Notifications

Clear all

Joining the Renewable Heating Hub forums is completely free and only takes a minute. By registering you’ll be able to ask questions, join discussions, follow topics you’re interested in, bookmark useful threads and receive notifications when someone replies. Non-registered members also do not have access to our AI features. When choosing your username, please note that it cannot be changed later, so we recommend avoiding brand or product names. Before registering, please take a moment to read the Forum Rules & Terms of Use so we can keep the community helpful, respectful and informative for everyone. Thanks for joining!

Significance of delta betweeen flow and return temperature

Air Source Heat Pumps (ASHPs)

Last Post by HydroS 4 years ago

11 Posts

4 Users

4 Reactions

2,314 Views

RSS

greekgoddj

(@greekgoddj)

Eminent Member Member

Joined: 4 years ago

Posts: 20

Topic starter 23/01/2022 3:01 pm [#287]

Hi everyone,

I have been wondering about the following. Does the delta between the flow and return temperature have an impact on the efficiency/energy use of the ASHP? For example, assuming a ASHP that is focused on heating the flow to 40C, does it matter if what returns is 20C or 30C? In other words, if it is heating 1 room or 5 rooms, as long as the ASHP is aiming for a certain flow temperature (whether said temperature is manually set or driven by compensation curve), is the workload on the ASHP the same?

Thanks

Mitsubishi Ecodan 11.2kW ASHP

Quote

Derek M

(@derek-m)

Illustrious Member Member

Joined: 5 years ago

Posts: 4425

23/01/2022 5:11 pm

Posted by: @greekgoddj

Hi everyone,

I have been wondering about the following. Does the delta between the flow and return temperature have an impact on the efficiency/energy use of the ASHP? For example, assuming a ASHP that is focused on heating the flow to 40C, does it matter if what returns is 20C or 30C? In other words, if it is heating 1 room or 5 rooms, as long as the ASHP is aiming for a certain flow temperature (whether said temperature is manually set or driven by compensation curve), is the workload on the ASHP the same?

Thanks

Hi,

The simple answer is yes, the delta T of the flow and return water does impact the efficiency and energy use of a heat pump.

It takes a defined amount of energy to heat a specified amount of water by 1C. So if the water is entering the heat pump at 20C and exiting at 40C, then it will have required 4 times more energy to heat the water than if it was entering at 35C and exiting at 40C.

👍

ReplyQuote

greekgoddj

(@greekgoddj)

Eminent Member Member

Joined: 4 years ago

Posts: 20

Topic starter 23/01/2022 7:48 pm

@derek-m Thanks!

Mitsubishi Ecodan 11.2kW ASHP

ReplyQuote

HydroS

(@hydros)

Estimable Member Member

Joined: 4 years ago

Posts: 59

03/03/2022 11:37 pm

Picking up this significance of deltaT topic again but from the opposite side.

My system is an Daikin Altherma 11kw Monobloc, described in other threads. I have it working with weather comp, with the internal controller modulating the leaving water temperature. It's working alright, COP about 3.2, but I notice after the overnight setback, the pump runs nicely with a deltaT around 5C, and if I record the meters (fitted as part of a trial) the COP for this period is up above 3.6, but as the house reaches temperature a bit of modulation happens reducing the leaving water temperature gradually, but then leaving and return water temperatures end up being very similar, often the same for several hours, so no deltaT. The house is warm enough, so there is no heat demand in the property but the pump keeps running in this tick over state, and this drops the COP drastically because the ASHP is using electricity but not putting heat in to the property. So that's the scenario. Should I be trying to achieve a greater deltaT through the radiators? I could wind in the locksheilds on my rads, whilst keeping the system balanced, to reduce flow and allow a greater temperature drop across them? This is counter intuitive though as I've read that high flow rates are better for heat pumps.

Thoughts appreciated about whether I'm over thinking this one.

ReplyQuote

adaml

(@adaml)

Eminent Member Member

Joined: 4 years ago

Posts: 42

04/03/2022 2:57 pm

@hydros I see similar behaviour with my Daikin with rads as well, COP for Feb was 3.6. I wonder what value you are using for Leaving Water Temperature Maximum Modulation? What weather dependent heat curve are you using?

ReplyQuote

HydroS

(@hydros)

Estimable Member Member

Joined: 4 years ago

Posts: 59

04/03/2022 5:07 pm

@adaml I don’t have the option to set a maximum modulation value, for some reason that menu option doesn’t show. It’s the 11kw Altherma monobloc, the last gen, not the latest one.
The curve is 44C/-5 and 23C/15

ReplyQuote

adaml

(@adaml)

Eminent Member Member

Joined: 4 years ago

Posts: 42

04/03/2022 5:56 pm

@hydros Are you comfortable accessing Installer settings > Overview field settings?

ReplyQuote

HydroS

(@hydros)

Estimable Member Member

Joined: 4 years ago

Posts: 59

04/03/2022 5:58 pm

@adaml yes.
I’ve had to learn because the installer didn’t know what he was doing…

ReplyQuote

adaml

(@adaml)

Eminent Member Member

Joined: 4 years ago

Posts: 42

04/03/2022 6:26 pm

@hydros

What value do you have for [8-06]?

ReplyQuote

HydroS

(@hydros)

Estimable Member Member

Joined: 4 years ago

Posts: 59

04/03/2022 6:49 pm

@adaml I don’t know how to get to that value. It’s not in a menu option. Is it only available via laptop access? The installer manual has this

ReplyQuote

HydroS

(@hydros)

Estimable Member Member

Joined: 4 years ago

Posts: 59

07/03/2022 7:57 pm

@adaml I worked it, I scrolled through the overview settings, I’d left this lot alone until now.
8-06 looks to be 3. Have I read that correctly? Is that a sensible number? I’m guessing it’s not enough. Today with the solar gain the house is up at nearly 23C, with the LWT at around 30C.