Air source heating pump
Discussion
we have recently moved into a new place which has an air source hearing pump...it’s an air to water system. It’s used for hot water and heating, we have underfloor heating downstairs and rads upstairs. The house is about 2000 sq ft.
The problem is that I am not sure we are using it right.
In our old house which was about 1500 sq ft we had a gas boiler, and underfloor...we paid about £70 a month for electricity and gas. We’ve been in the new place for 6 months so mostly in the summer months with no heating on, just hot water and it’s almost double the cost at £120 a month...I’ve got a fear on how expensive it’s going to be in the winter!
I’ve got it set up so the hot water comes on for about 3 hours split through the day. The heating is on for a couple of hours in the morning and a bit longer in the evening.
I thought these systems were supposed to be pretty cheap to run....am I doing something wrong?!
The problem is that I am not sure we are using it right.
In our old house which was about 1500 sq ft we had a gas boiler, and underfloor...we paid about £70 a month for electricity and gas. We’ve been in the new place for 6 months so mostly in the summer months with no heating on, just hot water and it’s almost double the cost at £120 a month...I’ve got a fear on how expensive it’s going to be in the winter!
I’ve got it set up so the hot water comes on for about 3 hours split through the day. The heating is on for a couple of hours in the morning and a bit longer in the evening.
I thought these systems were supposed to be pretty cheap to run....am I doing something wrong?!
mathmos said:
I’ve got it set up so the hot water comes on for about 3 hours split through the day. The heating is on for a couple of hours in the morning and a bit longer in the evening.
I thought these systems were supposed to be pretty cheap to run....am I doing something wrong?!
Yes. Heat pumps are woefully inefficient if you run them intermittently. I thought these systems were supposed to be pretty cheap to run....am I doing something wrong?!
They work best if they're running constantly: which means, as 280E says, that they are best suited to a very well insulated and highly airtight property and/or high levels of occupancy, otherwise you're paying for heat continually being lost if the house is poorly insulated and you're running the heat pump all day while you're out.
mathmos said:
Nope, no solar panels....just mains.
Does appear to be very expensive....started thinking about getting gas installed
I just thought that was part of the deal with them? Does appear to be very expensive....started thinking about getting gas installed
As others have said, without the cheap electric that some solar panels would bring to the party, they aren't much good in the UK.
mathmos said:
....started thinking about getting gas installed
Does the house already have mains gas available? How old is it?Has the ASHP been retro-fitted to replace an existing gas boiler, or was it part of the original build?
Apologies for all the questions, but a little more info is needed
Solar panels won't help you much in the winter when you need the ASHP.
They are used in much colder climates than here (e.g. popular Sweden I think).
If you are on mains gas then I'd change and use that, if not, insulate.
Heat pumps are great in high occupancy houses to maintain a constant temperature. We have a GSHP doing just that in a large old house. My monthly electricity DD is £170.
If you are on economy 7 heat water overnight.
They are used in much colder climates than here (e.g. popular Sweden I think).
If you are on mains gas then I'd change and use that, if not, insulate.
Heat pumps are great in high occupancy houses to maintain a constant temperature. We have a GSHP doing just that in a large old house. My monthly electricity DD is £170.
If you are on economy 7 heat water overnight.
280E said:
Which model of ASHP have you got? What flow temperature do the upstairs rads run at?
Unless your house is very, very well insulated, an air source heat pump may not be the best solution. Their efficiency also drops off at low air temperatures - just when you need it the most
Honestly not sure, I know it's a Mitsubishi,,,looking at the net it might be an Ecodan? I'll wonder out this morning and see if I an see anything that identifies the model. As for flow temps again no idea really...I can feel the underfloor heating on downstairs, but the upstairs rads seem to be cold all of the time, or at very best slightly warm to the touch. The house seems to warm up OK, although I suspect all of the heat is from underfloor rising through the house.Unless your house is very, very well insulated, an air source heat pump may not be the best solution. Their efficiency also drops off at low air temperatures - just when you need it the most
The house was built in 2009 so not that old and I think it's fairly well insulated....but no unfortunately they didn't bring gas up to the house when it was built...I am told it runs along the road which is maybe 10m from the front of the house...so I would guess we would need to pay for a trench and then connecting the house up, plus a boiler....I am guessing at anything between £5k-£10k to convert it. Looking at how much the ASHP is costing in running costs plus servicing I could be looking at 5 years to break even if I swapped.
mathmos said:
...it's a Mitsubishi,,,looking at the net it might be an Ecodan?
