ASHP. We've only gone and done it again!

lovesgshp

Swipe wrote: »

I'd be interested if you could outline how this new installation differs from the original set up.

Would think the original was set up by plonkers trying to get into the market without a clue. 1 day training and then experts!!!

TiredGeek

HappyMJ wrote: »

I'm a little lost here. This is a 170 square metre house. More than twice as big as the "average" UK house of 80 square metres. The "average" UK house uses 16,500kWh of gas for heating, hot water and cooking. I would say you would use double based on that standard. However, the system also has about 31 radiators which is triple the "average" UK GCH installation so the system would use triple based on that standard. The "average" UK house is now quite well insulated hence the recent reductions of the average gas usage from 20,500kWh to 16,500kWh and you have solid stone walls which will increase consumption over the "average". You also live in a very cold region which will also increase the average. It's also detached where the "average" UK house is semi-detached.

If the SAP report says your house will require 291kWh/m2/year then why is that figure incorrect? What should it be? The average for GB is 198kWh/m2/year.

I can't see the usage dropping much below 100kWh/day (on a cold day) as you had with the previous system....at 13p/kWh for electric as you have quoted in a previous thread that would cost £13 per day. Over 6 months of the heating season that's 18,250kWh for heat (outputting at least double due to COP rating of 2 at 36,500kWh per year) plus hot water and normal electric usage.

System looks very impressive...hope it's worth it in the long run.

OK, I'm not going to pretend I understand all the calculations, but there's been a second, much more thorough inspection carried out and then calculations were done. Results are thus:

Heat Pump Space Heating Mode Annual Space Heating Energy Requirement (kWh) 59414
Annual Space Heating Energy Consumption (kWh) 16975
Annual Cost of Space Heating from Heat Pump £2,037.04
Annual Space Heating CO2 Emissions of Heat Pump (kg CO2) 8810

Heat Pump Hot Water Mode
Daily Energy Requirement for Water Heating (kWh) 11.77
Total Energy to be delivered to Cylinder Daily (kWh) 12.35
Total annual hot water demand (kWh) 4509
Annual Energy Consumption (kWh) 1961
Annual Cost of Hot Water Heating from Heat Pump £235.26 Annual Hot Water CO2 Emissions of Heat Pump (kg CO2) 1018

Total annual energy requirement of dwelling (kWh) 63923
Total annual energy consumption of Heat Pump System (kWh) 20026
Total annual run cost for Heat Pump System £2,403.15
Total annual Heat Pump System CO2 Emissions (kg CO2) 10394

With the same numbers oil would come in at £5935!
It's looking very much like the previous £13/day is actually a probability, however, the old system never actually made it through a winter without failing horribly. This one is pretty much guaranteed to survive Also, that £13/day previously was when the system was trying to keep the house at 10'c frost setting...
Hopefully it will come in at less than expected running costs as we tend to keep the house cooler than the temps the calculations were based on, but we'll give it a full twelve months before we work out the numbers.

BTW, there's now 39 radiators fitted (! couldn't find room to round it up to 40 )

TiredGeek

Swipe wrote: »

I'd be interested if you could outline how this new installation differs from the original set up.

Basically, they've optimised flow rates through the heat pumps and around the radiators to ensure there is good flow at all times. They've fine tuned the settings of the units and actually calculated pipe sizes and flow rates so that everything can work as well as possible.
It is down to attention to detail. Fundamentally the system is the same as before - same ASHP, same water pumps, but fitted and optimised better.

Now that it's monitored we'll be able to see if there's any area that can be improved, and we'll have early warning of problems. We won't have to wait 'till they fail

lovesgshp

Calculations seem ok, hot water seems high, but you have longer low temps than us. Hope the figures come in to plan.
Is it 28Kw setup again?
What size buffer tank for the rads?

HappyMJ

TiredGeek wrote: »

OK, I'm not going to pretend I understand all the calculations, but there's been a second, much more thorough inspection carried out and then calculations were done. Results are thus:

Heat Pump Space Heating Mode Annual Space Heating Energy Requirement (kWh) 59414
Annual Space Heating Energy Consumption (kWh) 16975
Annual Cost of Space Heating from Heat Pump £2,037.04
Annual Space Heating CO2 Emissions of Heat Pump (kg CO2) 8810

Heat Pump Hot Water Mode
Daily Energy Requirement for Water Heating (kWh) 11.77
Total Energy to be delivered to Cylinder Daily (kWh) 12.35
Total annual hot water demand (kWh) 4509
Annual Energy Consumption (kWh) 1961
Annual Cost of Hot Water Heating from Heat Pump £235.26 Annual Hot Water CO2 Emissions of Heat Pump (kg CO2) 1018

Total annual energy requirement of dwelling (kWh) 63923
Total annual energy consumption of Heat Pump System (kWh) 20026
Total annual run cost for Heat Pump System £2,403.15
Total annual Heat Pump System CO2 Emissions (kg CO2) 10394

With the same numbers oil would come in at £5935!
It's looking very much like the previous £13/day is actually a probability, however, the old system never actually made it through a winter without failing horribly. This one is pretty much guaranteed to survive Also, that £13/day previously was when the system was trying to keep the house at 10'c frost setting...
Hopefully it will come in at less than expected running costs as we tend to keep the house cooler than the temps the calculations were based on, but we'll give it a full twelve months before we work out the numbers.

