Tweaking ASHP for best efficiency?
Discussion
Mitsubishi Ecodan R32 6kW heat pump installed a week ago, along with an extra radiator in each of the 2 main living areas - existing rads a bit marginal. Looks like the second bedroom and my worksop (3rd bedroom) will need bigger rads, as they struggle to get up to temperature, while the rest of the house is fine at the lowest outside temperature we've had so far - around 4 degrees.
All rooms are fine today, outside temp is 13 degrees.
Upgrading the rads will wait until the spring, as it may be necessary to do more if it gets really cold. Much easier to drain once, and do all the work in one go.
I'm on Octopus Go, so cheap rate between 00:30 and 05:30. Water heating is set for an hour from 00:30, then the heating runs with no setback until 05:30 (making maximum use of the cheap rate).
Setback periods are 05:30 to 07:30, and 20:30 until until the cheap rate kicks in again.
Setback is 4 degrees lower than the normal temps. I work from home.
The system was installed using some basic weather comp settings that "we know to be a good starting point for this area and type of property".
Currently set for 50 degree flow at zero outside, 40 degree flow at 14 outside, and a 3rd setting of 49 degree flow at 1 outside.
I'm in West Cornwall, so it rarely drops below freezing.
Seems to me that the minimum flow temp might be a bit high?
Maybe I should lower it a bit from 40 degrees, but should I also adjust the outdoor temp that it starts ramping up the flow temp?
What does the third setting ( currently 49 degrees flow at 1 outside) actually do? Is it a "turnover/tilt" point for the curve?
I'm a bit stuck on seeing how tweaking settings alters COP, as I can only see cumulative monthly readings for input and output energy - no daily or instant figures.
I can see flow and return temps as a daily or weekly graph. The flow temp does go up and down, reflecting the outside temp. Flow and return also maintain a reasonably stable delta of around 3 degrees.
Running costs are averaging under £3 a day, average 16.5kWH extra consumption per day.
Averaged over the 8 days since installation, COP is 2.95.
More expensive than the old oil boiler, but the whole house is now comfortable, rather than just a couple of rooms.
Just looking to see if I can save a bit by tweaking.
All rooms are fine today, outside temp is 13 degrees.
Upgrading the rads will wait until the spring, as it may be necessary to do more if it gets really cold. Much easier to drain once, and do all the work in one go.
I'm on Octopus Go, so cheap rate between 00:30 and 05:30. Water heating is set for an hour from 00:30, then the heating runs with no setback until 05:30 (making maximum use of the cheap rate).
Setback periods are 05:30 to 07:30, and 20:30 until until the cheap rate kicks in again.
Setback is 4 degrees lower than the normal temps. I work from home.
The system was installed using some basic weather comp settings that "we know to be a good starting point for this area and type of property".
Currently set for 50 degree flow at zero outside, 40 degree flow at 14 outside, and a 3rd setting of 49 degree flow at 1 outside.
I'm in West Cornwall, so it rarely drops below freezing.
Seems to me that the minimum flow temp might be a bit high?
Maybe I should lower it a bit from 40 degrees, but should I also adjust the outdoor temp that it starts ramping up the flow temp?
What does the third setting ( currently 49 degrees flow at 1 outside) actually do? Is it a "turnover/tilt" point for the curve?
I'm a bit stuck on seeing how tweaking settings alters COP, as I can only see cumulative monthly readings for input and output energy - no daily or instant figures.
I can see flow and return temps as a daily or weekly graph. The flow temp does go up and down, reflecting the outside temp. Flow and return also maintain a reasonably stable delta of around 3 degrees.
Running costs are averaging under £3 a day, average 16.5kWH extra consumption per day.
Averaged over the 8 days since installation, COP is 2.95.
More expensive than the old oil boiler, but the whole house is now comfortable, rather than just a couple of rooms.
Just looking to see if I can save a bit by tweaking.
With my boiler, you can set the weather comp 'linear' so flow temp graphed against outdoor temp is a straight line, or you can put a curve in that graph by specifying more points.
Your third point is so close to one of the end points, I can't see it doing much unless there is some quirk in the software.
Can you not get a bunch of graphs for your heat pump? COP vs flow temp for various ambient?
If you're using cheap rate power, then you'll probably find that chasing best COP needs to be secondary to making the most of cheap rate?
