No luck…
I try ti use PID control, i set 19celsius indoor. Isteresis 0.4
The heating start and temperature reach 19.4 then heating stop and temperature drop to 18.6 now heating restart. This Is not modulation.
Another questione in home assistant Is not possibile to set PID parameter.
You can use the ds18b20 sensor on the “heater B” return pipe 
Modulation is controlled by the boiler. Adjust the PID coefficients and everything will be fine.
But I try to change it, but I don’t see variation in the curve. Where I see the formula for calculate the target heating temperature. Thanks
I know is not use curve, but is impossible to set the parameter is I don’t know the formula or the means of all parameter.
The major “problem” - difficult with this system is that with isteresis if the target temperature reach the max it don’t restart before it reach the min value.
I don’t know how to answer your question. Using PID implies that you understand how it works or are willing to learn how it works. There are a lot of abstruse articles on Google, but I think you can find a simpler explanation on YouTube.
I would not like to repeat what has already been explained dozens of times before me (and perhaps better than I could explain). The only thing I can say is that it is impossible to choose universal coefficients, they will differ for different heating systems and different houses. And they are configured only experimentally by testing.
But I can give you a piece of advice: it would be better to start with setting dt - this is the system’s reaction time in seconds to a change in temperature in the house. I usually find this value in the statistical graphs in home assistant.
Hi all. Looking for a bit of advice with the OT gateway - can it take a feed from 2 thermostats, aggregate values and then go into a single OT port on an OT capable boiler? Or so I need 2 gateways (one thermostat into each gateway) and then somehow joining the 2 gateways to go to one OT boiler port?
So my setup is a Potterton Promax Ultra 40 combi boiler. We also have 2 x Nest 3rd gen thermostats. The central heating is zoned (upstairs and downstairs) - one central heating pipe comes out of the boiler. The boiler CH pipe then goes to 2 motorised valves that are Myson Power Extra (I’m guessing the thermostats have been wired direct to the valves to send open/close signal to the appropriate value and maybe a wire from the valves go to the boiler to call for heat? I have pics of the wiring but am not sure as can’t trace everything).
The boiler is OpenTherm capable (1 port). The Thermostats are also OpenTherm capable.
The thermostats are currently set up with traditional On/Off. we would like to change this to use the OpenTherm capabilities
OpenTherm does not allow multiple devices to be connected to a bus. You can connect the nest heat link to the esp via the cascade control input, see this and this.
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Thank you @LazyDev. Sadly I’m not knowledgeable enough to understand this fully (I joined the Telegram group and am looking at the English thread). For example, I don’t think I need the hot water connected part? - my heatlinks have wires coming out of N, L, 2(which is jumpered to L), 3, T1 and T2
I believe the heatlink cables go into this box and then go on to boiler/valves
The single pipe out of the valves goes on to the boiler (the white box on the left is the pic above).
The reason I thought the aggregate option might have worked was due to OpenTherm 2+ zones | DIYnot Forums. I wonder how this system would allow up to 6 zones on OT? https://www.youtube.com/watch?v=sfHXnC67kwc
Would this setup require 1 ESP board and have both heatlinks plugged into the 1 board? Or is it a board for each heatlink? Do the boards then get connected to the 2 OpenTherm points in the boiler? Or do they go into an OT gateway and then on to the OT points in the boiler?
Why PID and Equiterm factor is not enable in home assistant?
Your nest is not connected to the boiler via opentherm. OT does not support multi-zone. Very few boilers allow you to control the “second zone” - the second pump/tap, but this is not implemented in the firmware. To control zone taps/pumps you need to use another solution. For example Kincony KC868-A8 with esphome.
Thank you @LazyDev. I guess an alternative solution as well would be to set both the zone valves to open (effectively turning the system back to a 1 zone central heating system and all radiators will heat up), and then use the downstairs Nest thermostat (primary living area) with its HeatLink directly wired to the boiler OT inputs. That way, I would have OT capabilities, I’m just not sure if that option would ultimately be more energy efficient and use more gas or less in the long run for heating the property (3 bed, average UK size, built 2018 so relatively well insulated). My current Nest heating schedules are:
Downstairs zone
Upstairs zone
I have a script and automations in HA setup so that if its a bit chilli, I can boost heating by zone for a period that I can define, up to an hour (something that I feel native Nest app is missing).
