Fitted Air conditioning

[Flumpo]

Accidentally done a practical comparison…

Turned on the hot air on Wednesday, set to 22 degrees and fan setting 1 of 5. Erm, then forget, went away and just got back. That’s from 9 am ish on Wednesday until about 10 mins ago.

Phantom load was 3p and hour before it was turned on, then a steady 10/11p per hour after that. So costs about 7p to run at that setting. According to the thermometer downstairs was a fairly nice temp the whole time:







A lot cheaper than when the wife left the gas heating on when she went to work!

That was a steady 28p an hour after initial fire up of 42p!

[LocoBlade]

LastPoster said:

Its more efficient for the compressor to run at part load to meet demand than run at full speed then shut off and restart again. Once it's approaching your desired temperature it will start to slow up and once stabilised will be meeting the heat loss of the space

ETA 700W at 'full load' seems a bit low for a 3.5kW unit. There are a lot of variables but I would have expected it to be more like 900/1000W

Cheers, yep I think you're right, it's more like 1kw initially when the room was really cold rather than starting at ~15c as it was when I did my test, so I guess idling at 5-700kw is modulating down somewhat and from the looks of the other posts above that's about par for the course, I guess I was expecting it to cut in and out more a bit like a thermostatically controlled oil rad or fan heater would.

[Shnozz]

Lazy on my part but what’s the conclusion? Air con is more effective and cheaper to run for heating than GCH?

I ask as I weigh up limited options (electric only).

[LastPoster]

LocoBlade said:

Cheers, yep I think you're right, it's more like 1kw initially when the room was really cold rather than starting at ~15c as it was when I did my test, so I guess idling at 5-700kw is modulating down somewhat and from the looks of the other posts above that's about par for the course, I guess I was expecting it to cut in and out more a bit like a thermostatically controlled oil rad or fan heater would.

20 years ago it would have

[LocoBlade]

Flumpo said:

Accidentally done a practical comparison…

Turned on the hot air on Wednesday, set to 22 degrees and fan setting 1 of 5. Erm, then forget, went away and just got back. That’s from 9 am ish on Wednesday until about 10 mins ago.

Phantom load was 3p and hour before it was turned on, then a steady 10/11p per hour after that. So costs about 7p to run at that setting. According to the thermometer downstairs was a fairly nice temp the whole time:


A lot cheaper than when the wife left the gas heating on when she went to work!

That was a steady 28p an hour after initial fire up of 42p!

That presumably isn't comparing apples with apples though, the air con unit is heating one room whereas the central heating is heating the whole house?

[colin_p]

For those who intend to use their systems for heating, be aware that when it is very cold outside, the outside units ice up.

I had this last winter, which wasn't particularly cold. The system will sort this out by again reversing the flow back into internal cooling mode and then back again to heating mode.

It takes my system about 20 mins to do the de-ice.

[LastPoster]

Shnozz said:

Lazy on my part but what’s the conclusion? Air con is more effective and cheaper to run for heating than GCH?

I ask as I weigh up limited options (electric only).

Way too many variables for anyone to give you an answer

The performance people are quoting here would be massively different if the outdoor air temp was -5C. A gas CH system costs much the same to run regardless of outdoor temp (it will run more obviously but the actual cost per kW of heat put into the space will be much the same)

It feels more effective, more quickly as the air movement is dynamic (fan assisted) not passive like a radiator. That's great when the air temp emitted by the system is high enough but causes all sorts of issues when it's lower in times of low internal and/or external temps

Heating a single room using a single AC unit is probably more effective (not necessarily efficient) than running a LTHW (regardless of what heats the water) system to heat a single rad with the rest shut down by smart TRVs

[Flumpo]

LocoBlade said:

Flumpo said:

Accidentally done a practical comparison…

Turned on the hot air on Wednesday, set to 22 degrees and fan setting 1 of 5. Erm, then forget, went away and just got back. That’s from 9 am ish on Wednesday until about 10 mins ago.