Your rooms with small rads may be more efficient if they are kept up to temp 24/7? Or even overheated a little during cheap rate?
Can you program the flow temp to be different during cheap and peak rates?
Your third point is so close to one of the end points, I can't see it doing much unless there is some quirk in the software.
Can you not get a bunch of graphs for your heat pump? COP vs flow temp for various ambient?
If you're using cheap rate power, then you'll probably find that chasing best COP needs to be secondary to making the most of cheap rate?
Your rooms with small rads may be more efficient if they are kept up to temp 24/7? Or even overheated a little during cheap rate?
Can you program the flow temp to be different during cheap and peak rates?
OutInTheShed said:
With my boiler, you can set the weather comp 'linear' so flow temp graphed against outdoor temp is a straight line, or you can put a curve in that graph by specifying more points.
Your third point is so close to one of the end points, I can't see it doing much unless there is some quirk in the software.
Can you not get a bunch of graphs for your heat pump? COP vs flow temp for various ambient?
If you're using cheap rate power, then you'll probably find that chasing best COP needs to be secondary to making the most of cheap rate?
Your rooms with small rads may be more efficient if they are kept up to temp 24/7? Or even overheated a little during cheap rate?
Can you program the flow temp to be different during cheap and peak rates?
I've just tried tweaking the third compensation curve setting, and it does indeed add an extra point along the curve (straight line in reality), pulling the curve up/down like an elastic band between the fixed points defined by the first two settings. Probably a bit pointless in UK weather? I guess that's why the videos I've watched gloss over it's function.Your third point is so close to one of the end points, I can't see it doing much unless there is some quirk in the software.
Can you not get a bunch of graphs for your heat pump? COP vs flow temp for various ambient?
If you're using cheap rate power, then you'll probably find that chasing best COP needs to be secondary to making the most of cheap rate?
Your rooms with small rads may be more efficient if they are kept up to temp 24/7? Or even overheated a little during cheap rate?
Can you program the flow temp to be different during cheap and peak rates?
The only efficiency info I can find states COP of 3.2 (at -7 degrees outside temp, flow temp 35 degrees, return temps 30 degrees), and SCOP of 3.3 at 55 degrees, SCOP 4.62 at 35 degrees.
Yes, COP is going to be less important than maximising use during the off peak period.
I guess the COP I'm getting is a bit less than the quoted figure because the heat pump is "cycling" when the rooms get up to temperature, and going off during the setback periods.
A balancing act between efficiency, energy consumption, and actual cost with a dual-rate tariff.
I can't see a way of altering the flow temp during off peak periods.
The lack of data coming from the unit seems to be a common complaint on various forums. Maybe that's the Japanese " we built it, we know best, so leave it alone" mentality?
Tweaking settings without data to compare each time is going to be tricky. Difficult to compare when the outside temperature varies so much.
Edited to add:
To put it into context, when we had no heating during the installation, we were using a fan heater and oil-filled radiator to take the chill off in the hallway and bathroom, anvoil-filled radiator to keep the kitchen/diner at 20 degrees, and the livingroom stove for 3 hours in the evening. That lot was using over a fiver of extra electricity, and £3 of logs, each day. Much of the house was only a couple of degrees above ambient - a bit nippy.
By comparison, the ASHP is proving pretty economical to run, lol.
Edited by clockworks on Saturday 21st December 16:49
The changes in cop are fairly linear with changes in flow temp, so if you have cop at the same ambient and 2 different flow temperatures you can extrapolate, there is a rule of thumb in refrigeration that for every 1 deg c you reduce condensing temperature (you could assume the same for every 1deg you reduce flow temperature) efficiency improves by 2-4%, in most cases it’s closer to 2%.
A 6kW heat pump is not very big, I suspect there will be times it won't keep up - but that's beside the point.
Far to often a heat pump is compared to a boiler, when in fact they are fundamentally different.
In my opinion, trying to use "weather compensation" or setting "output temperatures" with a heat pump will by definition lower the efficiency.
Put it another way, a 6kW heat pump can produce 6kW of energy - conventional boiler thinking is that to make a house warmer you need a higher flow temperature - if you do this with a heat pump, the efficiency or COP go down.
If you have 30 litres a minute of water flow, a 6kW heat pump will give a 3 degree temperature rise, ie if water going in to the heat pump is 35 degrees, it will come out at 38. Restricting the flow to give 50 degrees out (from 35 in), will NOT make the house warmer, it WILL lower efficiency and cost more to run.
