TRVs vs. zoned heating?

ZV Yoda

We need to have some work done to our boiler this week & have a plumber organised. Got me thinking about heating controls. We have 17 rads in the house - all with TRVs. While the TRVs do the job, I'm wondering if we'd benefit from getting the system zoned. Would it be a more cost effective way to regulate the heating over the long term?

It's not zoned at present - although we do have a "summertime cutoff valve" in the hotpress that allows us to switch off all rads. This means the boiler just heats the tap water.

If it makes any difference, the house has three floors inc attic conversion. The boiler is a Potterton Promax HE 32. We also have an electric immersion heater which rarely (if ever) gets used.

shane 007

TRV'S provide no boiler interlock & will be a large factor leading to boiler short cycling. This puts unnecessary wear & tear on boiler components, decrease boiler life span & uses considerably more fuel. Also during ignition & shut down process there is unburnt gas during this process.
A large degree of assistance to eliminate a large proportion of this is boiler interlock with decent controls, such as time & temperature control of each zone. So instead of having the heating on in a particular zone for 3 hours, the thermostat for that zone is possibly satisfied after 30 minutes & shuts down the boiler until the temperature falls below the desired level. Ultimately, you are heating where you want when you want, instead of heating all of the home when you are only using part of it.

Manufacturer's are striving to increase their modulation rates to suit much lower satisfied demands when decent insulation levels are beginning to surface in Ireland.
Outdoor weather compensation is the future IMHO.

ZV Yoda

shane 007 wrote: »

TRV'S provide no boiler interlock & will be a large factor leading to boiler short cycling. This puts unnecessary wear & tear on boiler components, decrease boiler life span & uses considerably more fuel. Also during ignition & shut down process there is unburnt gas during this process.
A large degree of assistance to eliminate a large proportion of this is boiler interlock with decent controls, such as time & temperature control of each zone. So instead of having the heating on in a particular zone for 3 hours, the thermostat for that zone is possibly satisfied after 30 minutes & shuts down the boiler until the temperature falls below the desired level. Ultimately, you are heating where you want when you want, instead of heating all of the home when you are only using part of it.

Manufacturer's are striving to increase their modulation rates to suit much lower satisfied demands when decent insulation levels are beginning to surface in Ireland.
Outdoor weather compensation is the future IMHO.

A few years back, we were advised (by a plumber) to install TRVs on all rads - so we did. They have a scale of 0 (off) to 5 (hottest). He said TRVs enabled us to control each room individually. Logically, this seemed to make sense to us - we typically have the 3rd floor TRVs at 1, 2nd floor at 2 & the ground floor at 3. I understood that this was the most efficient way to set them (since the top floor needs less heat than the ground floor).

Are you suggesting we should eliminate the TRVs & convert to a zoned system instead? I'm looking for the best long-term solution, but there seems to be a lot of conflicting info out there, so it's tough to know which option would work best for us.

antoinolachtnai

If you had a boiler controller that turned the boiler off and on depending on the outside temperature, that would largely eliminate the boiler short cycling. I have this, but it is something custom that I built. The newer boiler (my mum got the new viessmann this year) seem to be engineered so they would deal well with this sort of situation.

Weather compensation (where the 'set point' of the boiler reduces as the outdoor temperature increases) would eliminate this to a degree too but it might be tricky to get it to play well with your water heating needs. (40 degree water might be fine for heating your radiators, but it's damn-all use for heating your hot water.)

I can see shane's point, and if you were doing stuff from scratch, it is certainly the way to go. But I think the benefit would be marginal enough to go to a lot of trouble to refit. The reason is that if your house is not that big, it is really one heating area. There isn't that big a differential in temperature between one room and another and whenever you are home, you probably occupy the whole space, not just part of it. Of course it depends on how you actually live your life.

shane 007

ZV Yoda wrote: »

Are you suggesting we should eliminate the TRVs & convert to a zoned system instead? I'm looking for the best long-term solution, but there seems to be a lot of conflicting info out there, so it's tough to know which option would work best for us.

No, not at all. Keep the TRV's along with good controls. Just remember to remove the TRV heads where there is a room thermostat in the same room/area as they will conflict.

shane 007

antoinolachtnai wrote: »

If you had a boiler controller that turned the boiler off and on depending on the outside temperature, that would largely eliminate the boiler short cycling. I have this, but it is something custom that I built. The newer boiler (my mum got the new viessmann this year) seem to be engineered so they would deal well with this sort of situation.