Phantom load was 3p and hour before it was turned on, then a steady 10/11p per hour after that. So costs about 7p to run at that setting. According to the thermometer downstairs was a fairly nice temp the whole time:


A lot cheaper than when the wife left the gas heating on when she went to work!

That was a steady 28p an hour after initial fire up of 42p!

That presumably isn't comparing apples with apples though, the air con unit is heating one room whereas the central heating is heating the whole house?

air con was 2 living rooms that connect and kitchen, not sure what the kitchen temp was. Gas was 1 zone 2 bedrooms.

[LocoBlade]

I think they could be competitive with air source air-water heat pumps and gas central heating but personally I wouldn't want an entire house heated by air con units because as well as the fan noise (not loud but certainly not silent), they naturally create a lot air movement in the room which isn't as comfortable to live in as a room with radiators or even better, underfloor heating. However, if an air source heat pump running conventional water radiators etc wasn't an option and it was a choice of air con units or other electric heating options like electric radiators etc, I would go with air con units because they'll be about 3-4x cheaper to run for a given heat output compared to conventional electric heaters.

[Flumpo]

LocoBlade said:

I think they could be competitive with air source air-water heat pumps and gas central heating but personally I wouldn't want an entire house heated by air con units because as well as the fan noise (not loud but certainly not silent), they naturally create a lot air movement in the room which isn't as comfortable to live in as a room with radiators or even better, underfloor heating. However, if an air source heat pump running conventional water radiators etc wasn't an option and it was a choice of air con units or other electric heating options like electric radiators etc, I would go with air con units because they'll be about 3-4x cheaper to run for a given heat output compared to conventional electric heaters.

Agreed really, my choice would go, central heating, decent gas fire, air con, real fire, air source heat.

Can’t describe what, but the heat is better from central heating. Don’t know why, just feels better to me!

[LocoBlade]

Flumpo said:

air con was 2 living rooms that connect and kitchen, not sure what the kitchen temp was. Gas was 1 zone 2 bedrooms.

Seems a lot of gas just to heat two bedrooms in the middle of October, we used less than that (35KWh) to heat an entire 80's vintage 4 bed detached house to 20c on that same day a couple of weeks back.

Edited by LocoBlade on Thursday 27th October 20:21

[Flumpo]

LocoBlade said:

Flumpo said:

air con was 2 living rooms that connect and kitchen, not sure what the kitchen temp was. Gas was 1 zone 2 bedrooms.

Seems a lot of gas just to heat two bedrooms in the middle of October, we used less than that (35Kw) to heat an entire 80's vintage 4 bed detached house to 20c on that same day a couple of weeks back.

If you know anything about gas boilers I am more than happy for you to come and look? 3 different people can’t figure out why it’s dropping pressure.

[Matt p]

colin_p said:

For those who intend to use their systems for heating, be aware that when it is very cold outside, the outside units ice up.

I had this last winter, which wasn't particularly cold. The system will sort this out by again reversing the flow back into internal cooling mode and then back again to heating mode.

It takes my system about 20 mins to do the de-ice.

That’s an awfully long defrost cycle, may I ask it’s location in relation to the wind direction against it?. Also how many cycles does it go through over a 24hr period?.

[LocoBlade]

Flumpo said:

If you know anything about gas boilers I am more than happy for you to come and look? 3 different people can’t figure out why it’s dropping pressure.

There'll be a small water leak in the heating system somewhere, might be in the boiler itself, might be in the pipework under the floor but not enough to cause a damp spot so very difficult to find. Annoying if it can't be located but if all else fails you could try something like this, the equivalent of a rad weld for heating ( https://www.screwfix.com/p/flomasta-0647-central-h...) . Either way though it won't significantly affect how much gas you're using

[Flumpo]

LocoBlade said:

Flumpo said:

If you know anything about gas boilers I am more than happy for you to come and look? 3 different people can’t figure out why it’s dropping pressure.