The closer the input and output temperatures of a heat pump are, the lower the running cost.
Get rid of set output temperatures and maximise flow to give the lowest running cost.
The problem with some heat pump manufacturers is they have set out to show how clever they are, and to give "customers" the impression they are in control. When in fact it is all about water flow.
Getting the temperature rise through the heat pump below 5 degrees (ideally 2 or 3) is the best thing you can do.
caziques said:
A 6kW heat pump is not very big, I suspect there will be times it won't keep up - but that's beside the point.
Far to often a heat pump is compared to a boiler, when in fact they are fundamentally different.
In my opinion, trying to use "weather compensation" or setting "output temperatures" with a heat pump will by definition lower the efficiency.
Put it another way, a 6kW heat pump can produce 6kW of energy - conventional boiler thinking is that to make a house warmer you need a higher flow temperature - if you do this with a heat pump, the efficiency or COP go down.
If you have 30 litres a minute of water flow, a 6kW heat pump will give a 3 degree temperature rise, ie if water going in to the heat pump is 35 degrees, it will come out at 38. Restricting the flow to give 50 degrees out (from 35 in), will NOT make the house warmer, it WILL lower efficiency and cost more to run.
The closer the input and output temperatures of a heat pump are, the lower the running cost.
Get rid of set output temperatures and maximise flow to give the lowest running cost.
The problem with some heat pump manufacturers is they have set out to show how clever they are, and to give "customers" the impression they are in control. When in fact it is all about water flow.
Getting the temperature rise through the heat pump below 5 degrees (ideally 2 or 3) is the best thing you can do.
System has 2 variable speed pumps and a low-loss header. I can see the flow rate through the heat pump, and the temperature difference on the flow and return, on the control panel and app.Far to often a heat pump is compared to a boiler, when in fact they are fundamentally different.
In my opinion, trying to use "weather compensation" or setting "output temperatures" with a heat pump will by definition lower the efficiency.
Put it another way, a 6kW heat pump can produce 6kW of energy - conventional boiler thinking is that to make a house warmer you need a higher flow temperature - if you do this with a heat pump, the efficiency or COP go down.
If you have 30 litres a minute of water flow, a 6kW heat pump will give a 3 degree temperature rise, ie if water going in to the heat pump is 35 degrees, it will come out at 38. Restricting the flow to give 50 degrees out (from 35 in), will NOT make the house warmer, it WILL lower efficiency and cost more to run.
The closer the input and output temperatures of a heat pump are, the lower the running cost.
Get rid of set output temperatures and maximise flow to give the lowest running cost.
The problem with some heat pump manufacturers is they have set out to show how clever they are, and to give "customers" the impression they are in control. When in fact it is all about water flow.
Getting the temperature rise through the heat pump below 5 degrees (ideally 2 or 3) is the best thing you can do.
I can also monitor each radiator for temp drop with a dual-probe meter.
Presumably I can adjust the first pump's speed to get the flow and delta on the heatpump, then use the secondary pump to get the right sort of delta on the rads?
caziques said:
A 6kW heat pump is not very big, I suspect there will be times it won't keep up - but that's beside the point.
Far to often a heat pump is compared to a boiler, when in fact they are fundamentally different.
In my opinion, trying to use "weather compensation" or setting "output temperatures" with a heat pump will by definition lower the efficiency.
Put it another way, a 6kW heat pump can produce 6kW of energy - conventional boiler thinking is that to make a house warmer you need a higher flow temperature - if you do this with a heat pump, the efficiency or COP go down.
If you have 30 litres a minute of water flow, a 6kW heat pump will give a 3 degree temperature rise, ie if water going in to the heat pump is 35 degrees, it will come out at 38. Restricting the flow to give 50 degrees out (from 35 in), will NOT make the house warmer, it WILL lower efficiency and cost more to run.
The closer the input and output temperatures of a heat pump are, the lower the running cost.
Get rid of set output temperatures and maximise flow to give the lowest running cost.
The problem with some heat pump manufacturers is they have set out to show how clever they are, and to give "customers" the impression they are in control. When in fact it is all about water flow.
Getting the temperature rise through the heat pump below 5 degrees (ideally 2 or 3) is the best thing you can do.