Weather compensation (where the 'set point' of the boiler reduces as the outdoor temperature increases) would eliminate this to a degree too but it might be tricky to get it to play well with your water heating needs. (40 degree water might be fine for heating your radiators, but it's damn-all use for heating your hot water.)

I can see shane's point, and if you were doing stuff from scratch, it is certainly the way to go. But I think the benefit would be marginal enough to go to a lot of trouble to refit. The reason is that if your house is not that big, it is really one heating area. There isn't that big a differential in temperature between one room and another and whenever you are home, you probably occupy the whole space, not just part of it. Of course it depends on how you actually live your life.

Design temperatures would vary from room to room depending upon use, such as bathrooms would have a design temp of 22C due to the fact that you normally have no clothes on. Bedrooms would be 18C due to being covered with duvets, etc.
Living areas would be 20C.
Add 2C for young & elderly.

Weather compensation can generally be easily retrofitted.

ZV Yoda

Thanks for the responses. If we did zone the system, would keeping a TRV fully open work the same as removing it altogether?

I think the guy who installed our boiler (4 years ago) said that the boiler is smart enough to know the temp of incoming water and as a result, it self-regulates based on the temp differential. Is this the same as "weather compensation".. or is that something else altogether?

shane 007

ZV Yoda wrote: »

Thanks for the responses. If we did zone the system, would keeping a TRV fully open work the same as removing it altogether?

I think the guy who installed our boiler (4 years ago) said that the boiler is smart enough to know the temp of incoming water and as a result, it self-regulates based on the temp differential. Is this the same as "weather compensation".. or is that something else altogether?

You will need to remove the TRV head by just unscrewing it & keep it as a spare if any others become faulty.

Your boiler is a modulating boiler. That is different to weather compensation & open therm but it may accept it. It will depend on the PCB of the boiler. I would have to look it up or you could contact Potterton.

antoinolachtnai

shane 007 wrote: »

Design temperatures would vary from room to room depending upon use, such as bathrooms would have a design temp of 22C due to the fact that you normally have no clothes on. Bedrooms would be 18C due to being covered with duvets, etc.
Living areas would be 20C.
Add 2C for young & elderly.

Absolutely. A good way to provide for this would be TRVs. Zoning won't help much because bedrooms are generally next to bathrooms. My thought would be that zoning is good because you generally use the bedrooms at specific times of the day and TRVs are no use for scheduling.

Weather compensation can generally be easily retrofitted.

How can weather compensation be easily retrofitted where the same circuit serves both hot water and central heating at the same time?

shane 007

antoinolachtnai wrote: »

Absolutely. A good way to provide for this would be TRVs. Zoning won't help much because bedrooms are generally next to bathrooms. My thought would be that zoning is good because you generally use the bedrooms at specific times of the day and TRVs are no use for scheduling.

Radiator size will determine room temperature for a particular build dynamic. So, in order to achieve a higher room temperature beside a room that may have a 4C lower demand, the bathroom radiator will be sized to achieve a delta T of 25C. This is based on an average Irish temp of -3C outside. Bedroom would be 21C.

antoinolachtnai wrote: »

How can weather compensation be easily retrofitted where the same circuit serves both hot water and central heating at the same time?

By using the unused connection of the 3 connections (common, NO & NC) of the cylinder stat, wired back to the boiler PCB, the PCB will know the circuit has gone to HW demand so will raise the output temperature to 75C. Once satisfied or when there is space heating demand only, it will operate under compensated mode. No 4 pipe system required. The only difference will be when there is both HW & space heating demand, compensation will be switched off, but this should not be for long.

antoinolachtnai

shane 007 wrote: »

Radiator size will determine room temperature for a particular build dynamic. So, in order to achieve a higher room temperature beside a room that may have a 4C lower demand, the bathroom radiator will be sized to achieve a delta T of 25C. This is based on an average Irish temp of -3C outside. Bedroom would be 21C.

For sure, the radiator will determine the maximum temperature achievable. For the 360 days when it isn't -3, a TRV seems like a good way to get the right temperature.

