Am I right in thinking the second set point is configured using the zone 2 settings?
Yes, but if you don't have zone valves etc, heat pump just ramps up and down temp as required to the single zone. I use the same input on mine to ramp up during excess PV.
So once again, internal temp comes up as the deciding factor. How you get to that temp and maintain it will always be debated, but all heating / cooling is done by deciding that internal temp. So why not start and work with that, rather than trying to match the external temp to what it might be/not be to achieve it
Because of the lag in response. Simple as that. Look to control theory to explain why this is a problem. If your house has the thermal characteristics of a tent then basing control on IAT works perfectly, most houses have significant heat capacity and thus lag which messes with the control.
If you have a heat pump or a boiler with WC I suggest you try it. You may be surprised by how well it works particularly given your location (When I got my heat pump I tried WC with and without a mild iat influence, pure WC was unquestionably better). Obviously I know nothing about your house so there may be a reason why it won't work well for you.
It does require a leap of faith and does take a bit of time to get right but the science and engineering is sound and the improvements in comfort (and cost) very real so it's a leap well worth trying.
It's unfortunate that, because it takes a bit of time to get right and can only really be done in the heating season, installers can't really be expected to adjust WC parameters optimally. This is where some heat pumps, particularly but not exclusively those of european origin, arguably have a bit of an advantage because they have been forced to develop a UI to WC for boilers that can perhaps be more easily explained to the non techy person (basically if you are too cold turn the digital knob up, if you are too warm do the opposite, don't adjust more than once per day and once it's generally right, leave it). That said adjusting one with the more common 4point system is hardly challenging.
WC is of course inextricably linked to low temperature heating. This also improves comfort and reduces cost. For example I have gone progressively from a gas boiler at FT 75 (IE where the maintainer left it) to the same gas boiler at FT 50 (the lowest it will go) to a heat pump at FT 42-27. Each step reduced cost by roughly 10 percent (so 20pc total) and increased comfort. Furthermore my whole house is now heated to a comfortable temperature 24*7 rather than fiddling with TRVs and timers (and even at one point smart trvs) to try to save money and control things over which, in reality, I have little or no control because of the house thermal capacity.
The manufacturers of 'smart' controls have led us on a journey over the past 40 years to a place which benefits them, but frequently disadvantages us. The UK heating industry shunned WC for boilers and set up our condensing boilers so that they don't condense, reducing our comfort and increasing our bills by 10% approximately. The discontinuity of the transition to heat pumps is an opportunity to do a reset and KISS.
Seriously, if you have a heating system capable of WC, give it a try. You may well be pleasantly surprised.
This post was modified 3 hours ago 4 times by JamesPa
This post was modified 2 hours ago 2 times by JamesPa
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.
Several of those are irrelevant. For the ones that are relevant, if you work out the energy difference due to these, it's mostly negligible compared to the heat capacity (stored energy) in the house, so these generally result mostly in minor temperature deviations which are mostly much less than the error caused by the delay in a indoor sensor based control loop
Hi James, I would slightly disagree with this and maybe we are outliers due to our location but wind is a huge factor for us, which means I also agree with you very much that a control based system is the way to go (again for us!).
That's fair enough, I did say that there are exceptions (I think the only significant ones may be wind and solar gain) and there is no perfect solution that fits every house. My only contention is that WC is the best starting point in the vast majority of (possibly even all) cases but some tweaks as an overlay may be necessary depending on individual sotuations.
My own house likewise benefits from significant solar gain. In March/April (having run for the rest of the season on pure WC), I switched on a limiting function on my hp (as an overlay to the WC) which switches the heat pump off when the room temperature goes more than about half a degree above the set value. I will revert to pure WC once the heating season starts up again. I think @johnmo has suggested above a way you might deal with wind as an overlay to WC.
Am I right in thinking the second set point is configured using the zone 2 settings?
Yes, but if you don't have zone valves etc, heat pump just ramps up and down temp as required to the single zone. I use the same input on mine to ramp up during excess PV.
Got you I will look at implementing this cheers!