That seems right, but in the limit of radiators being on the small side, the radiator needs to reach certain temp to match the heat loss of the room.Far to often a heat pump is compared to a boiler, when in fact they are fundamentally different.
In my opinion, trying to use "weather compensation" or setting "output temperatures" with a heat pump will by definition lower the efficiency.
Put it another way, a 6kW heat pump can produce 6kW of energy - conventional boiler thinking is that to make a house warmer you need a higher flow temperature - if you do this with a heat pump, the efficiency or COP go down.
If you have 30 litres a minute of water flow, a 6kW heat pump will give a 3 degree temperature rise, ie if water going in to the heat pump is 35 degrees, it will come out at 38. Restricting the flow to give 50 degrees out (from 35 in), will NOT make the house warmer, it WILL lower efficiency and cost more to run.
The closer the input and output temperatures of a heat pump are, the lower the running cost.
Get rid of set output temperatures and maximise flow to give the lowest running cost.
The problem with some heat pump manufacturers is they have set out to show how clever they are, and to give "customers" the impression they are in control. When in fact it is all about water flow.
Getting the temperature rise through the heat pump below 5 degrees (ideally 2 or 3) is the best thing you can do.
If you want a room to get from say 18 to 20 in e.g. an hour, you need to raise the flow temp again.
The flow temp will need to be set for the room with the most undersized rad.
Having the rooms with small rads a bit cooler, but constant 24/7 might enable the whole system to run at a lower flow temp.
But there may be a balance, if you only value those rooms being warm in the evenings for example, and they lose a lot of heat if they are hot during the day, then chasing COP for its own sake could get silly?
clockworks said:
System has 2 variable speed pumps and a low-loss header. I can see the flow rate through the heat pump, and the temperature difference on the flow and return, on the control panel and app.
I can also monitor each radiator for temp drop with a dual-probe meter.
Presumably I can adjust the first pump's speed to get the flow and delta on the heatpump, then use the secondary pump to get the right sort of delta on the rads?
Presumably the low loss header and additional pump have been put in by the installers - they are unnecessary for such a small capacity unit - but it does mean you can have thermostatic valves on a number of rads (a couple still need to be fully open all the time). I can also monitor each radiator for temp drop with a dual-probe meter.
Presumably I can adjust the first pump's speed to get the flow and delta on the heatpump, then use the secondary pump to get the right sort of delta on the rads?
Aim to keep the flow and return temps within five degrees of each other, and you won't go far wrong.
ETA. As gareth h points out, it is generally reckoned you lose 3% efficiency with every degree increase in temperature rise. Hence, if the temp rise is 13 degrees rather than 3, that is a compounded loss of 35% efficiency.
Setting a temperature output from a heat pump by modulating the circulating pump is wrong.
Edited by caziques on Sunday 22 December 01:09
caziques said:
Presumably the low loss header and additional pump have been put in by the installers - they are unnecessary for such a small capacity unit - but it does mean you can have thermostatic valves on a number of rads (a couple still need to be fully open all the time).
Aim to keep the flow and return temps within five degrees of each other, and you won't go far wrong.
ETA. As gareth h points out, it is generally reckoned you lose 3% efficiency with every degree increase in temperature rise. Hence, if the temp rise is 13 degrees rather than 3, that is a compounded loss of 35% efficiency.
Setting a temperature output from a heat pump by modulating the circulating pump is wrong.
Installer said they now fit the low loss header as standard, as they were getting issues where homeowners were closing all their rads with TRVs, despite being told to leave some "open".Aim to keep the flow and return temps within five degrees of each other, and you won't go far wrong.
ETA. As gareth h points out, it is generally reckoned you lose 3% efficiency with every degree increase in temperature rise. Hence, if the temp rise is 13 degrees rather than 3, that is a compounded loss of 35% efficiency.
Setting a temperature output from a heat pump by modulating the circulating pump is wrong.
Edited by caziques on Sunday 22 December 01:09
I've got 2 "open" rads.
I meant "use the pump speed on the primary to keep the delta between primary flow and return within spec", not the actual flow temperature.
The pumps are Evosta, 3 speeds and 3 response settings - open, TRV and UFH.
The primary pump is using the open setting, low speed.
The secondary pump is using the TRV setting, medium speed.
Looking at the ASHP app, the flow and return temp difference hour by hour is between 2 and 4 degrees.
