UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

matelodave

I'm reading this with keen interest an I expect to be paying around £3-4 a day at this time of year for my electricity (heating, hot water, cooking, lighting, washing etc) because it's cold out side. On 30th Jan we used 53kw (£5.86), yesterday it was 28kw £3.09).

ASHP are sensitive to the outside temperature and us as much or as little as they need to maintain the flow temperatures required to keep the house warm.

I've got mine set up to be 40 degrees at -5 outside and 25 degrees at 20 degrees outside giving an average flow temperature of around 30-35 degrees. The internal thermostats are set to around 19 during the day/evening and 17 overnight.

This keeps the place nice and warm although I sometimes use the +5 degree flow temperature boost in the evenings if it's wet and windy when the house seems to cool faster by the evaporation of rain in the brickwork. We live in a 140m2 detached1986 bungalow in a very exposed area of Fenland in Cambridgeshire.

Hot water is set to 45 degrees and is only activated for two hours a day. The 200l tank gives us sufficient hot water for all our needs. Sterilisation to 60 degrees is performed once a week on Saturdays and this keeps the tank up to temperature so it doesn't need the Sunday morning heatup, thus not really costing all that much extra

richardc1983

Ok we've taken some figures for you. We have an energy meter on just the heat pump itself.

Night set back as confirmed yest is 18c. System comes on Sat mornings at 0600 and at 0735 this morning flow temp was at 44c outdoor unit was drawing 3.67kw with an outdoor temp of 0c. DHW is 47.6c.

All rooms downstairs at 19c upstairs landing the same. All trv's in used rooms are on full.

That's with a curve of 50c @ -6c set last night just before midnight. Electric usage since midnight was £1.33 so far upto 0735.

Make of that what you can but the house seems to be taking a while to warm up. Matelodave you have a very well performing system I think because you have underfloor heating so you can take advantage of the lower flow temps. My MIL has all radiators bar the hydronic kickspace fan heater in the kitchen.

matelodave

Our place takes ages to warm up because of the low flow temperatures - a couple of years ago I shut it down for a fortnight in December whilst we went away and it must have take 36 hours for the place to recover (it was knee deep in snow outside though).

Ours is on continuously but under control of the room stats which controls the circulation pump and I assume has a boiler interlock because if there's no call for heat then the flow temperature drops down towards 25 degrees.

We have u/f heating in all rooms and each room has it's own programmable stat which controls the water flow in the heating loop and can turn the "boiler" on and off - so if just the bathroom needs heat it can control the system.
For instance the bathroom set back is 17 degrees with an up lift to 19 between 0700 and 0900 and 2000 and 2200 every day whereas the lounge is 19 degrees between 0700 and 2200 with a set back to 17 over night.
I was late in the bathroom this morning at 1000 and the thermometer showed it to be 17.8 in there but the floor was still warm and it was perfectly comfortable to be undressed & showering - even my wife who is the ultimate chilly mortal is quite happy with the house temperatures.

It seemed to be everso cold outside last night as we've already used about 20kw/h since midnight see here http://www.energyhive.com/dashboard/dave for our energy consumption - you can see that the heating kicked in at about 2am and then started working quite hard at about 0315 and ran virtually all night which is fairly unusual. The normal pattern is short zig-zags unless there is a big call for heat.

richardc1983

MIL system is constanly on. 0600-0900 @ 21c and then 1700-2200 @ 21c all other times it is set back to 18c.

lovesgshp

Have been looking at the curve graph you sent and compared some settings with the models we use.
At 0C then they are reading approx 44C flow, as yours is as well. With the Samsung, it ramps up quite highly on the -2c setting, whereas with the -6C it is a slower curve.
What sort of external temps are you getting e.g daytime, overnight at the moment?

richardc1983

lovesgshp wrote: »

Have been looking at the curve graph you sent and compared some settings with the models we use.
At 0C then they are reading approx 44C flow, as yours is as well. With the Samsung, it ramps up quite highly on the -2c setting, whereas with the -6C it is a slower curve.
What sort of external temps are you getting e.g daytime, overnight at the moment?

This morning it was 0 at 0735, and at present were on 2c but it has been about 5c today with the winter sunshine but heating hasn't been on since this morning other than the 18c set back. The other day was about 6c but then when sun comes out it goes up think we reached 9c one day this week. Used £2.73 since midnight and outdoor unit drawing 2.82kw. Most rooms upto 19c so far it's been on since 5pm @21c set point. Flow temp is 43.6c return temp is 35.7c. We're quite high up and not far from Leeds/Bradford Airport.

Haven't managed to look at the software you sent yet as my laptop is playing up and I just use the iPad to post on here!

lovesgshp

Is the setback decided by the room temperature or by flow temperature within the pump?

richardc1983

lovesgshp wrote: »

Is the setback decided by the room temperature or by flow temperature within the pump?

We have a programmable thermostat in the hall that we choose to have set back to 18c I think if the system comes on during the set back the flow temp would be the same as any other time as the controller just sends a demand for heating.

lovesgshp

Is there a flow temperature timer on the pump controller? e.g with mine, I can reduce the return pump temp overnight by XC. Therefore it does not need to work so hard in the morning to get back to heat.

richardc1983

lovesgshp wrote: »

Is there a flow temperature timer on the pump controller? e.g with mine, I can reduce the return pump temp overnight by XC. Therefore it does not need to work so hard in the morning to get back to heat.

Nothing like that no