Kind Regards
Si
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Grant Aerona3 13kW
13 x 435w Solar Panels
Solax 3.5kW Hybrid Inverter
Several of those are irrelevant. For the ones that are relevant, if you work out the energy difference due to these, it's mostly negligible compared to the heat capacity (stored energy) in the house, so these generally result mostly in minor temperature deviations which are mostly much less than the error caused by the delay in a indoor sensor based control loop
Hi James, I would slightly disagree with this and maybe we are outliers due to our location but wind is a huge factor for us, which means I also agree with you very much that a control based system is the way to go (again for us!).
This is why I am trying to factor in IAT, OAT, weather forecast, weather actual, solar days, etc whilst giving Commander in Chief Domestic granular control if she is too hot or too cold! And as my tiny mind can only cope with so much, I am using AI to try and help me solve this problem.
This is how I would set it up
Firstly a WC curve tuned to house. Start at 20 Deg outside and min flow temp of heat pump 20 or 25. End point at your design outside temp say -3 or -5, for radiators set to 45 and UFH at 35. For the windy days where the house temperature drops more than expected, the Grant/Chofu heat pump has a set of terminals for a second set point, connect a wireless thermostat that. Set the set point 1 or 2 deg above the normal WC base temp. Computherm do a nice variable hysterisis thermostat Q20RF can get from Amazon.
So your general heating is all done via WC, if the house drops in temperature your second set point comes into play and adds heat for you automatically.
Tuning
In heating season, set second point thermostat out of the way set to max, tune only once every 24 hrs, if to warm tune only the high flow temp setting down 1 Deg, repeat every 24 hrs. Until comfortable, then bring in thermostat , you will need to run hysterisis to suit your comfort, under and overshoot.
No weather forecast which are usually crap, sensors that decides to go off line, and a system no-one can fix except you. Smart stuff has a place, but it isn't for control of heating systems. We were supposed to 30kWh of yesterday, but it was foggy all day, got nearer 3kWh. Shelly H&T also went offline for no reason for a couple of hours then came back on, but only use to to log data, that will be going as well pretty soon.
Sorry what you are doing is fine for monitoring only, but utter rubbish for heating control, it just isn't robust enough. Been there, done it, got the bloody tee shirt, wife utterly pissed off. KISS wins every time, heating has never run better, getting rid of the useless tatt, additional pumps, no buffers, no mixers, no internet anything, you don't even need a thermostat really.
Make sure your outdoor sensor on the ASHP doesn't get affected by the sun would be my input.
I really couldn't agree more with this. Heating control is mission critical and needs to survive internet outage and death of the 'clever' owner. HA and the like are fine for monitoring and experimenting with control changes prior to implementing them, but not for long term mission critical control
The only suggestion I can think of that might be worth considering in addition to the above is using a wind sensor to trigger the uplift in ft. That might avoid a lag in response (much like WC itself does) and consequent risk of oscillation. I don't know if a suitable sensor is readily available however nor do I know if the result would be better than the simple suggestion above.
This post was modified 2 hours ago 3 times by JamesPa
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.
@jamespa I have an Ecowitt weather station so this is in my plan. I am also building the system locally so no internet required and so that it fails safe so it can easily be controlled by the EPH dumb controls if anything goes wrong.
Kind Regards
Si
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Grant Aerona3 13kW
13 x 435w Solar Panels
Solax 3.5kW Hybrid Inverter
There is a lag in response no matter which you chose, depending on the mass of the heat sink and ours is large. There would also be a build up of heat, as nothing can know exactly how much heat a house will lose at anyone time due to various factors involved.
I have and still sometimes use WC, but my curve is 28/25 to 30/-5, so a very shallow curve and it works just fine at one flow temp.
Our whole system was set up to run at 35°c, but have since found we can run it as low as 25°, but then it start to cycle after about 12hrs. So taking results from all the various experiments I've done, the best solution was to set a decent flow temp and let the HP turn on / off as the internal temp went down. Ensuring we had 21° at 16.00hrs, so it could be off all evening and still stay warm. Our internal temp does not differ by more than 1° across the whole of the house.
Also, as we run the HP, mainly during the day and so low, we don't suffer from defrost cycling and the HP itself is normally off before flow cycling takes place. It means our compressor is on, most of that time and uses less that 1kw per hour, while running.
As for costings, 1300kwh cost less than £200 per year to heat our house. Which with some further adjustments we can get down to £100
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