I've been round all the rads rebalancing them, aiming for a 1 to 2 degree drop (meter with 2 clamp thermistors) while keeping the surface temp as even as possible (Topdon thermal imaging camera).
I've not checked the overall temp drop on the secondary circuit yet.
I've just watched the Heatgeek video on "micro zoning", and how it can save heat loss, but actually end up using more energy and costing more.
I fitted an Evohome setup quite a few years ago, non-condensing oil boiler. It did actually save a bit on oil usage, just heating the rooms while they were occupied or about to be occupied.
I left the Evohome gear in place, but having watched the video, I've just been round and modified all the schedules. Instead of dropping the temps of "unoccupied" rooms (zones) down to 15 degrees, I've increased that to 1 degree below the adjacent rooms.
One thing I'm unsure about is how it affects heatpumps using weather compensation curves rather than room compensation. With room compensation, the "open" rads would have to work harder (increased flow temps, lower efficiency) to make up for heat lost to unheated rooms.
With weather compensation, isn't the flow temp (and efficiency) fixed by the outside temperature? With weather comp, the running rads would be on for longer, but the flow temp would remain the same. Some savings from less cycling, but not from lower flow temps, without zoning.
I'd always assumed that an internal wall and closed door would be pretty good at isolating one room from another. Seems I was wrong about that.
Who knew that something as seemingly simple as keeping warm could be so complex!
I fitted an Evohome setup quite a few years ago, non-condensing oil boiler. It did actually save a bit on oil usage, just heating the rooms while they were occupied or about to be occupied.
I left the Evohome gear in place, but having watched the video, I've just been round and modified all the schedules. Instead of dropping the temps of "unoccupied" rooms (zones) down to 15 degrees, I've increased that to 1 degree below the adjacent rooms.
One thing I'm unsure about is how it affects heatpumps using weather compensation curves rather than room compensation. With room compensation, the "open" rads would have to work harder (increased flow temps, lower efficiency) to make up for heat lost to unheated rooms.
With weather compensation, isn't the flow temp (and efficiency) fixed by the outside temperature? With weather comp, the running rads would be on for longer, but the flow temp would remain the same. Some savings from less cycling, but not from lower flow temps, without zoning.
I'd always assumed that an internal wall and closed door would be pretty good at isolating one room from another. Seems I was wrong about that.
Who knew that something as seemingly simple as keeping warm could be so complex!
clockworks said:
I've just watched the Heatgeek video on "micro zoning", and how it can save heat loss, but actually end up using more energy and costing more.
<snip>
Heat Geek is a great resource - learnt a heck of a lot from them. Urban Plumbers channel on YT is also worth a visit<snip>
clockworks said:
<snip>
With weather compensation, isn't the flow temp (and efficiency) fixed by the outside temperature? With weather comp, the running rads would be on for longer, but the flow temp would remain the same. Some savings from less cycling, but not from lower flow temps, without zoning.
With WC the relationship between the outside temp and flow temp is what is set by the compensation curveWith weather compensation, isn't the flow temp (and efficiency) fixed by the outside temperature? With weather comp, the running rads would be on for longer, but the flow temp would remain the same. Some savings from less cycling, but not from lower flow temps, without zoning.
It isn't normally linear due to heat losses increasing as outside temperature drops
The whole point of WC is to replace the heat lost - The flow temp should rise as the outside temp falls and the heat pump will cycle less - it won't remain the same but be on for longer
clockworks said:
I'd always assumed that an internal wall and closed door would be pretty good at isolating one room from another. Seems I was wrong about that.
Heat always moves to cold - doesn't mater if it's doors or walls in the way it's gonna moveclockworks said:
Who knew that something as seemingly simple as keeping warm could be so complex!
I think it's as complex as you make it I know I'm running a gas boiler rather than heat pump but with a steady 6 deg outside today my flow temp has been pretty much a constant 31.5 deg C (WC curve 0.6) 4 Bed, 2 bath extended detached house with 13 rads (All sized to lower flow temps)
I have some rooms where the TRV's are intervening on a regular basis and others where the flow temp is not high enough to get the room to target temp (I have set an elevated target for the TRV and I have no expectation that it will be hit)
I'm trying to get to the stage where the majority of TRV's in the rooms we use a lot are never closing down the flows
Areas occasionally used are on scheduled heating slots and respond quickly temp wise when TRV's open
My aim is to get rid of the majority of TRV's and run it purely on WC (to go from 13 TRV's to 5)
I've posted some more stuff on the "ASHP - are they any good" thread.