BTW, there's now 39 radiators fitted (! couldn't find room to round it up to 40 )

OK that makes sense they have now used an average COP of 3.5 for heating and 2.3 for hot water which in my opinion based on what you have said so far will only work if you live in a fairly mild area of the UK or as long as the weather is mild which last year it was.....but...then they have used a heating value of 350kWh/m2/year (assuming 170m2). Probably to compensate for the higher COP value. It's still £11 per day just for heating which is the annual heating bill divided out over 6 months. They have now also used 12p/kWh. Is that the actual (including VAT rate) charged on your bill? You previously have said your rate is 13p which would be 12.4p (ex VAT) which is a reasonable rate.

The temperatures are based on getting living spaces and bathrooms to maintain 21 degrees and other spaces to 18 degrees running 24/7 they do knock a few degrees off at night.

I think most people would have a heart attack even if this house was run on gas and the gas bill came in at 80,000kWh (using an 80% efficient boiler) then plus gas for cooking and electricity usage but it is a big old not very well insulated house.

lovesgshp

HappyMJ wrote: »

OK that makes sense they have now used an average COP of 3.5 for heating and 2.3 for hot water which in my opinion based on what you have said so far will only work if you live in a fairly mild area of the UK or as long as the weather is mild which last year it was.....but...then they have used a heating value of 350kw/m2/year (assuming 170m2). Probably to compensate for the higher COP value. It's still £11 per day just for heating which is the annual heating bill divided out over 6 months. They have now also used 12p/kWh. Is that the actual (including VAT rate) charged on your bill? You previously have said your rate is 13p which would be 12.4p (ex VAT) which is a reasonable rate.


The temperatures are based on getting living spaces and bathrooms to maintain 21 degrees and other spaces to 18 degrees running 24/7 they do knock a few degrees off at night.
20c normally

I think most people would have a heart attack even if this house was run on gas and the gas bill came in at 80,000kWh (using an 80% efficient boiler) then plus gas for cooking and electricity usage but it is a big old not very well insulated house.

Most thermal calcs would be based on 20C internal temps. Over that running costs start to increase. TG has not said the water temp setting for DHW, but it is early days for the system, so think he will have a better idea in the cooler months.
My GSHP is only running 4 hrs a week now for hot water.

HappyMJ

Geotherm wrote: »

Most thermal calcs would be based on 20C internal temps. Over that running costs start to increase. TG has not said the water temp setting for DHW, but it is early days for the system, so think he will have a better idea in the cooler months.
My GSHP is only running 4 hrs a week now for hot water.

OK I'll go with 20C (averaged over the 24 hours)...and GSHP's are more efficient than ASHP's as the ground temperature is higher than the air temperature. I think it's been said on a previous thread the setting was 35C. A COP for heating of 3.5 would be based on outside average temperatures being about 7C. That isn't going to happen in winter any part of the UK. I live in a fairly mild area of the Midlands and the average air temperature in what was a mild month of Jan 2012 was 5C...April 2012 was 7C.

lovesgshp

HappyMJ wrote: »

OK I'll go with 20C (averaged over the 24 hours)...and GSHP's are more efficient than ASHP's as the ground temperature is higher than the air temperature. I think it's been said on a previous thread the setting was 35C. A COP for heating of 3.5 would be based on outside average temperatures being about 7C. That isn't going to happen in winter any part of the UK. I live in a fairly mild area of the Midlands and the average air temperature in what was a mild month of Jan 2012 was 5C...April 2012 was 7C.

Rad temps are not based on 35C, that is underfloor, the OP has rads Yes, ASHP cops are worked on 7C outside temps. COP will reduce as the temps get lower. .

HappyMJ

Geotherm wrote: »

Rad temps are not based on 35C, that is underfloor, the OP has rads Yes, ASHP cops are worked on 7C outside temps. COP will reduce as the temps get lower. .

So doesn't that mean the higher the water temperature then the lower the COP? Like what they have used with the hot water with a COP of 2.3 which would require water temperatures of 70C. I'm just saying that a COP of 3.5 for central heating is not going to very achievable unless it's spring or autumn when central heating isn't required as much. I would guess the COP will be much lower than 3.5 in winter on a very cold evening when the heat demand is the highest. If it's lower than minus 10C outside then it's likely the COP of an ASHP will be close to 1.0.

lovesgshp

HappyMJ wrote: »

So doesn't that mean the higher the water temperature then the lower the COP? Like what they have used with the hot water with a COP of 2.3 which would require water temperatures of 70C. I'm just saying that a COP of 3.5 for central heating is not going to very achievable unless it's spring or autumn when central heating isn't required as much. I would guess the COP will be much lower than 3.5 in winter on a very cold evening when the heat demand is the highest. If it's lower than minus 10C outside then it's likely the COP of an ASHP will be close to 1.0.

Yes, as the outside air temp reduces, the COP lowers. 70C is high for a rad system, it is usually based @ 55C. A buffer tank is normal for rad systems, to stabilise the heat level.