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

ian103 wrote: »

Just thought Id report back, after obtaining quotes for air to water, air to air, oil and replacement LOT 20 storage heaters, we opted for air to air. We had a mixed response as to whether the property was suitable for air to water so we dismissed this option (if we had been installing underfloor heating it would have been a good option) Well the impresssions after a month are good, property is finally warm this year after 5 bad years with storage heaters. Its controllable, reasonablly economic, its costing more than the old E7 heaters but we are no longer reliant on the log burner to keep the house warm. I dont think its for everyone but it works for us.

Hi Ian

Good to hear. What kind of units did you end up going for?

Richard.

treecol wrote: »

After getting our air to air unit installed back in the year, we had a lovely cool summer and now are getting used to using the unit for heat. Certainly when the weather was cold, it took longer for the room to get warm so we are learning as we go. Just wonder if - and I know this is probably a really dumb question, but if I increase the temperature on the unit from say 18 degrees to 24, will the unit use more electric? I notice when I first increase the temp, the motor outside seems to be working harder then seems to settle, so just wondering as I don't really know how these things work at their most efficient.

The unit will work harder like using the accelerator in your car. If your cruising along at 40 (18c) and then want to go to 70 (24c) you put your foot on the gas. An inverter unit will put it's foot to the floor to get to your chosen temp asap, once it's there it will take it's foot off and just use enough power to keep the temp there.

A normal unit will floor it each time overshooting the set temp by 1c at full power then turn off room temp then drops 1c below the set temp then it will come back on and floor it at full power. Anything over your set temp is wasted energy so an inverter avoids this by slowing it's compressor down. Saving energy. Of course set it so it's comfortable but 24c does seem high, 22c is usually the comfortable temp and once it's achieved it will slow down the compressor however the heat loss from your house at 24c is higher than at 18c so it has to run faster to maintain the higher temp.

Ensure your night setback temps when your in bed or not at home don't go below about 18c otherwise the unit will be running at full throttle for a long time to achieve your set temp.

Are you putting it Upto 24c at night or leaving it at 18c? A heat pump the lowest temp should be about 18c again it's all down to comfort. You would have to try it and see.

treecol wrote: »

No, just leaving it at 18c in the evening - we don't leave it on overnight. So that's what I'm trying to determine - do we leave it on at 18c all the time or turn only turn it on when we're in the house but off overnight.
We're currently using it as we would our warm air central heating and only having it on when we're home during waking hours. But I'm getting the impression they are more efficient if used differently?

Do you find the house comfortable at 18c, its not that cold yet so quite mild and really depends how well insulated your house is. A set back time for unoccupied times is how you would run underfloor heating. E.g if you turned off completely and your house dropped down to 10c in the night then it will take a long time to get back up to 18c.

If 18c is your comfort temperature when you turn it on and your happy and warm at that then you could set back to 16c and that way its keeping a base temperature. If for example you turn it to 21c when your in (if thats your comfort temp) and then turn it off we would recommend that you turn it down to 18c when unoccupied so the house envelope and structure is not dropping too low. The unit then doesn't need to work as hard to get back up to your comfort temp.

When a heat pump starts from cold so say 10c in the house and its cold outside the unit has to work really hard and at full output to get back to your comfort temperature, units that are borderline undersized may never achieve that temperature when it is really cold. When a unit is working really hard frost build up increases on the outdoor unit and defrosting can become frequent especially when the air is damp and cold. The greater the difference between the comfort temp and the actual return air temperature at the unit means the unit is having to work harder for longer to get to there.

While the unit is in defrost cycle there is no heat being blown out of the indoor unit as the system goes into reverse to defrost the outside unit.

All depends on what you are comfortable with, base it on your comfort temperature that you set it at when you are in the house. It may be that you have an ultra modern house that keeps the heat in, so you set it back to 18c and your house doesn't drop below that naturally in the night before you turn it back up to your comfort temperature then your saving energy and it just has to put the work in to get back to your comfort temperature of say 21c.

If for example you don't use a night set back, live an old, poorly insulated cold house and your comfort temp is 21c and in the night the house drops to 10c. When you turn the unit back on the next morning its going to take a long time to get back up to 21c, depending on how cold it is outside and how much moisture is in the outdoor air. From a comfort perspective also this is not great. The unit will ramp right up to full output until it gets close to the comfort set temp. Using night set back of say 18c if the house drops below 18c the unit will come on and put just enough heat into the house to maintain that, the outdoor unit will be ticking away gently.

It's also kinder on the components not to be running flat out and just ticking along.

I will reiterate, if you are comfortable at 18c, then try a lower night set back e.g 16c which is the lowest recommended temperature for health. I wouldnt leave it at your comfort temperature 24/7. That would be like your comfort temperature being 22C and heating the house to that 24/7, it will waste energy while you are tucked up in bed. The trick is to keep the house from getting too cold. Set back is usually 2-3c lower than your usual temperature.