Basically, I think I've got my head around Weather Compensation, and have been tweaking down the flow temps. Currently 36 degrees with an outside temp of 8 today.
I've also reduced the zoning deltas to 2 degrees for adjacent rooms, 4 degrees maximum across the house.
It looks like I might need to upgrade 3 more radiators, but I'll see how it goes if we have any days close to zero.
I've added a Shelly energy monitor to the heat pump supply, and a Shelly outdoor temperature sensor. Both of these store data on the Shelly app.
Interesting to see how it modulated, and I can get accurate running cost figures (split out from the "whole house" numbers on the Zappi and Octoaid apps). This should allow me to make changes and see what they save (by comparing to other days with the same outside temperatures).
Basically, I think I've got my head around Weather Compensation, and have been tweaking down the flow temps. Currently 36 degrees with an outside temp of 8 today.
I've also reduced the zoning deltas to 2 degrees for adjacent rooms, 4 degrees maximum across the house.
It looks like I might need to upgrade 3 more radiators, but I'll see how it goes if we have any days close to zero.
I've added a Shelly energy monitor to the heat pump supply, and a Shelly outdoor temperature sensor. Both of these store data on the Shelly app.
Interesting to see how it modulated, and I can get accurate running cost figures (split out from the "whole house" numbers on the Zappi and Octoaid apps). This should allow me to make changes and see what they save (by comparing to other days with the same outside temperatures).
clockworks said:
I've posted some more stuff on the "ASHP - are they any good" thread.
Basically, I think I've got my head around Weather Compensation, and have been tweaking down the flow temps. Currently 36 degrees with an outside temp of 8 today.
I've also reduced the zoning deltas to 2 degrees for adjacent rooms, 4 degrees maximum across the house.
It looks like I might need to upgrade 3 more radiators, but I'll see how it goes if we have any days close to zero.
I've added a Shelly energy monitor to the heat pump supply, and a Shelly outdoor temperature sensor. Both of these store data on the Shelly app.
Interesting to see how it modulated, and I can get accurate running cost figures (split out from the "whole house" numbers on the Zappi and Octoaid apps). This should allow me to make changes and see what they save (by comparing to other days with the same outside temperatures).
HDD is the key to understanding how your system performs v outside tempsBasically, I think I've got my head around Weather Compensation, and have been tweaking down the flow temps. Currently 36 degrees with an outside temp of 8 today.
I've also reduced the zoning deltas to 2 degrees for adjacent rooms, 4 degrees maximum across the house.
It looks like I might need to upgrade 3 more radiators, but I'll see how it goes if we have any days close to zero.
I've added a Shelly energy monitor to the heat pump supply, and a Shelly outdoor temperature sensor. Both of these store data on the Shelly app.
Interesting to see how it modulated, and I can get accurate running cost figures (split out from the "whole house" numbers on the Zappi and Octoaid apps). This should allow me to make changes and see what they save (by comparing to other days with the same outside temperatures).
https://www.degreedays.net/?gad_source=1&gclid...
Stick your postcode in - get the HDD data by day and then compare with energy used
B'stard Child said:
HDD is the key to understanding how your system performs v outside temps
https://www.degreedays.net/?gad_source=1&gclid...
Stick your postcode in - get the HDD data by day and then compare with energy used
I had a read of how it works, and it seems like a simple and useful concept.https://www.degreedays.net/?gad_source=1&gclid...
Stick your postcode in - get the HDD data by day and then compare with energy used
I set my local weather station (Culdrose), and base temp of 19.5, 12 months of daily data.
First issue was, the date in the table just shows as a series of hashes? If I click on a cell containing hashes, the date shows up at the top though. Might be because I'm using an Android tablet?
If I look at yesterday's number - 10.9 - that tallies with the fairly consistent outside temp of 8 and a bit degrees that my weather station showed. The average outside temperature was 10.9 degrees below my chosen 19.5 base.
However, looking through the whole table, the lowest number I could find was 0.9. Most days in the summer were between 1 and 4. Obviously, because the temperature at night is lower than the base temperature by a bigger margin than the day temp is above the base temp.
All perfectly logical.
So how come I can have the heating off from May to September and not feel cold?
There is obviously some "background heating" going on from 2 people, a cat, and the house base load of 360 watts.
