back2space
06-02-2013, 03:55 AM
I had my multi split LG inverter air con system installed in my new house in May last year. House is a 1930's end of terrace. Consists of a 9.38kw (FM25AH UE1) heating outdoor unit and 2 x 3.9kw (LIBERO range) (lounge & kitchen) & 2 x 2.1kw (LIBERO rang) (bedrooms) indoor wall mount units purposely oversized so the units can be run constantly in low fan speed. The system is used for cooling in the summer and heating in the winter.
The house also has a GCH system fitted radiators and combi boiler etc. Boiler approx 6 years old manufactured by Glow Worm & is 30kw in capacity.
Having done some tests to see which is cheaper this winter by trying to compare similar temperature weeks one week running GCH then one week running the air con system it appears that it is cheaper to run the GCH. The house gets upto temp quicker by using the air con system but as its warm air you dont get that nice radiant affect you get with radiators which seem to provide a more comfortable even heat and being under the windows they keep the room warmer and at a more consistant temp.
I can keep the flow temp of the rads down on the gas boiler to about 50C and the house maintains about 21C downstairs (TRVS open fully) and about 19C upstairs with the TRVs set lower as dont like it hot in bedrooms. With the air con system we have to have a set point of 22/23C in the downstairs rooms to compensate for the cooler areas near windows where the radiators normally stop any cool draughts from the windows. Bedrooms still set at 19C on the controllers the same as with the GCH. I found that with higher flow temps on the boiler to get the rooms upto temp quicker rooms end up feel stuffy even though TRVs are used reaction times are too slow so the rooms overheat when the TRV shuts off. So a lower flow temp means the boiler is just ticking over and the rooms dont tend to overheat but are slower to warm up but sometimes I turn the boiler up to get the house upto temp then reduce it right down. The air con doesnt even struggle on the colder days. Maybe I bump the fan speeds up a bit or start the upstairs units later once downstairs is close to set temp. When only one indoor unit is running there is a limit to what the outdoor unit can ramp down to so its usually best to have all 4 indoors running for max efficiency as the outdoor unit will still ramp down to the lowest setting and room temps are maintained. A multi unit is designed to run multiple units at the same time and not just one unit otherwise it becomes inefficient.
Cost of using air con per week during period (05th Nov - 24th Dec) ranges between £19-£26 (total elec usage for the house). Cost of using GCH per week during period (31st Dec - 4th Feb) is between £12-£19. Even when just using the air con system at temps below 5C outside I was still finding that I had to use the GCH radiator in the bathroom and the bottom of the stairs otherwise those areas were cold. This was costing £6-£8 per week on gas including the hot water rather than just the £4 for hot water. Over the summer gas usage is just for hot water and is approx £2-£3 per week, so about £2-£4 gets added on top if using the boiler to heat two radiators when using the air con system bringing the total to between £6-£8 for the week on gas alone.
On the weeks where GCH only was used my total electric consumption for the week cost between £10 & £13 as we have a tumble dryer also so some weeks this was used more. Its confused me with all the figures so maybe you can make more sense of the details I have profided. I have also attached my readings for the weeks so you can see roughly what I am using on the weeks without air con and with weeks of just using 2 radiators for the GCH. Above in bold are the dates I used air con and GCH so you can see from the attachments costs for those weeks.
Electric
http://i45.tinypic.com/1127p94.jpg
Gas
http://i49.tinypic.com/k4zgpi.jpg
There is much debate on if Air Con is cheaper to use for heating than GCH. Looking forward to your views. What do you think based on the data I have provided taking into account usage of electricity without the air con and usage of electric with air con etc.
Kind Regards
Richard.
The house also has a GCH system fitted radiators and combi boiler etc. Boiler approx 6 years old manufactured by Glow Worm & is 30kw in capacity.
Having done some tests to see which is cheaper this winter by trying to compare similar temperature weeks one week running GCH then one week running the air con system it appears that it is cheaper to run the GCH. The house gets upto temp quicker by using the air con system but as its warm air you dont get that nice radiant affect you get with radiators which seem to provide a more comfortable even heat and being under the windows they keep the room warmer and at a more consistant temp.
I can keep the flow temp of the rads down on the gas boiler to about 50C and the house maintains about 21C downstairs (TRVS open fully) and about 19C upstairs with the TRVs set lower as dont like it hot in bedrooms. With the air con system we have to have a set point of 22/23C in the downstairs rooms to compensate for the cooler areas near windows where the radiators normally stop any cool draughts from the windows. Bedrooms still set at 19C on the controllers the same as with the GCH. I found that with higher flow temps on the boiler to get the rooms upto temp quicker rooms end up feel stuffy even though TRVs are used reaction times are too slow so the rooms overheat when the TRV shuts off. So a lower flow temp means the boiler is just ticking over and the rooms dont tend to overheat but are slower to warm up but sometimes I turn the boiler up to get the house upto temp then reduce it right down. The air con doesnt even struggle on the colder days. Maybe I bump the fan speeds up a bit or start the upstairs units later once downstairs is close to set temp. When only one indoor unit is running there is a limit to what the outdoor unit can ramp down to so its usually best to have all 4 indoors running for max efficiency as the outdoor unit will still ramp down to the lowest setting and room temps are maintained. A multi unit is designed to run multiple units at the same time and not just one unit otherwise it becomes inefficient.
Cost of using air con per week during period (05th Nov - 24th Dec) ranges between £19-£26 (total elec usage for the house). Cost of using GCH per week during period (31st Dec - 4th Feb) is between £12-£19. Even when just using the air con system at temps below 5C outside I was still finding that I had to use the GCH radiator in the bathroom and the bottom of the stairs otherwise those areas were cold. This was costing £6-£8 per week on gas including the hot water rather than just the £4 for hot water. Over the summer gas usage is just for hot water and is approx £2-£3 per week, so about £2-£4 gets added on top if using the boiler to heat two radiators when using the air con system bringing the total to between £6-£8 for the week on gas alone.
On the weeks where GCH only was used my total electric consumption for the week cost between £10 & £13 as we have a tumble dryer also so some weeks this was used more. Its confused me with all the figures so maybe you can make more sense of the details I have profided. I have also attached my readings for the weeks so you can see roughly what I am using on the weeks without air con and with weeks of just using 2 radiators for the GCH. Above in bold are the dates I used air con and GCH so you can see from the attachments costs for those weeks.
Electric
http://i45.tinypic.com/1127p94.jpg
Gas
http://i49.tinypic.com/k4zgpi.jpg
There is much debate on if Air Con is cheaper to use for heating than GCH. Looking forward to your views. What do you think based on the data I have provided taking into account usage of electricity without the air con and usage of electric with air con etc.
Kind Regards
Richard.