Significance of delta betweeen flow and return temperature
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
Posted by: @greekgoddjHi 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.
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.
@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
@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.
- 22 Forums
- 2,096 Topics
- 46.1 K Posts
- 153 Online
- 3,383 Members
Trusted Installers
Struggling to find a reliable heat pump installer? A poor installation can lead to inefficiencies and high running costs. We now connect homeowners with top-rated installers who deliver quality work and excellent service.
✅ Verified, trusted & experienced installers
✅ Nationwide coverage expanding
✅ Special offers available
Latest Posts
-
RE: Mitsubishi cycling while on chilled water output
@iaack they have a finned emitter at the bottom a bit l...
By downfield , 41 minutes ago
-
@jamespa Thanks for the advice - very helpful. I had al...
By abam48 , 7 hours ago
-
RE: Weather compensated secondary circuits with Biomass
Hi @andycoo we do an LK 110 standalone weather compensa...
By Sune , 7 hours ago
-
RE: Adding battery storage to SolarEdge PV system
@chandykris No need to apologise at all! I forgot to ad...
By Toodles , 1 day ago
-
RE: Say hello and introduce yourself
Yes please do Suggesting a loss in the region...
By JamesPa , 1 day ago
-
RE: Surface mount or bury primaries for heat pump installation?
Can we have some links to those you're considering plea...
By Transparent , 1 day ago
-
RE: Commencing on an ASHP Installation Process
That outside pipework would concern me. Surely rigid se...
By benson , 2 days ago
-
As I have reported elsewhere we turned on the cooling o...
By downfield , 2 days ago
-
-
@el3b Hi, sorry to hear that, it is advisable to instal...
By ASHP-BOBBA , 3 days ago
-
RE: Difficult positioning of air source heat pump
@rikiarn Out of intrigue, the thread reads as though Ai...
By Sheriff Fatman , 3 days ago
-
RE: Mitsubishi Ecodan Fails to Heat Water despite temperature drop
@m1kegibson If you are able to access the service me...
By HarriUp , 3 days ago
-
RE: When will heat pumps and install prices come down?
... which of course is impossible because the world mov...
By JamesPa , 3 days ago
-
RE: Battery storage to run Heat Pump.
I would be surprised if the battery chemistry is going ...
By Transparent , 4 days ago