Any thoughts on that? Is OT going to make a difference to gas usage?
If you run with reduced flow temperatures (to be more precise, a low return temp), then efficiency will increase as the boiler is pushed further in to condensing mode.
I let my thermostat set the boiler to between 40°C and 60°C for a return temperature of 35-40°C. Efficiency is between 92% and 96% - Not much of a spread, but much better than the 86% I’d get with the boiler running at 70°C all the time.
But (there is always a but), if your radiators can not dissipate the heat that the boiler is producing it will start to short cycle (bad for efficiency). My boiler will modulate down to ~3.2kW, and at 40°C, the radiators will use that heat. If/when a TRV or two kick in, I loose capacity and the boiler starts short cycling.
@paul_c5x4 thank you. I currently run the boiler temp at 59°. I have a button on the boiler that can show me return flow temp which is generally around 55° but obviously it’s a full pelt for burning gas (which I believe the 55° is in the condensing return flow range?)
According to the manual, my boiler is a 5:1 ratio which I recall being able to modulate down to around 6kW. I wonder if there is a way I can test out if the rads can dissipate the heat? Would that work if I set return flow temp to 40°?
By TRV kicking in, do you have old school TRVs with 5 settings (plus an off)? I don’t understand what you mean about loosing capacity from the TRV
If your boiler is running at 60°C, ideally, the return wants to be 60*0.7=42°C - If the return temperature is higher, then I’d suggest looking at the balance of all radiators and possibly reducing the pump speed if you can (I have my pump on the lowest setting).
Condensing only really kicks in at 54°C, so the lower the return temperature, the better. At 55°C, you’re probably only getting 86%, so plenty of scope to improve on that.
I have a heat meter (an L&G T230) plumbed in to the heating system. This gives a pretty good idea of how much heat is being put out by the radiators. If you know the flow & return temperatures along with the flow rate, it is a trivial calculation to work out how much energy has been consumed. From my notes:
The specific heat of water is 4190 J/(kg⋅°C). It means that it takes 4190 Joules to heat 1kg of water by 1°C. Heat required to raise the temperature, Qt: Qt = cm*ΔT where: Qt is the specific heat capacity; cm is the mass; ΔT is the temperature differential Or: kWh = cm*ΔT*c c is specific heat of water divided by time: 4190/3600 = 1.163889
Looking at tables for my radiators, I know what each one is rated at based on a flow temperature of 70°C (often quoted as ΔT50). Using correction tables (e.g. https://www.clyderadiators.co.uk/delta-t-conversion ), one can work out how much heat will be radiated at a particular flow temperature. I have a total of 12.5kW of radiators, so at 40°C (ΔT20), my limit is 3.75kW - These figures are based on a room temperature of 20°C.
When a TRV (old skool 0-5 numbers) kicks in, it stops water flowing through the radiator. Effectively, taking that radiator out of the equation. As a result, the system is not able to dissipate as much heat.
Below, a plot showing flow/return temperatures and power dissipated by the radiators.
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@paul_c5x4 wow, thanks for the info. I have more research to do!
lol all my rads TRVs are set to the highest number to get as much heat out in to the rooms as quick as possible and room target temp is 23° for WAF, but see I should do some calcs
TRVs do not regulate the amount of heat being put out by a radiator. All it can do is turn the radiator off as the room gets up to temperature.
Same for the thermostat - Turning that up does not make the house heat up any quicker.
To heat a house up faster, you either need to fit larger radiators (impractical if you just need the occasional boost), or crank up the boiler temperature. However, that reduces efficiency and also increases the rate of corrosion inside your radiators. Go too high, and there is also the risk of burns if you touch the radiators - A very real danger for the elderly and small children.
Heat Geek is a good place to start if you want to know more about heating. Although primarily pushing heat pumps, much of what they have to say can be applied to gas boilers - I took on board quite a bit of their advice when replumbing my heating system with an eye on fitting a heat pump in the future. Bigger radiators, 22mm pipes for the bulk of the plumbing, and so on. Running the boiler at 40°C, I can heat the place reasonably well. Heat pumps will run at a similar temperature, so I’m set should the boiler pack up.
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