All a load of COP?!

blast06

Hi,

As a few may have seen from other threads, i'm in the middle of a new build and still undecided re borehole geothermal versus air to water heat pump..... have plumbed for both but vearing very much towards air to water due to cost of drilling (horizontal geothermal not an option due to gravel base all around house).

Anyway, question is re the COP of the heat pump.
What i hadn't considered when looking at the COP for an air to water pump is whether it can increase above the 'advertised' during the summer months. This obviously is not for house heating purposes at that time of the year but more for hot water .... which i have been advised can be over 50% of the annual electricity bill contribution from your heat pump in a part L 2011 house.

In simple terms, if the air to water heat pump you have has an advertised COP of say 4 (which is based on an outside air temp of 7 degrees heating up water to 35 degrees), then will you still get a COP of 4 if you are heating up to 45 degrees with air temp of 17 degrees ?

Cheers.

Condenser

blast06 wrote: »

Hi,

As a few may have seen from other threads, i'm in the middle of a new build and still undecided re borehole geothermal versus air to water heat pump..... have plumbed for both but vearing very much towards air to water due to cost of drilling (horizontal geothermal not an option due to gravel base all around house).

Anyway, question is re the COP of the heat pump.
What i hadn't considered when looking at the COP for an air to water pump is whether it can increase above the 'advertised' during the summer months. This obviously is not for house heating purposes at that time of the year but more for hot water .... which i have been advised can be over 50% of the annual electricity bill contribution from your heat pump in a part L 2011 house.

In simple terms, if the air to water heat pump you have has an advertised COP of say 4 (which is based on an outside air temp of 7 degrees heating up water to 35 degrees), then will you still get a COP of 4 if you are heating up to 45 degrees with air temp of 17 degrees ?

Cheers.

At 17C and 45C outlet your COP should be even slightly higher, closer to 5 in those conditions. I say should because your COP relies as much on the knowledge of your installer as on the equipment itself.
Your hot water should be nowhere near 50% of your total bill. Closer to 20%.
Also take note that your COP will drop way below 4 in cold weather and quoted COP's do not include defrosts or any backup that may be required by the immersion.

fclauson

for my house I am finding that I am using about equal Kwh primary for heating and hot water
Jan to March average electricity usage
Heating 10.4Kwh/day
H/w 8.4 Kwh/day

the cost is hard to calc as I am using some night time rate, some day time rate and some solar PV - but say its 20Kwh/day @ approx 10c per unit then its €2/per day

or to better express the heating element (all of primary electricity not of delivered energy)
Jan 35 w/m2/day (PHPP gives 97)
Feb 28 w/m2/day (PHPP gives 73)
Mar 28 w/m2/day (PHPP gives 38) - March was very cold

blast06

Thanks for comments guys.
I guess the key 'discovery' here for me is that the COP can be higher right throughout the summer months when you'd be interested in hot water only for 90% of the time.

I guess the percentage of energy use for heat versus hot water very largely depends on the occupants .... a sporty young couple (showers after gym) versus say a family with 3 or 4 teenage daughters !!

fcaluson ... i guess if it is close to 50:50 in Jan-March then on an annual level it probably is close to 60:40 in favour of hot water (but i know your house is passive A1) ?
Also, to just sanity check my calculations - is you house between 3500 and 4000 sq ft ?

fclauson

blast06 wrote: »

I guess the percentage of energy use for heat versus hot water very largely depends on the occupants .... a sporty young couple (showers after gym) versus say a family with 3 or 4 teenage daughters !!

also we have a hot water return from the kitchen (house is a broken "L" design" and kitchen is a long way from tank) this certainly makes our h/w usage a little higher

fcaluson ... i guess if it is close to 50:50 in Jan-March then on an annual level it probably is close to 60:40 in favour of hot water (but i know your house is passive A1) ?
Also, to just sanity check my calculations - is you house between 3500 and 4000 sq ft ?

yes - which is why I converted it to w/m2/day to remove the size piece

sinnerboy

Heat pumps are listed on the SEAI harp database indicating their SPF ( Seasonal Performance Factor ) which is derived from (various ISO accreditated lab tested) COP's for that heat pump.

