In general - are shorter hotter cycles more costly or longer cooler cycles?
I'm trying to get to a balance with my system. I'm starting a new topic as this is quite specific.
Essentially with my system a downstairs zone doesn't perform as well as others due to very short in frequent cycles. Unless I keep upstairs zone open, cycles are more frequent/longer, but then the challenge with that is upstairs overheats/I have to really balance down upstairs which is proving complicated due to different use cases on the first floor (unless I crash down TRVs in bedrooms, bedrooms overheat etc etc).
What I'm finding is that upping the minimum flow temp on the ASHP, lets downstairs get more to temp with these very infrequent cycles (and they seem to be at the moment maybe 4x-6x a day - outdoors ranges from 10-12C here atm).
What I'd like to ascertain is, in theory what would be cheaper to run:
- more frequent cycles at a lower temp, but a zone heated that doesn't need it
- far less frequent cycles at a higher temp, with just the problem zone calling for heat
Difference so far is option 1 with a min temp of 29C, gets to around 19.5-21C (rooms performing differently).
Option 2 is seems to push towards 21C, but the min temp is 32C, so there's a 3C difference in min temp with the WC atm it's a 2C flow temp difference. Min temp is set to run when outdoors is 20C. However am seeing the rooms are closer performing downstairs.
Ideal situation would be to rip apart the plant room and optimise the actual temp hitting rads but currently not an option.
In purely theoretical terms the cooler the flow temperature the more efficient the heat pump is at delivering any given amount of energy, so longer and cooler is better than shorter and hotter - this is a function of the basic thermodynamics (the Carnot equation/cycle if you want to research it)
However your flow temperatures are low, so the thermodynamic efficiency difference may be 2% or less per degree C increase in flow temperature. You are suggesting only a modest increase of 3C and its quite likely that the thermodynamic difference, particularly at moderate outdoor temperatures, will be dominated by engineering factors. I think you are going to need to experiment, although it may be difficult to make an accurate determination because you cant control the key variables!
I know that's not very helpful but even with quite long setbacks of several hours its proving difficult to reconcile experimental results (with all their problems) with simple (albeit robust) theory. Particularly at moderate temperatures the 'engineering' factors, which are difficult to take into account/aren't actually declared by the manufacturers, seem to have a material influence.
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.
Thanks James. I'll keep experimenting. I suspect a spreadsheet that supplements the WC reckoner someone made (apologies every time forget who it was, and it's specific to the Grant ASHP), I'll have to note which temps at ambient temps get me to desired room temps depending on running upstairs along side or not.
Probably a long haul.
Next year I think I'll finally give in to allowing EON to install a smart meter and map against running costs also.
Posted by: @crimsonThanks James. I'll keep experimenting. I suspect a spreadsheet that supplements the WC reckoner someone made (apologies every time forget who it was, and it's specific to the Grant ASHP), I'll have to note which temps at ambient temps get me to desired room temps depending on running upstairs along side or not.
Probably a long haul.
Next year I think I'll finally give in to allowing EON to install a smart meter and map against running costs also.
Good idea. You will probably find that the cycling 'problem' disappears as it gets cooler. Its probably best not to get too intense about this, you could probably drive yourself mad! Think of it as a slow long walk not a sprint or marathon.
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.
- 22 Forums
- 2,005 Topics
- 43.8 K Posts
- 7 Online
- 3,166 Members
Join Us!
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: Is my Samsung heat pump working too well?
You have had good advice so far, but I am just wonderin...
By guthrie , 5 hours ago
-
Yes there is, provided the buffer is tall and well desi...
By JamesPa , 6 hours ago
-
RE: Grant Aerona fine tuning advice needed
I have a Aerona3 13kW and my current settings are max F...
By Grantmethestrength , 6 hours ago
-
RE: Solar Power Output – Let’s Compare Generation Figures
Our March generation was 133% of our PVGIS prediction a...
By Old_Scientist , 8 hours ago
-
RE: Setback savings - fact or fiction?
I'm not a statistician, but I have had to use statistic...
By cathodeRay , 9 hours ago
-
@jamespa thanks. I will take some time to make a head-t...
By Eliuccio , 13 hours ago
-
RE: Are Homeowners Being Silenced Over Faulty Heat Pumps?
Spot on. Last month, a homeowner booked a consultation ...
By Mars , 1 day ago
-
RE: Who's your electricity provider and what's your tariff?
@matthew_w It's a complex area and every case is diff...
By JamesPa , 1 day ago
-
RE: Multiple simultaneous connections to Samsung R290 heat pump via Modbus
Thanks for the various replies. I've tried to summari...
By Angus , 1 day ago
-
RE: Help me keep the faith with my installation
@adamk Yes, it's a good way and an alternative to (o...
By JamesPa , 2 days ago
-
RE: Frequent power outages in the Southeast – A sign of things to come?
That's a useful observation @majordennisbloodnok I'd ...
By Transparent , 2 days ago
-
RE: NIBE F2040 12 kW heat pump and 100 liter buffer tank
Glad to hear that things are moving forward. The photo...
By JamesPa , 2 days ago
-
RE: Jokes and fun posts about heat pumps and renewables
@judith Our peak is 5.4 kWp today and so far (16:35) we...
By Toodles , 3 days ago
-
RE: Forum updates, announcements & issues
@transparent I rather think that your LPA might refussi...
By Toodles , 3 days ago
-
RE: Baxi Air Source Heat Pump tips and tricks
Nah, tiz them Cornish coliflour 'eads goin to announce ...
By Broadsman , 3 days ago
-
RE: Should I insulate the flow and return on my rad circuit?
red is 28mm orange is 22mm.
By AdamK , 3 days ago
-
-
RE: New Heat Pump - mixer shower pressure
Just note that this will yield a reduction in pressure ...
By Transparent , 3 days ago
-
RE: Renewable Heating Hub Partners with Heat Geek
@mars as a matter of interest have you got any near Sta...
By JamesPa , 3 days ago
Most Active This Week
# | Name | kWhs |
---|---|---|
1 | Mars | 324 |
2 | JamesPa | 114 |
3 | Majordennisbloodnok | 99 |
4 | Transparent | 79 |
5 | cathodeRay | 66 |
6 | Tim441 | 65 |
7 | Toodles | 60 |
8 | Heatgeek | 53 |
9 | Pooneil | 48 |
10 | Potatoman | 43 |