Interesting SCOP with an MVHR

anon_ymous

I came across this website : 

https://heatpumpmonitor.org/

The person with the highest SCOP has an MVHR. Granted, they haven't had it for long but an average SCOP of 6.7 is pretty damn good

I'll be looking at that over the winter to gauge what might be possible. Though getting a COP 6.4 even for the past month is pretty good

I imagine the MVHR is helping a lot with their setup. 

DougMLancs

The main reason their performance is so high is that they’re running at 31C flow temp with weather compensation, no buffer, no zoning on trv’s (just overheat protection and no glycol. 

Part of the reason that they can run such a low flow temp through their radiators is that it looks like they’ve calculated the MVHR to cover around 1400kWh of the 6345kWh heat loss based on the heat pump size being 5kW. In theory though, they could’ve skipped the MVHR and gone for a larger emitter area to have the same COP so you don’t HAVE to have MVHR to get such figures.

In our case, 8 K2’s and 1 K3 with decentralised MVHR in the kitchen and bathroom was enough for us to design to a flow temperature of 35C. Yes we could’ve gone all out with extra wall insulation and super efficient glazing first but the benefit isn’t proportional to the cost so we’ll save that for when the opportunity naturally presents itself (and there are no toddlers around!).

anon_ymous

DougMLancs said:

The main reason their performance is so high is that they’re running at 31C flow temp with weather compensation, no buffer, no zoning on trv’s (just overheat protection and no glycol. 

Part of the reason that they can run such a low flow temp through their radiators is that it looks like they’ve calculated the MVHR to cover around 1400kWh of the 6345kWh heat loss based on the heat pump size being 5kW. In theory though, they could’ve skipped the MVHR and gone for a larger emitter area to have the same COP so you don’t HAVE to have MVHR to get such figures.

In our case, 8 K2’s and 1 K3 with decentralised MVHR in the kitchen and bathroom was enough for us to design to a flow temperature of 35C. Yes we could’ve gone all out with extra wall insulation and super efficient glazing first but the benefit isn’t proportional to the cost so we’ll save that for when the opportunity naturally presents itself (and there are no toddlers around!).

How do you know they've calculated the MVHR to cover 1400 kWh? Is it due to the heat pump only being a 5 kW unit? 

anon_ymous

DougMLancs said:

The main reason their performance is so high is that they’re running at 31C flow temp with weather compensation, no buffer, no zoning on trv’s (just overheat protection and no glycol. 

Part of the reason that they can run such a low flow temp through their radiators is that it looks like they’ve calculated the MVHR to cover around 1400kWh of the 6345kWh heat loss based on the heat pump size being 5kW. In theory though, they could’ve skipped the MVHR and gone for a larger emitter area to have the same COP so you don’t HAVE to have MVHR to get such figures.

In our case, 8 K2’s and 1 K3 with decentralised MVHR in the kitchen and bathroom was enough for us to design to a flow temperature of 35C. Yes we could’ve gone all out with extra wall insulation and super efficient glazing first but the benefit isn’t proportional to the cost so we’ll save that for when the opportunity naturally presents itself (and there are no toddlers around!).

Also, may I askwhat's a K2 and K3? 

DougMLancs

waqasahmed said:

How do you know they've calculated the MVHR to cover 1400 kWh? Is it due to the heat pump only being a 5 kW unit? 

That’s the assumption I’ve made, the installer could also have not designed the system for the 5% of the heating season when it’s as cold as the design temperature in the heat loss calculation. Instead, just sizing it for the majority of the heating load and the owner puts their log burner on if needed?

DougMLancs

Sorry they’re radiator types- a K2 has two panels and two sets of fins (also called a type 22). A K3 (type 33) is a proper beast and has 3 panels and 3 sets of fins.

anon_ymous

DougMLancs said:

The main reason their performance is so high is that they’re running at 31C flow temp with weather compensation, no buffer, no zoning on trv’s (just overheat protection and no glycol. 

Part of the reason that they can run such a low flow temp through their radiators is that it looks like they’ve calculated the MVHR to cover around 1400kWh of the 6345kWh heat loss based on the heat pump size being 5kW. In theory though, they could’ve skipped the MVHR and gone for a larger emitter area to have the same COP so you don’t HAVE to have MVHR to get such figures.

In our case, 8 K2’s and 1 K3 with decentralised MVHR in the kitchen and bathroom was enough for us to design to a flow temperature of 35C. Yes we could’ve gone all out with extra wall insulation and super efficient glazing first but the benefit isn’t proportional to the cost so we’ll save that for when the opportunity naturally presents itself (and there are no toddlers around!).

Could I also ask why you wouldn't use glycol? I thought it's useful as an anti freeze? 

shinytop

waqasahmed said:

DougMLancs said:

The main reason their performance is so high is that they’re running at 31C flow temp with weather compensation, no buffer, no zoning on trv’s (just overheat protection and no glycol. 

Part of the reason that they can run such a low flow temp through their radiators is that it looks like they’ve calculated the MVHR to cover around 1400kWh of the 6345kWh heat loss based on the heat pump size being 5kW. In theory though, they could’ve skipped the MVHR and gone for a larger emitter area to have the same COP so you don’t HAVE to have MVHR to get such figures.