Here is an example of test data for several Air to Water heat pumps. Notice how when talking about COP one must reference the ambient air temperature and the temperature of the water heated by the heat pump. Not surprisingly the COP improves when the ambient air temperature increases and/or when the temperature of the water heated by the heat pump decreases.

Here are SEAI's rules for arriving at the SPF. Depending on the type of heat pump the tested COP's are adjusted or aggregated into one figure the SPF for use in DEAP.

But to answer the OP query one should seek out the range of COP's as determined by testing according to EN 14511, EN 16147 and EN 255-3:

For further test results look here

sinnerboy

Whilst test results are very useful to compare Heat Pump A vs Heat Pump B , as condenser has touched upon earlier , establishing this data alone will not give you the full picture of your installation.

The electrical consumption demanded of your heating distribution pump cannot be accounted for in a lab test . All types of heat pump installations will require a heating distribution pump and all ground sourced installations will also require a collector loop pump i.e. the loop whether contained in a vertical bore or in horizontal trenches has to be pumped to circulate the collector fluid. The electrical consumption demanded of your collector loop pump cannot be accounted for in a lab test .

So for a complete picture one needs to calculate the energy demand of the pump or pumps of the completed installation.

fclauson

one other thing - if using UFH then make sure you sub screed insulation is thick - we have 200mm regs is a lot less - but this will suck out the heat into the ground if you don't put enough in

Condenser

sinnerboy wrote: »

Heat pumps are listed on the SEAI harp database indicating their SPF ( Seasonal Performance Factor ) which is derived from (various ISO accreditated lab tested) COP's for that heat pump.

Here is an example of test data for several Air to Water heat pumps. Notice how when talking about COP one must reference the ambient air temperature and the temperature of the water heated by the heat pump. Not surprisingly the COP improves when the ambient air temperature increases and/or when the temperature of the water heated by the heat pump decreases.

Here are SEAI's rules for arriving at the SPF. Depending on the type of heat pump the tested COP's are adjusted or aggregated into one figure the SPF for use in DEAP.

But to answer the OP query one should seek out the range of COP's as determined by testing according to EN 14511, EN 16147 and EN 255-3:

For further test results look here

TBH those SEAI figures aren't worth a damn and have no real reflection of what a heat pump will return. Your COP/SPF will be determined on site, not in the factory and SEAI's method of deficiting for hot water is crude to say the least. Their methods are based on assumptions and even those don't incorporate best practice.

sinnerboy

Condenser wrote: »

TBH those SEAI figures aren't worth a damn and have no real reflection of what a heat pump will return.

The figures are a treatment of COP's tested to EU Norms in Accredited labs and as such are useful to compare one model against another.

Condenser wrote: »

Your COP/SPF will be determined on site, not in the factory

I believe I made that point already

Condenser wrote: »

and SEAI's method of deficiting for hot water is crude to say the least. Their methods are based on assumptions and even those don't incorporate best practice.

Can you elaborate please?

Condenser

sinnerboy wrote: »

The figures are a treatment of COP's tested to EU Norms in Accredited labs and as such are useful to compare one model against another.



I believe I made that point already



Can you elaborate please?

I was refering to SEAI's figures.

The figures are discounted COP's to allow for hot water production, they automatically drop 20% off the rated COP to compensate. It doesn't depend on system or how your DHW is produced or whether an immersion is employed. They don't even give two distinct COP's, one at 35C condensing and one at 50C condensing. They just give the blunt instrument approach across the board.
You can compare COP's all day but the fact will remain that two different installers will most likely get two different results from the same heat pump is fitted in the same house due to the installation practices employed.