilst they were not as good as branded but because they used some branded components like Toshiba etc pumps there was only a small difference in performance. Also don't forget that these results are a combination of individual tests carried out by many people in many EU countries.

Link to comment
Share on other sites

Well you folks have given me a lot to think about so thanks for that. Here is what I am thinking now. We don't keep the Supra in as it were during the night but it does go on producing heating during the night due to the two large stone panels on the sides. That could be done, somewhat better I suspect, by a nightstore/accumulateur of say 2kW. I suspect a static version might do. We aim to keep our downstairs area between 21 and 22 degrees C in the daytime with the Supra except for the first part of the day when additional heat sources like electric panels or paraffin heaters might be needed for an hour or so. By the morning on trotting downstairs one might expect to find room temperature to have fallen to 17 or 18 degrees and not lower than 16 degrees in a normal winter here in Deux Sevres. We don' heat upstairs and the bedroom would typically be not lower than 14 and usually about 16 upon retiring for the night which is fine once one is in one's pit. Temperatures outside frequently go down to -2 or -3 degrees Celsius and once in a long while as low as -10 C in Winter. Only once been as low as -18 C in the last 12 years.

So with this all in mind it seems to me that an air to air heat pump would need to be able to raise our 60 square metres downstairs area and to hold it at between 21 and 22 degrees Celsius as the Supra does at the moment during the day. This raises the question what power input would this heat pump need to do that. It would not run at night and normally one could expect outside temperatures to be above zero in the daytime for the majority of time during the winter. I take note that smaller power input devices might be more efficient that one big one. I could fit two if one would work on a NW facing wall and the other on a SW facing wall but I would prefer no more than a total of a 2kW loading. Need some reserve for cooking, water heating and a 1kW fan heater from time to time. The Nightstore would also be producing heat during the day which would reduce the power output needed from the heat pump.........................JR 

PS If I do buy a Zoe as a second car for local trips with its 3kW charger I might have a supply problem!

 

Link to comment
Share on other sites

Well here is two pennies worth.

Wood, we keep three years worth. We have wood outside in two piles, one two years old and the other three. The three year wood currently stored outside under cover will be moved to the garage in about September as it spends most of the summer facing the sun and so dries out. That will be replaced with new wood from the yard which has normally also been out for a year drying anyway but then its not vcovered in the yard. The wood from the garage is what we use over the winter so it is nice and dry. Being that the garage is under our house it won't even get wet in transit to the fire and of course even in winter the garage temperature is around +12.

Choosing your air source heat pump. Most sites give the square meterage of the room it will heat for example a 3.5kw unit will, with a normal ceiling height heat 40m2 so I would go for two which gives a little extra capacity. I am not a fan of bi-split units because the ones I have seen use the same gas circuit and there is only one pump so if you have a leak or the pump fails you loose all heating where as with two singles you still have one working. Two single units are often around the same price as a bi-split unit.

Price wise you need to add a further €150 to the price for the mounts and pre gassed pipes which are 4M long. This means you can install them yourself and once you have done one the rest are easy. It took me around six hours to fit the first one after which it took just a couple of hours. These units are powered from a normal mains socket on the inside of the house and you get a cable with a moulded plug on the end attached to the 'inside' unit, the length of cable is between 1M and 1.5M depending on make. You need to take that in to account when working out where to place them. Our outside units are on walls that don't get direct sunlight except of one which I built a wooden box round with a mesh front because air circulation is very important. This also effects where you can place them because the pre gased ppes are only 4M long. I fitted the inside unit first with pipes attached then ran the pipes outside and finally mounted the outside unit.

Leroy Merlin Single type 3.5kw unit. (€579)

http://www.leroymerlin.fr/v3/p/produits/pompe-a-chaleur-air-air-pack-monosplit-alpina-4103-3500w-e60410

BricoDepot Single type 3.5kw unit. (€569)

http://www.bricodepot.fr/carcassonne/climatiseur-reversible-dc-inverter-pour-une-piece-jusqua-40-m-%28105-m3%29-/prod29158/

Typical extras you need (important - the ones below are for BricoDepot units, you should buy the equivalent of these pieces from the same place as you buy your units, these are just to give you an idea of cost).

Pre gassed pipes (a pair) €115.00

http://www.bricodepot.fr/carcassonne/search/node/820221?query=820221&pageSize=20&categoryId=navCatalogRootCategory

Pipe clips 9per bag of 10 €4.15

http://www.bricodepot.fr/carcassonne/search/node/810334?query=810334&pageSize=20&categoryId=navCatalogRootCategory

Outside unit mount €26.90

http://www.bricodepot.fr/carcassonne/search/node/820247?query=820247&pageSize=20&categoryId=navCatalogRootCategory

You will also need a 'core bit' to drill through the wall. I think mine was 40mm but check the instructions for fitting the units, the size will be there. You will also need some "squirty" expanding foam to fill the 40mm hole once the system is installed and you know it works.