In our case, 8 K2’s and 1 K3 with decentralised MVHR in the kitchen and bathroom was enough for us to design to a flow temperature of 35C. Yes we could’ve gone all out with extra wall insulation and super efficient glazing first but the benefit isn’t proportional to the cost so we’ll save that for when the opportunity naturally presents itself (and there are no toddlers around!).

Could I also ask why you wouldn't use glycol? I thought it's useful as an anti freeze? 

A typical glycol mix for an ASHP increases by c. 5% the amount of liquid that needs to be pumped round the system, because it has a lower heat capacity than pure water.  It's also more viscous than water so the circulation pumps have to work harder.  And, it's expensive; maybe £200 to treat an ASHP system.  It's not the same very toxic stuff you put in your car that is cheap as chips. But as well as freeze protection, it contains additional things like corrosion and bacterial inhibitors. 

You can fit antifreeze valves instead but if they freeze or stick; they will empty all the water out of the system.  

Or you can use nothing and hope you don't have an extended power cut when it's very cold. 

anon_ymous

shinytop said:

waqasahmed said:

DougMLancs said:

The main reason their performance is so high is that they’re running at 31C flow temp with weather compensation, no buffer, no zoning on trv’s (just overheat protection and no glycol. 

Part of the reason that they can run such a low flow temp through their radiators is that it looks like they’ve calculated the MVHR to cover around 1400kWh of the 6345kWh heat loss based on the heat pump size being 5kW. In theory though, they could’ve skipped the MVHR and gone for a larger emitter area to have the same COP so you don’t HAVE to have MVHR to get such figures.

In our case, 8 K2’s and 1 K3 with decentralised MVHR in the kitchen and bathroom was enough for us to design to a flow temperature of 35C. Yes we could’ve gone all out with extra wall insulation and super efficient glazing first but the benefit isn’t proportional to the cost so we’ll save that for when the opportunity naturally presents itself (and there are no toddlers around!).

Could I also ask why you wouldn't use glycol? I thought it's useful as an anti freeze? 

A typical glycol mix for an ASHP increases by c. 5% the amount of liquid that needs to be pumped round the system, because it has a lower heat capacity than pure water.  It's also more viscous than water so the circulation pumps have to work harder.  And, it's expensive; maybe £200 to treat an ASHP system.  It's not the same very toxic stuff you put in your car that is cheap as chips. But as well as freeze protection, it contains additional things like corrosion and bacterial inhibitors. 

You can fit antifreeze valves instead but if they freeze or stick; they will empty all the water out of the system.  

Or you can use nothing and hope you don't have an extended power cut when it's very cold. 

Thanks. Surely it's still better to have glycol than not? Ie: for the protection of the system?

I mean I wouldn't turn my radiators completely off in winter for example, purely because the pipes would potentially crack if they don't have heat going through them 

Qyburn

waqasahmed said:

I came across this website : 

https://heatpumpmonitor.org/

The person with the highest SCOP has an MVHR. Granted, they haven't had it for long but an average SCOP of 6.7 is pretty damn good

I see right now it's showing a COP of over 8, with flow temp of 27 Deg C. But it doesn't explain why they need heat at all , so another way of looking at it would be they're using 650W more for heat than we are.  

Presumably the MVHR recovered energy doesn't actually enter into the COP calculation, or does it?

shinytop

waqasahmed said:

shinytop said:

waqasahmed said:

DougMLancs said:

The main reason their performance is so high is that they’re running at 31C flow temp with weather compensation, no buffer, no zoning on trv’s (just overheat protection and no glycol. 

Part of the reason that they can run such a low flow temp through their radiators is that it looks like they’ve calculated the MVHR to cover around 1400kWh of the 6345kWh heat loss based on the heat pump size being 5kW. In theory though, they could’ve skipped the MVHR and gone for a larger emitter area to have the same COP so you don’t HAVE to have MVHR to get such figures.

In our case, 8 K2’s and 1 K3 with decentralised MVHR in the kitchen and bathroom was enough for us to design to a flow temperature of 35C. Yes we could’ve gone all out with extra wall insulation and super efficient glazing first but the benefit isn’t proportional to the cost so we’ll save that for when the opportunity naturally presents itself (and there are no toddlers around!).

Could I also ask why you wouldn't use glycol? I thought it's useful as an anti freeze? 

A typical glycol mix for an ASHP increases by c. 5% the amount of liquid that needs to be pumped round the system, because it has a lower heat capacity than pure water.  It's also more viscous than water so the circulation pumps have to work harder.  And, it's expensive; maybe £200 to treat an ASHP system.  It's not the same very toxic stuff you put in your car that is cheap as chips. But as well as freeze protection, it contains additional things like corrosion and bacterial inhibitors. 

You can fit antifreeze valves instead but if they freeze or stick; they will empty all the water out of the system.  

Or you can use nothing and hope you don't have an extended power cut when it's very cold. 

Thanks. Surely it's still better to have glycol than not? Ie: for the protection of the system?

I mean I wouldn't turn my radiators completely off in winter for example, purely because the pipes would potentially crack if they don't have heat going through them 

I think you'd be unwise to have no antifreeze protection at all.  Most people have their heating on in winter or if on holiday they leave it on a holiday setting, which keeps it ticking over.  Problems could occur if there is a power cut for say 24 hours or more and it's very cold. 

I have glycol in mine because it's what the installers use as standard because the manufacturer (Mitsubishi) recommends it.  If it's a little less efficient then so be it.