There'll be a small water leak in the heating system somewhere, might be in the boiler itself, might be in the pipework under the floor but not enough to cause a damp spot so very difficult to find. Annoying if it can't be located but if all else fails you could try something like this, the equivalent of a rad weld for heating ( https://www.screwfix.com/p/flomasta-0647-central-h...) . Either way though it won't significantly affect how much gas you're using

Gutted now, I was really smug how much I had got the usuage down from last year.

[NMNeil]

Matt p said:

colin_p said:

For those who intend to use their systems for heating, be aware that when it is very cold outside, the outside units ice up.

I had this last winter, which wasn't particularly cold. The system will sort this out by again reversing the flow back into internal cooling mode and then back again to heating mode.

It takes my system about 20 mins to do the de-ice.

That’s an awfully long defrost cycle, may I ask it’s location in relation to the wind direction against it?. Also how many cycles does it go through over a 24hr period?.

I wondered that as well.
My units will slowly ramp down when it shows df (defrost) on the indoor unit. Takes just a few minutes for it to de-ice and come back on, no matter how cold it is outside.

[Shnozz]

LastPoster said:

Way too many variables for anyone to give you an answer

The performance people are quoting here would be massively different if the outdoor air temp was -5C. A gas CH system costs much the same to run regardless of outdoor temp (it will run more obviously but the actual cost per kW of heat put into the space will be much the same)

It feels more effective, more quickly as the air movement is dynamic (fan assisted) not passive like a radiator. That's great when the air temp emitted by the system is high enough but causes all sorts of issues when it's lower in times of low internal and/or external temps

Heating a single room using a single AC unit is probably more effective (not necessarily efficient) than running a LTHW (regardless of what heats the water) system to heat a single rad with the rest shut down by smart TRVs

Thank you. Useful response. Going to continue to investigate. I installed infra red heaters last year and haven’t been too impressed. I have air con in the bedrooms and office of a house abroad and find them excellent for heating in winter as well as cooling in summer. U.K. property doesn’t need any cooling but for a heating fulfilment it might be a good solution and not crazy electric prices.

[caziques]

Just be warned

Air conditioners are great for raising or lowering the air temperature a few degrees, and obviously they are even better on cooling as they move air around (so providing a draught).

However, they are very poor at providing true comfort in winter when it's cold outside.

The performance drops off just when you need more, they have to reverse and defrost every half an hour, and they only work by moving air, which is draughty.

Human comfort for heating, is mostly from radiant heat.

Consider a room at 10 degrees, where everything is 10 degrees. Change the air for 25 degrees, the room will still feel uncomfortable until all the furniture etc etc has warmed up.

So by all means fit a heat pump, but realize the limitations.

[LocoBlade]

Shnozz said:

Thank you. Useful response. Going to continue to investigate. I installed infra red heaters last year and haven’t been too impressed. I have air con in the bedrooms and office of a house abroad and find them excellent for heating in winter as well as cooling in summer. U.K. property doesn’t need any cooling but for a heating fulfilment it might be a good solution and not crazy electric prices.

As you've seemingly discovered, infrared won't put out any more heat than an oil filled radiator or fan heater because anything with some kind of element converting electric directly into heat will give out the same amount of heat energy for a given power consumed (its a straight 1kw in = 1kw out 100% efficiency). Because heat pumps like air con units extract heat energy from the surrounding air and only use electricity to power the compressor pump etc, they can output 3-5x the amount of heat energy compared to the amount of power consumed.

[LastPoster]

Infrared is different to an oil filled rad or electric heater in as much as it heats things not air. The second you turn it off, whatever (normally people) you have been heating will immediately feel cold again. It will warm a space by whatever it is heating getting warm and releasing that heat but that's not an efficient way of heating

Works well as a patio heater or to spot heat a warehouse where the packers sit, but not the entire place