Air Source Heat Pumps

KernowMan_2

Hi, I am new to this forum but have read much of the information with interest. In the original post and in subsequent posts I feel that Samtheman 1K has offered useful information regarding his installation. I would like to ask a few questions of Samtheman if he still comes online and also invite the views from others regarding the dilemma I have regarding our heating system.
At present we have an oil fired Rayburn Range cooker (which we do not use for cooking) which was in our 3 bed bungalow when we moved in. We have ten radiators and the Rayburn it seems has never been quite up to the job of heating the property and providing domestic hot water. Now the dilemma. On inspection I notice that our oil storage tank has cracked and will need replacing if we stay with oil heating. The cost of replacing the tank would be just shy of £1,000. Given the inefficiency of the present system we are considering putting the £1K towards either a wood pellet (Rika Evo Aqua) boiler to replace Rayburn or an ASHP possibly combined with a solar collector. Could I ask Samtheman if you considered installing a solar collector as well as your ASHP and invite any thoughts anyone else has on doing this. It seems that the Gledhill Torrent HP in conjunction with the Mitsubishi Ecodan would be an ideal combination along with a solar collector.
I understand from what I have read that I will have to re-size (replace) our radiators but in reality will an ASHP alone or in combination with a solar collector provide adequate heat for our room heating and domestic hot water? We live in Cornwall so reasonably mild winters.
Thanks in advance.

Cardew

Whilst ASHP's clearly have merit, a solar collector is a joke in money saving terms.

You will be lucky if you get 1,000kWh pa out of a solar system. Assuming your ASHP gives you a CP of 3 that 1,000kWh will be worth £30 to £40 pa and cost ???? to instal.

samtheman1k

Hi,

yes, you will have to resize your radiators, or just add some more, or add some underfloor heating. You will have to add a thermal store (perhaps the Torrent, as you've already mentioned) and the ASHP. This is going to add considerable cost, far more than the £1000 you mention (think £5k min just for purchasing items, let alone installation costs). In your situation, it is hard to justify an ASHP due to the high installation costs, and relatively low cost of oil at the moment.

As Cardew says, solar collectors rarely pay back their installation costs, and can't really be used for heating as far as I know.

Conceptually though, yes an ASHP can do what you are asking (have you room for a GSHP though, as they'll run cheaper). Work out the KWs required for your house, then use that to size the ASHP you require, add on the thermal store and extra radiator costs, and that should be your price!

paceinternet

I would like to add to the wise words already posted that the capital cost of an ASHP installation may become too expensive if you go with a heat store and high profile brand name. If it does, do reconsider alternative suppliers.
I have written a few times now about sizing a heat pump to obtain a cost effective solution rather than 1 device providing for the lowest temperature conditions. Try a search if you want more info. But, all heat pumps, and particularly air source, have reduced outputs at lower ambient temperatures.
The balanced solution is to have an additional heat source available for the few days when the ASHP output is below the total heating that is needed.
Do not accept any supplier just telling you their system is rated at 12kw when it can only deliver this at 7 degC air temperature. Ask what it will be at 0, -5 and -10. Then you can decide if a bigger ASHP is worth considering, or add into the system an additional heat source for however many days your weather needs it.

In many cases, the heat store doesn't store any worthwhile amount of heat, but only blends different temperatures from the sources. Then the additional controls make the system ever more complex requiring more costly maintenance.
I believe, and soon hope to demonstrate, that a KIS solution is better than a heat store and lots of controls. Using an ASHP at maybe £2k plus an electric boiler (or maybe another fuel) in series for those additional amounts of heat.

richardc1983

Oversize if possible as the extra capacity will be a bonus when very cold!

Cardew

KernowMan wrote: »

Hi, I am new to this forum but have read much of the information with interest. In the original post and in subsequent posts I feel that Samtheman 1K has offered useful information regarding his installation. I would like to ask a few questions of Samtheman if he still comes online and also invite the views from others regarding the dilemma I have regarding our heating system.
At present we have an oil fired Rayburn Range cooker (which we do not use for cooking) which was in our 3 bed bungalow when we moved in. We have ten radiators and the Rayburn it seems has never been quite up to the job of heating the property and providing domestic hot water. Now the dilemma. On inspection I notice that our oil storage tank has cracked and will need replacing if we stay with oil heating. The cost of replacing the tank would be just shy of £1,000. Given the inefficiency of the present system we are considering putting the £1K towards either a wood pellet (Rika Evo Aqua) boiler to replace Rayburn or an ASHP possibly combined with a solar collector. Could I ask Samtheman if you considered installing a solar collector as well as your ASHP and invite any thoughts anyone else has on doing this. It seems that the Gledhill Torrent HP in conjunction with the Mitsubishi Ecodan would be an ideal combination along with a solar collector.
I understand from what I have read that I will have to re-size (replace) our radiators but in reality will an ASHP alone or in combination with a solar collector provide adequate heat for our room heating and domestic hot water? We live in Cornwall so reasonably mild winters.
Thanks in advance.

