Optimising DHW in summer (once heating season ends)
I'm trying to understand how flow rates affect DHW heating efficiency with a view to optimising flow rates in summer once heating is no longer required.
My system uses fixed rate pumps, so is it more efficient to set a faster or slower flow rate for the DHW cycle?
A slower flow rate presumably allows more time for the heat in the circulating water to transfer into the DHW tank and thus widens the dT between flow and return, which means the final LWT would need to be higher to achieve any given DHW tank set point?
That would suggest a higher flow rate may be more cost effective? But then there's the additional electricity cost of running the circulation pump(s) faster, albeit for a relatively short period of time (my Wilo pumps use ~30Wh more running at max speed versus turning them down by one setting, so maybe 15W over the 30min DHW cycle so probably negligible at a saving of around 1% of the overall electrical usage).
I hate the prospect of leaving a few percentage points of performance on the table for what is an otherwise simple change. Or am I just massively overthinking this and it's going to make no meaningful difference?
Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.
Posted by: @old_scientistI hate the prospect of leaving a few percentage points of performance on the table for what is an otherwise simple change. Or am I just massively overthinking this and it's going to make no meaningful difference?
Unless you use negligible hot water the energy used by the compressor will dominate, the water pump will be negligible. So you should optimise for that. Some ASHPs have more than one option for DGHW (eg an 'eco' setting) which takes longer but uses less juice. Does yours?
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
Posted by: @jamespaPosted by: @old_scientistI hate the prospect of leaving a few percentage points of performance on the table for what is an otherwise simple change. Or am I just massively overthinking this and it's going to make no meaningful difference?
Unless you use negligible hot water the energy used by the compressor will dominate, the water pump will be negligible. So you should optimise for that. Some ASHPs have more than one option for DGHW (eg an 'eco' setting) which takes longer but uses less juice. Does yours?
Yes, I already run in the Samsung equivalent Quiet Mode for DHW, which limits output to around 70% and which is more efficient.
Now I'm looking at the effects of flow rate. I agree the potential electrical savings for different circulation pump speeds is negligible at ~1% of overall electrical input.
Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.
- 26 Forums
- 2,171 Topics
- 47.8 K Posts
- 23 Online
- 5,744 Members
Join Us!
Podcast Picks
Latest Posts
-
RE: Testing new controls/monitoring for Midea Clone ASHP
Thanks, that might explain the when, and possibly the w...
By cathodeRay , 6 minutes ago
-
RE: Big Changes Coming to Our Heat Pump System
We could I'm sure (mine for example, nothing special at...
By JamesPa , 32 minutes ago
-
-
RE: Mitsu PAR-WT60R Wireless Controller - options
How it does it's job is something of a mystery although...
By Abernyte , 2 hours ago
-
RE: MCS certificate SCOP vs real-world performance
MCS:3.65 Reported by Vaillant: 3.96 (heating only); 3....
By JamesPa , 4 hours ago
-
RE: Powerwall 3 or Myenergi or something else?
Yes I was thinking of outdoor, IP65 batteries with buil...
By Temperature_Gradient , 6 hours ago
-
RE: Help me keep the faith with my air source heat pump installation
Water pump will certainly make a hum (which could conce...
By JamesPa , 9 hours ago
-
@jamespa Thanks. Yeah any adjustments Ive made at pr...
By cliffhanger , 9 hours ago
-
RE: How to choose Towel Rails for an ASHP
@rob-nezard yes absolutely. Here is the link and a pho...
By GrahamF , 2 days ago
-
@mixergy Thanks for the update, I would appreciate some...
By bontwoody , 2 days ago
-
RE: Is Your Broadband Router the Weak Link in Your High-Tech Home?
Unfortunately I'm not that well connected 😂 ...
By Scalextrix , 2 days ago
-
RE: A Customer's Lessons Learnt from a Heat Pump Installation in a Large House
It is interesting to see what our new Grant Aerona 290 ...
By GrahamF , 2 days ago
-
RE: Midea ASHP – how to set weather compensation
I noticed that too and thought the same thing, but then...
By cathodeRay , 3 days ago
-
RE: Ya can’t win! It is S*d’s Law!
@old_scientist If IOF is still running next late spring...
By Toodles , 3 days ago
-
RE: Electricity price predictions
Those of you on Agile will do well tomorrow; there are ...
By Toodles , 3 days ago
-
RE: Who’s Caved and Switched the Heating On Already?
We've been running our Ecodan system, installed in June...
By Sheriff Fatman , 3 days ago
-
Ok. Two schools of thought. The first is to run the ...
By JamesPa , 4 days ago
-
@drei Willing as I am to help, I don't think I'm yet ...
By JamesPa , 4 days ago
-
Selling 5 year old ASHP & Gas Combi Boiler - £590
Selling a 5-year-old Daikin Altherma Hybrid Air Source ...
By Paul G , 4 days ago