Mine came with a DVD showing you how to install it which was very good, you don't need to understand French to work it out.

Personally for the pipes I put them in large plastic trunking outside and put that clip on water pipe insulation round them first then stuffed some old rockwool insulation in as well before putting the lid on. Looks smarter and means your not loosing heat through the pipes.

Hope that helps.

Link to comment
Share on other sites

[quote user="powerdesal"]Whilst totally irrelevant to the main thrust of this thread, this may be of passing interest :- Delivered price ( to France) of a Rayburn 355SFW from the North of England = Euro 5500 Delivered price from a French Rayburn dealer = Euro 7000.[/quote]

Why?

Link to comment
Share on other sites

Two reasons:-

The contrast in prices of heating appliances may be relevant to someone who 'may' want to investigate HP prices in UK vs HP prices in France.

I thought the contrast in prices may be of general interest but couldn't be bothered to start a new thread.
Link to comment
Share on other sites

Q, with such long posts I'll start here to continue:

I like heat pumps and I have done two courses from different manufacturers, It is longevity you gain from branded pumps. The ability to cope with a wide range of temperatures comes from the auto defrost cycles (lowers the COP)  and the various  evaporator /heat exchanger and gas types for performance.

Radiators by comparison don't radiate at all well neither do they convect that well unless you have a draught and who wants one of those. Forced air convection as you have noticed from your air source works far better which is why I am currently designing a forced convection fan for radiators as I have a prototype which works brilliantly.

John Ross, I you had a fan above the wood burner it would circulate and warm most of your space far better than you can currently believe. I am making a register plate with vents for a customer as too much heat is currently ducted upstairs to the bedroom compared to how much is needed downstairs in the lounge.

Link to comment
Share on other sites

[quote user="Théière"]

John Ross, I you had a fan above the wood burner it would circulate and warm most of your space far better than you can currently believe. I am making a register plate with vents for a customer as too much heat is currently ducted upstairs to the bedroom compared to how much is needed downstairs in the lounge.

[/quote]

That is a most excellent point. We have a large office type fan on top of a unit next to the fire. We only turn it on to the lowest speed but it helps 'push' the captured heat from the vaulted ceiling back down in the room and stir it up a little. I know from painting the ceiling that the temp at floor level without the fan can be 20 deg whilst up on the ladder it can be 30 or more degrees.

Link to comment
Share on other sites

The Supra Orlando Olliare, the model we have, has a turbo fan fitted as standard and which blows air underneath the fire box and creates a warm draft so yes a fan helps indeed. It is either operated by a built in thermostat or manually with an on off switch.......JR
Link to comment
Share on other sites

I would be interested to know too. We have a well which is not used for owt as whilst the chemical analysis was good the water was full of nasty bacteria. What depth of water would be needed ours, as you might expect, is low in summer and a lot higher in Winter. Quite close to the house so long pipes would not be needed......................JR

 

Link to comment
Share on other sites

[quote user="JohnRoss"]

I would be interested to know too. We have a well which is not used for owt as whilst the chemical analysis was good the water was full of nasty bacteria. What depth of water would be needed ours, as you might expect, is low in summer and a lot higher in Winter. Quite close to the house so long pipes would not be needed......................JR

 

[/quote]

You obviously didn't read my earlier post. My thoughts are that the system is too expensive, not as cheap to run as they make out, and needs real expert knowledgeable people to keep on top of it, and there ain't too many of those about, (don't take any notice of the signs  they have on the sides of their vans)  Following on from my experience of the system I wouldn't entertain it at all.

                              By the way you would need a pump house etc. for the well, then of course the system itself. My neighbours came in around 20.000Euro and he already had the pump and pump house for the well. In my opinion unless you are very young and very rich you will never get your money back. As my neighbour is in hospital at the moment we have just paid her electricity bill, much more than our Oil/Wood/electric combined. (What can't speak can't lie). Good luck

Link to comment
Share on other sites

Thanks for the reply Nick,

I'm currently revising my heating from tired Electric rads in the bedrooms to air to air exchanger in the bedrooms (for the dual air con feature) and since I'm tired of making up / cleaning up after the wood fire my friendly plumber is convincing me to install underfloor heating (70sqm) from air to water Heat Pump, Any experience of this out there?

 

 

Link to comment
Share on other sites

  • 2 weeks later...

Saw the price and an expletive burst from my lips.

Get an office fan, they don't burn much electricity and just run it on the slowest speed. We have ours on top of a cupboard and it does the job very well. Seem to remember it cost less than 30 Euros.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...