Smart TRV's

[Tilerdon]

A bathroom 4°C below setpoint not calling for heat sounds frankly crazy.

I'm sorry Ric I think you may have misread that - The Actual Temperature in the Bathroom was 19 with the Set Temperature at 15 not the reverse. I just wanted it a little warmer.

There are a number of factors that have made me follow this route. I'm 73 years old and will probably only be in this house for another few years, certainly not long enough for there to be any payback on a boiler replacement and probably not even by installing new and better sized and distributed radiators. The rooms in this bungalow are very large as are the windows. The Lounge , main bedroom and hallway all have SSW facing windows. The Lounge is about 25 sq metres with a single radiator and even the hallway where the wall thermostat is located is close on 14 sq metres with a half glazed door with side panels about 2.5 metres wide, so quite susceptible to temperature change from the late afternoon/early evening sun or from opening the external doors at either end. It certainly isn't the best place to have a thermostat to control the overall house temperature but that is where it is. I have tried a Honeywell Sundial thermostat but it wasn't hugely successful.

With weather as it is at the moment, dull one moment and blazing sunshine the next I'm already seeing the benefits in terms of comfort. To be able to tweak the set temperature on the radiator whilst sitting in my chair is already worth the relatively small amount I have spent. Also when I come to leave the property, an hours work in fitting the old valveheads back and 5 minutes disconnecting and reconfiguring the remote boiler switch and, the system will be back to a operable "standard" dumb state.

If I find that what I have done does not work effectively I merely have to re-program the hall thermostat, turn the boiler programmer back to Auto and disable the piece of software that switches the boiler on or off right now but at the same time I can still keep the individual room programmes in the valves but know that the hall thermostat will control the maximum temperature at any moment in time.

I did find this website when I was researching Short Cycling - Boiler Short Cycling - http://www.home-heating-systems-and-solutions.com/boiler-short-cycling.html and was interested to read this

solution. Which is effectively what I'm doing except I have 10 Thermostats

 

[Tilerdon]

As Chuck mentioned before, the simplest way to control individual rooms via TRVs is by using a buffer tank and a smart pump. Then you don't need any room thermostats or zone valves, and you can get rid of the bypass (maybe the tank would fit there?), and program each TRV for whatever temperature schedule you want in each room.

Firstly I only have 2 zone valves which isolate the central heating and hot water circuits from one another. The only room Thermostat that I have is now set to 35°c 24 hours a day so it is constantly on and the WiFi TRV's control the temperatures in each of the rooms . I don't want to get rid of the radiator which serves as a by-pass (which I probably don't need) because it warms the airing cupboard . I still need to research Smart pumps but there don't seem to be many available at present and I suspect that the big cast iron heat exchanger in my 20 year old very dumb boiler acts as its own buffer. After having the heating switched off for 30 minutes, the radiator in my kitchen became too hot to hold your hand against for any period of time in less than a minute after switching the heating on again.

Thanks for your input.

 

[siricosm]

Firstly I only have 2 zone valves which isolate the central heating and hot water circuits from one another. The only room Thermostat that I have is now set to 35°c 24 hours a day so it is constantly on and the WiFi TRV's control the temperatures in each of the rooms . I don't want to get rid of the radiator which serves as a by-pass (which I probably don't need) because it warms the airing cupboard . I still need to research Smart pumps but there don't seem to be many available at present and I suspect that the big cast iron heat exchanger in my 20 year old very dumb boiler acts as its own buffer. After having the heating switched off for 30 minutes, the radiator in my kitchen became too hot to hold your hand against for any period of time in less than a minute after switching the heating on again.

Thanks for your input.

Sorry, I should clarify. By "smart" pump, I didn't mean something fancy with Wifi or remote control features or anything like that, I meant a pump that modulates, so that when the TRVs open, they pump more. They are very common now. You leave the pump on all the time you want heating available, and when the TRVs are all closed, it will throttle down to a few watts. When one or more TRVs open, it will pump faster. You hook that to a buffer tank which provides the supply of hot water, which is always there whether the boiler is on or not. The boiler then heats the tank to a fixed temperature with a simple cylinder stat, so there is no cycling and no bypass required. Ideally, the tank should be large enough that the boiler can run at least 5-10 minutes to satisfy the thermostat differential.

A buffered heating system is the only way I can think of to truly have one zone per TRV, and it avoids the boiler firing all the time when you only need a few kW of heat.

Reading the thread I understand that you are not interested in making substantial changes like that, as it would cost a few hundred pounds. It was more of a comment really.

 

[Radian]

I do hope this two month old thread isn't too stale for me to contribute to, as I sympathise with Tilerdon's approach to his problem. I too have a home-brewed software control system and have found the extra few degrees of control that this gives me often makes it possible to work around issues using just the basic components already present.

I was wondering if Tilerdon might be able to monitor the temperature of the flow leaving the circulating pump and 'gate' the demand on the boiler firing according to the current amount of heat already flowing through the heat exchanger (which evidently has a significant time-constant) and the differences in setpoint and actual room temperatures. This all depends on the level of access the software has to these parameters. It also means controlling the circulating pump independently of the boiler electrical input as it would need to be operational all the while there was any demand (unlike the boiler).

 

[John.g]

The above is very interesting re buffering etc, yet you have systems like evohome that give very tight control of room temperatures and will fire the boiler continuously if any room is > than something like 1/1.5C below its setpoint and when less than this will cycle the boiler with on times as low as 1 min on and 9 min off, 6 cycles/hour, these settings are settable. Still, cycling the boiler very frequently is the main modus operandi.
I also think that even if the total energy demand is > than the boiler min output that it continues in this fashion, surely the system can summate the individual room HR92 controllers and when > the calculated boiler min output would fire it continuously as a large proportion of heating demand is within the (gas) boiler(s) modulation.

I have a 20kw oil fired boiler with 10 rads, 8 with TRVs and a room stat with another TRVd rad in the same (big) room with a non TRVd rad, the roonstat is set to 22C and all the other TRVs set to maintain 20C downstairs and 16/18C upstairs, this results in the boiler running (cycling as a OF boiler must) ) continuously for the 17 hour heating day and gives excellent control, the only very large room facing south can deviate by ~ 1.5/2 C before correction due to the solar effect as the room has a very large window area, because even though a TRV has a very small hysteresis it is relatively slow in response due to lag time in heating/cooling the liquid/wax filled actuator.