The house was built in 2009 so not that old and I think it's fairly well insulated....
I've done estates around that date, with heating systems based on the Mitsubishi Ecodan, built to Code for Sustainable Homes Level 4.The house was built in 2009 so not that old and I think it's fairly well insulated....
The worst of the complaints we received were from people who - like you - used them intermittently.
I'm not a big fan of heat pumps, all round, but they really don't work well or efficiently if they're switched off most of the time whilst people are out at work/asleep and are then called upon to ramp the temperature very quickly in mornings or evenings.
You could try managing the system differently, so that it is running continuously, at a low level - see if that improves the situation?
Equus said:
I've done estates around that date, with heating systems based on the Mitsubishi Ecodan, built to Code for Sustainable Homes Level 4.
The worst of the complaints we received were from people who - like you - used them intermittently.
I'm not a big fan of heat pumps, all round, but they really don't work well or efficiently if they're switched off most of the time whilst people are out at work/asleep and are then called upon to ramp the temperature very quickly in mornings or evenings.
You could try managing the system differently, so that it is running continuously, at a low level - see if that improves the situation?
Ok I've had a look and it's a Mitsubishi Zubadan...so I guess it's maybe an older model?The worst of the complaints we received were from people who - like you - used them intermittently.
I'm not a big fan of heat pumps, all round, but they really don't work well or efficiently if they're switched off most of the time whilst people are out at work/asleep and are then called upon to ramp the temperature very quickly in mornings or evenings.
You could try managing the system differently, so that it is running continuously, at a low level - see if that improves the situation?
Happy to change it around and run it for longer and see if that helps improve how well it works...what makes most sense? Have it on for all day or something?
mathmos said:
...what makes most sense? Have it on for all day or something?
You need to speak to a specialist in heat pump control systems; my interest and knowledge is limited to that of a specifier of such systems, and I rely on an specialist Energy Consultant to do the difficult sums for me when I'm designing one so take the following with a large pinch of salt. But as I understand it, there are two issues at play:1) Coefficient of Performance drops off as flow temperature increases, with a heat pump. So, in plain English, the harder you make it work, the less efficiently it will do so.
As an example, Mitsubishi claims that their Ecodan has a COP of about 5.3 (ie. you're getting 5.3 times as much energy out as the electrical energy you're putting in) when running at a flow temperature of 25 degrees C. This is just a few degrees warmer than you'll want your internal air temperature - so not much heat transfer will be taking place between your radiators and the air, and you'll be relying on the system working all the time, with low rates of heat loss through the fabric. If, on the other hand, you force it to supply a flow temperature of 60 degrees C, to rapidly boost the temperature of a house that's been sitting cold all day, the COP drops to something like 1.6. At this level you might as well be using storage heaters and Economy 7 tariff!
Depending on the energy efficiency of the building envelope (ie how good its insulation and airtightness is), there will be a 'sweet spot' between how long the ASHP is running and how hard it is working when it does run. Where that sweet spot lies is the $64 million question.To work it out accurately would require precise knowledge of a lot of factors, and some complicated maths, including calculus. Unless your controller is sufficiently 'intelligent' to do the maths for you, the best you can hope for is to get a feel for it by trial and error.
It's possible to build houses so well insulated, these days, that they barely need any heat input beyond solar gain and incidental gains from cooking, occupant bodyheat, etc. It is these properties where heat pumps can come into their own, as you can leave them running continuously at flow temperatures barely above the ambient room temperature (which most people will want to be between 18 and 22 degrees C), where they will deliver very good COP's. We're talking about properties with an airtightness 5 or 6 times as good as a typical 'developer' house mind you, and there are serious reservations to be considered in terms of air quality and occupant health in such dwellings, but that's a separate discussion.