The biggie though is solar gain, which HDD numbers don't reflect.
On a sunny day, even when it's 6 degrees outside, I can open the door into the conservatory and raise the temp in the kitchen/diner to 23 degrees. Only works until early afternoon, then the conservatory is in the shadow of the house, and temps drop again.
Similar effect in the afternoon, when the sun heats the flat roof of the dormer, and streams into the big windows of the lounge.
To be properly useful, I think the basic HDD number would need to be modified with "sunlight hours", and the solar gain characteristics of my house.
Probably need wind, rain and humidity data too, as I think damp/wet exterior walls would draw more heat from the house on a windy day?
clockworks said:
B'stard Child said:
HDD is the key to understanding how your system performs v outside temps
https://www.degreedays.net/?gad_source=1&gclid...
Stick your postcode in - get the HDD data by day and then compare with energy used
I had a read of how it works, and it seems like a simple and useful concept.https://www.degreedays.net/?gad_source=1&gclid...
Stick your postcode in - get the HDD data by day and then compare with energy used
I set my local weather station (Culdrose), and base temp of 19.5, 12 months of daily data.
First issue was, the date in the table just shows as a series of hashes? If I click on a cell containing hashes, the date shows up at the top though. Might be because I'm using an Android tablet?
If I look at yesterday's number - 10.9 - that tallies with the fairly consistent outside temp of 8 and a bit degrees that my weather station showed. The average outside temperature was 10.9 degrees below my chosen 19.5 base.
However, looking through the whole table, the lowest number I could find was 0.9. Most days in the summer were between 1 and 4. Obviously, because the temperature at night is lower than the base temperature by a bigger margin than the day temp is above the base temp.
All perfectly logical.
So how come I can have the heating off from May to September and not feel cold?
There is obviously some "background heating" going on from 2 people, a cat, and the house base load of 360 watts.
The biggie though is solar gain, which HDD numbers don't reflect.
On a sunny day, even when it's 6 degrees outside, I can open the door into the conservatory and raise the temp in the kitchen/diner to 23 degrees. Only works until early afternoon, then the conservatory is in the shadow of the house, and temps drop again.
Similar effect in the afternoon, when the sun heats the flat roof of the dormer, and streams into the big windows of the lounge.
To be properly useful, I think the basic HDD number would need to be modified with "sunlight hours", and the solar gain characteristics of my house.
Probably need wind, rain and humidity data too, as I think damp/wet exterior walls would draw more heat from the house on a windy day?
My target is less than 4.0 kWh per HDD (but that was worked out with scheduled heating - running currently at 4.0 to 5.0 kWh per HDD and I’m OK with that.
Download it on a PC with excel it’s easier to manage the data
Yes it’s not going to account for wind, rain or solar gain on south facing glazing but it’s been invaluable for me to compare improvements to the house I have
Data from 2020 & 2021 showed I used to be using 8.0 kWh per HDD
OK, so basically use it as a long term comparison tool to check improvements, rather than just for day to day number-crunching?
That makes sense, as solar gain/wind effects would likely average out if looked at annually or season by season.
I guess the way to arrive at a realistic base temp would be to tweak the number until the zero HDD period matched up with the "turn off the heating" period?
That makes sense, as solar gain/wind effects would likely average out if looked at annually or season by season.
I guess the way to arrive at a realistic base temp would be to tweak the number until the zero HDD period matched up with the "turn off the heating" period?
clockworks said:
OK, so basically use it as a long term comparison tool to check improvements, rather than just for day to day number-crunching?
That makes sense, as solar gain/wind effects would likely average out if looked at annually or season by season.
I guess the way to arrive at a realistic base temp would be to tweak the number until the zero HDD period matched up with the "turn off the heating" period?
Or use their regression tool and stick in your annual kWh equivilent of oil maybe?That makes sense, as solar gain/wind effects would likely average out if looked at annually or season by season.
I guess the way to arrive at a realistic base temp would be to tweak the number until the zero HDD period matched up with the "turn off the heating" period?
B'stard Child said:
Or use their regression tool and stick in your annual kWh equivilent of oil maybe?
I'll have a look at that.Our oil consumption has been pretty consistent - one delivery a year, between 800 and 900 litres - so around 8000kWH of heat after efficiency losses.
We did use much more aggressive zoning (Evohome smart TRV in each room) to get that low though.
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