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

richardc1983

helpjack wrote: »

The job for this year is to renovate our conservatory. It's approximately 6m X 3m with a thick polycarbonate roof glass on two sides and blank plastic on the side facing next door. All with drawf walls.

My plan was to replace the plastic roof with blue glass, replace the plastic wall with brick and heat it with one of these air to air inverters. I think a 12000 BTU one would be sufficient.

Do you think that would work. If we don't replace the plastic wall there is nowhere to hang the indoor unit.

I want it to be a dining room and playroom. I can't wait to get it useable.

Depends on many conditions, you'll probably find it does a good job but you will need to leave a night set back of say 16c if you plan to use it daily otherwise it will struggle to recover back to a comfortable temp.

zeupater

richardc1983 wrote: »

Depends on many conditions, you'll probably find it does a good job but you will need to leave a night set back of say 16c if you plan to use it daily otherwise it will struggle to recover back to a comfortable temp.

Hi

You'll probably find that with the total lack of any relevant thermal mass within the majority of the room it would be better to heat only when necessary & heating with a setback point would simply waste energy ....

HTH
Z

richardc1983

zeupater wrote: »

Hi

You'll probably find that with the total lack of any relevant thermal mass within the majority of the room it would be better to heat only when necessary & heating with a setback point would simply waste energy ....

HTH
Z

Quite possibly but if in use 12 hours a day but off over the night with the room getting to equalise the outside temp it will take all day trying to recover, wasting energy while you feel cold still as the fabric is so cold.

Set back maintains a base temp for comfort and quicker recovery at possibly an increase in energy. Mind you being inverter driven it will take little energy to run at 16c then when back to comfort temp e.g 19c it will not struggle so much and then be ticking along.

zeupater

richardc1983 wrote: »

Quite possibly but if in use 12 hours a day but off over the night with the room getting to equalise the outside temp it will take all day trying to recover, wasting energy while you feel cold still as the fabric is so cold.

Set back maintains a base temp for comfort and quicker recovery at possibly an increase in energy. Mind you being inverter driven it will take little energy to run at 16c then when back to comfort temp e.g 19c it will not struggle so much and then be ticking along.

Hi

What needs to be considered is the huge heatloss in a conservatory compared to a standard room in a modern insulated house and the issue of thermal mass.

A reasonable conservatory of the size being discussed is likely to lose heat at a rate of ~300-400W per hour per degree C difference between the internal & external temperatures ... with very little replacement heat being available from the mass of the construction (due to flimsy, low mass engineered construction), the vast majority of immediate heat replacement must be directly from the heating system .... at a particularly high overnight winter temperature of 4C, the thermal energy required to maintain a 16C setback for 12hrs would be somewhere between 40 & 60kWh.t, so the heatpump would consume ~10 - 15kWh of electricity, costing up to £3 overnight just to maintain the heat in an unused space ....

Now, based on the structure of the conservatory weighing 2tonnes (approx half of which is thermally separated), the energy required to return a 4C structure to 16C will be between 12 & 20kWh.t, so 3-5kWh of electricity through the heatpump, costing around 1/3 as much as maintaining heat in the unused space overnight with the low mass heat absorption resulting in a relatively low time to reach comfortable air temperatures the next day!

Remember, this is at an overnight 4C which would require a ~5kW heatpump to maintain at full power, so below this either you'd either need a larger heatsource or the temperature will simply reduce to an equilibrium point where heat supply matches loss ... for example, at -2C outside the 5kW heatpump would be working at full nominal power costing up to £5 overnight, yet the internal temperature would still fall to somewhere around 10C!

What possibly works in a highly insulated space with high thermal mass acting as a natural heat buffer needs to be reconsidered when thinking about relatively poorly insulated and low mass structures.

HTH
Z

matelodave

An air to air heatpump isn't like an ground source or airsource pump.

They are more like fan heaters so produce heat on demand and the heat output is much more controllable and they dont need to run continuously like an air/water based system and so would be much more effective in a conservatory type environment.

zeupater

matelodave wrote: »

An air to air heatpump isn't like an ground source or airsource pump.

They are more like fan heaters so produce heat on demand and the heat output is much more controllable and they dont need to run continuously like an air/water based system and so would be much more effective in a conservatory type environment.

Hi

Agree, effectively they heat the air directly through forced airflow, attaining levels of comfort relatively quickly, with that heat then heating the thermal mass ... underfloor heating heats the thermal mass and that mass passively warms the air to provide comfort, which is effectively what standard heating systems with radiators does too, resulting in a thermal delay when heating requirements are intermittent ... I'd maintain that conservatory use as a living area in winter would be at best intermittent therefore, in order to maintain energy efficiency & reduce bills, the heat source should also be able to react to intermittent demand quickly!

HTH
Z

helpjack

The existing plastic roof is life expired and is leaking quite badly. So I need to do something with this area. I can replace with a full extension but I don't want the expense or mess and I don't think the air to water heat pump that heats the rest of the house would stretch to the extra floor space. I can knock it down but that just seems a waste. Finally, I can renovate it and replace the leaking roof then I just need to finalize a way of heating it. Air to air seems the most efficient way with benefit of cooling in the summer. I would love to be able to use that room. It's a typical conservatory storage space at the moment with no heat source at all.

we could add electric underfloor heating but I imagine this is expensive to run although cheap to install.

We would mainly use it during the evening and weekends.

If it's really not worth spending the money maybe I hold out for a proper orangey type extension.

richardc1983

helpjack wrote: »

The existing plastic roof is life expired and is leaking quite badly. So I need to do something with this area. I can replace with a full extension but I don't want the expense or mess and I don't think the air to water heat pump that heats the rest of the house would stretch to the extra floor space. I can knock it down but that just seems a waste. Finally, I can renovate it and replace the leaking roof then I just need to finalize a way of heating it. Air to air seems the most efficient way with benefit of cooling in the summer. I would love to be able to use that room. It's a typical conservatory storage space at the moment with no heat source at all.

we could add electric underfloor heating but I imagine this is expensive to run although cheap to install.

We would mainly use it during the evening and weekends.

If it's really not worth spending the money maybe I hold out for a proper orangey type extension.

Underfloor electric heating will cost a bomb to run, as well as you having to leave it on 24/7 as it is so slow to react.

I would go with the heat pump maybe get a 5kw unit and then you can run it at lower fan speeds bumping it up when you need to when its really cold/hot.

helpjack

The conservatory is west facing so would get some heat gain on a sunny day even in winter especially with a glass roof I assume.

helpjack

Are there any recommendations for a suitable unit? Are they suitable for self install or does it need a professional. I'm sure I've read about pre gassed pipework? Thanks