2) Some systems have 'supplemental heat' functions where, if the heat pump is not supplying enough heat to meet the demand you place upon it, they will boost the output by means of a simple, direct electrical heating element. Some controller systems try to discourage the use of this by making it a manually selectable 'emergency boost', some do it automatically. If it's a manual override, then the emphasis should be on the word 'emergency': you're basically trying to warm your house up using an immersion heater, and it's hideously inefficient in this mode.
Equus...thanks for taking the time to type that up, really interesting and much appreciated!
I may try setting it up for running longer in the day, checking how much power was used then rinse/repeat to see if I can improve it. The house isn't really that cold at the moment so it shouldn't be working to hard to warm the place up, I also think the dial thermostats are a bit rubbish so I am going to get those replaced with a couple of nest devices this week to see if that helps the situation at all.
What really shocked me was how much electricity was used in the summer when the heating was off...again it maybe because it was working hard to heat the hotwater up again.
Some experimentation required!
I may try setting it up for running longer in the day, checking how much power was used then rinse/repeat to see if I can improve it. The house isn't really that cold at the moment so it shouldn't be working to hard to warm the place up, I also think the dial thermostats are a bit rubbish so I am going to get those replaced with a couple of nest devices this week to see if that helps the situation at all.
What really shocked me was how much electricity was used in the summer when the heating was off...again it maybe because it was working hard to heat the hotwater up again.
Some experimentation required!
Evoquative said:
Very non-expert on this, but believe it is also recommended to use a low temperature radiator for such installs, which are typically larger than a radiator to allow the lower temperature flow water to warm the room up.
Yes, absolutely: because they are more efficient at low flow temperatures, you need a larger surface area to transfer sufficient heat to the air. Underfloor heating is better still.Thread resuscitation!
Looked at a new build today, no gas on the site so all the houses have ASHP, Mitsubishi Ecodan. (Convection hob too, but that's another issue...)
Chilly day, so the agents had the heat on and the house was warm and cosy. Problem being something was emitting a loud humming which was audible in most rooms, especially the hallway.
I didn't have time to investigate exactly where the noise emanated from, but possible sources were
- Airing cupboard with cylinder, this didn't seem to be that loud when we checked inside
- Under stairs cupboard, my wife said there was something noisy in there but it was boxed in so hard to identify
- External fan units were quite loud, however the house seemed pretty well insulated so I wouldn't imagine it was exterior noise
Is this common with ASHP?
Looked at a new build today, no gas on the site so all the houses have ASHP, Mitsubishi Ecodan. (Convection hob too, but that's another issue...)
Chilly day, so the agents had the heat on and the house was warm and cosy. Problem being something was emitting a loud humming which was audible in most rooms, especially the hallway.
I didn't have time to investigate exactly where the noise emanated from, but possible sources were
- Airing cupboard with cylinder, this didn't seem to be that loud when we checked inside
- Under stairs cupboard, my wife said there was something noisy in there but it was boxed in so hard to identify
- External fan units were quite loud, however the house seemed pretty well insulated so I wouldn't imagine it was exterior noise
Is this common with ASHP?
As an aside, do you know if it was installed by an MCS accredited installer and if the kit is also same?
The reason is that there is an Renewable Heat Incentive where you can claim back some of the running costs. This often helps outset’s the higher capital costs when they are installed.
HP’s in the right situation can be a good solution and. The latest ones are getting more efficient.
Still better for commercial or multi-residential buildings.
The reason is that there is an Renewable Heat Incentive where you can claim back some of the running costs. This often helps outset’s the higher capital costs when they are installed.
HP’s in the right situation can be a good solution and. The latest ones are getting more efficient.
Still better for commercial or multi-residential buildings.
ChiefWiggum said:
External fan units were quite loud, however the house seemed pretty well insulated so I wouldn't imagine it was exterior noise
Is this common with ASHP?
Yes.Is this common with ASHP?
It was one of the reasons I designed what I called my 'Swiss Army Knife' for Code for Sustainable Homes... a brick housing that supported the rear of a carport (or integrated with the back of a garage) and neatly incorporated all the crap required for CfSH compliance (ASHP, cycle storage, composting bin, water butt, pull-out washing line).
It actually originated because of all the customer complaints we were getting about noise from external, free-standing Mitsubishi Ecodan ASHP's.
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