As samtheman states you are looking at very high capital costs if you are going down the Ecodan route.

As that system will entail new radiators, you may be better to consider a conventional Oil CH system with a combi boiler(I assume gas is not available).

You should be able to retain your radiators, no HW tank required, no boost of Hot water by electricity required, and much higher output from the boiler.

Oil running costs with a modern combi are probably lower than an ASHP.

samtheman1k

paceinternet wrote: »

In many cases, the heat store doesn't store any worthwhile amount of heat, but only blends different temperatures from the sources. Then the additional controls make the system ever more complex requiring more costly maintenance.
I believe, and soon hope to demonstrate, that a KIS solution is better than a heat store and lots of controls. Using an ASHP at maybe £2k plus an electric boiler (or maybe another fuel) in series for those additional amounts of heat.

The thermal store stores hot water for cooking, bathing etc, not for heating the house. It is basically just an immersion heater with a direct heating coil from the heat pump. It is a must if you want instant hot water!

paceinternet

Thermal Store, Buffer Tank, Hot Water cylinder, Accumulator Tank, Thermostatic Tank, Heat Bank.
You will find the terms used in different ways, but generally a Thermal Store is an indirect hot water tank in reverse. The heated water from ASHP etc is in the tank, and the water going out to taps and radiators is in separate coils in the tank. Lots of variations
See:
http://www.heatweb.com
And:
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1215

As samtheman1k says, http://www.gasapplianceguide.co.uk/thermal_store.htm

Another supplier descibes the following -Suitable heat pump connection into the heating system is through a so called buffer tank providing double function:

- separation of the flow through the heat pump and the flow through the heating system which ensures a stable flow through the heat pump and thus heating water constant warming too.
- the buffer tank contains a heating water quantity sufficient for heat pump defrosting by means of cooling circuit reversation (as considered for the event when the heating system does not have such sufficient quantity of water that is necessary for defrosting by reversation of the heat pump function).
- the buffer tank contains a heating water quantity sufficient for prevention of heat pump cycling in adverse conditions depending on the heat requirement of the building.

jules2

Hi peoples, new to this, found forum while researching air source heat pumps. Advise please: I’m a cold mortal, live in a 30 yr old detached bungalow with large garden in Devon, concrete floor throughout, currently with economy 7 storage heaters in most rooms. Living area at rear of bungalow faces north east, so cool in summer, freezing in winter. Ground source pump and underfloor heating just too much work. Oil too expensive. Could install wood burner with back boiler, but not keen on extra work/mess cleaning fire grates, wood storage etc. Mains gas not available in our little town. Drawn towards air source heat pump – greener, cheaper to run etc but need the flexibility of a gas-fired central heating system. Plumber brother can get radiators etc at cost and install, he’s put ashp in new builds with underfloor heating but not with rads. I need background heating, with instant heating if very cold and hot water for kitchen and shower (had bath taken out as never used it) and not sure ashp can provide this. Advise gratefully received asap, had hoped to get things sorted before this winter, ha ha! Many thanks.

Cardew

jules2 wrote: »

Hi peoples, new to this, found forum while researching air source heat pumps. Advise please: I’m a cold mortal, live in a 30 yr old detached bungalow with large garden in Devon, concrete floor throughout, currently with economy 7 storage heaters in most rooms. Living area at rear of bungalow faces north east, so cool in summer, freezing in winter. Ground source pump and underfloor heating just too much work. Oil too expensive. Could install wood burner with back boiler, but not keen on extra work/mess cleaning fire grates, wood storage etc. Mains gas not available in our little town. Drawn towards air source heat pump – greener, cheaper to run etc but need the flexibility of a gas-fired central heating system. Plumber brother can get radiators etc at cost and install, he’s put ashp in new builds with underfloor heating but not with rads. I need background heating, with instant heating if very cold and hot water for kitchen and shower (had bath taken out as never used it) and not sure ashp can provide this. Advise gratefully received asap, had hoped to get things sorted before this winter, ha ha! Many thanks.

Welcome to the forum.

I don't know that ASHPs are greener other than they use less electricity.

The downside of ASHPs are that they don't have a huge output so won't give you the instant heating you require. The water does not get that hot in radiators and they are well suited to underfloor heating. If you need Instant heat in one room you can always use a 'normal' heater to boost until the ASHP has brought it up to temperature.

Most ASHP systems do not provide very hot water for showers and you need to boost occasionally with an immersion heater.

An ASHP is still a lot better than storage heating IMO, however like most things in life - it is a compromise.