By using the unused connection of the 3 connections (common, NO & NC) of the cylinder stat, wired back to the boiler PCB, the PCB will know the circuit has gone to HW demand so will raise the output temperature to 75C. Once satisfied or when there is space heating demand only, it will operate under compensated mode. No 4 pipe system required. The only difference will be when there is both HW & space heating demand, compensation will be switched off, but this should not be for long.

I agree, that is a very good solution, where there is an actuator valve on the central heating, and the boiler provides the facility.

shane 007

There a few issues with TRV's, namely they are fairly inaccurate with room temperature. Being so low to the ground & the radiator connecting heat to the upper part of the room, they rarely give an accurate enough comfort zone, without a lot of fiddling with them. I also find they rarely switch off unless they are set to a very low setting. The same seasonal adjustment would also apply with TEV's, hence best option is compensation. As long as the minimum outdoor temperature is not below this point too much, it does what it says on the tin.

Many gas boilers have already this function, it's just the manufacturers do not really broadcast it as it leads to some technical difficulties & the general public find it hard to comprehend a low temperature feel to the radiator when it is on. Most call backs on compensated systems are due to customers complaining of rads not hot enough. They think if the heating is on, the rads should be hot! It's a physchological thing!
Ariston & Vokera have it across their full range of boilers & are pretty much plug & play in their PCB's. Tomorrow's boiler will have standard compensation but the public & installers need to be dragged into at the moment. Enormous savings to be made.

shane 007

All Vokera's weather compensation run at the lowered output for 20 minute intervals. If the desired delta T between outdoor & indoor has not been achieved, it ramps up the flow temperature by 5C and so on every 20 minutes until this achieved.
The boiler temperature setting is read as the desired room temperature, i.e. 20C, etc. & can be adjusted +/- 5C.

JohnnieK

I've been fitting weather compensation for the last 4.5 year's and all bar one of them found it hard to understand.

The older generation find it hard to hard because the rads are not hopping off the wall.

The viessmann has a great system providing the 4 pipes can be used. And with the Ariston i like the way you can lock the out put temp for ta2 when hot water is called for and there modulating room stat is very good with weather comp and auto enabled.

Dtp1979

JohnnieK wrote: »

I've been fitting weather compensation for the last 4.5 year's and all bar one of them found it hard to understand.

The older generation find it hard to hard because the rads are not hopping off the wall.

The viessmann has a great system providing the 4 pipes can be used. And with the Ariston i like the way you can lock the out put temp for ta2 when hot water is called for and there modulating room stat is very good with weather comp and auto enabled.

Jaysus I may take a closer look at the veismann. That 4 pipe system sounds like it's the dogs bollocks altogether

shane 007

Dtp1979 wrote: »

Jaysus I may take a closer look at the veismann. That 4 pipe system sounds like it's the dogs bollocks altogether

Make sure your pockets are lined & deep.

Dtp1979

shane 007 wrote: »

Make sure your pockets are lined & deep.

Ya. Maybe I'll stick to my aristons

JohnnieK

Dtp1979 wrote: »

Ya. Maybe I'll stick to my aristons

Always good to give the option.

I go in with the two and let the customer decide.

Dtp1979

Dtp1979 wrote: »

Ya. Maybe I'll stick to my aristons

There are times when a Viessman will serve you better than a traditional boiler irrespective of the price.

It's good to have options as John mentioned, you may want to use a w-plan which is designed to give better hot water performance or fit a four pipe system which is more suited to plumbers as there is less wiring and more shiny pipes.

Listening to the customers needs and then having a wider range of options leads to happy customers.

I'm coming across a few installs where the installer has decided what their customer is right for their customer bypassing the listening stage, this has led to unhappy customers.

Personally I don't like the funky extras Shane has mentioned (unless it's a new full system)as a boiler striving for efficiency and programmed by a person assuming a well designed heating system does not cope well in a badly designed heating system, so the technology becomes a hinderance.

AstraMonti

shane 007 wrote: »

No, not at all. Keep the TRV's along with good controls. Just remember to remove the TRV heads where there is a room thermostat in the same room/area as they will conflict.

Really? That's very interesting to read. Is that the same for all TRV or only for the "smarter" models?

JohnnieK

AstraMonti wrote: »

Really? That's very interesting to read. Is that the same for all TRV or only for the "smarter" models?

The same for all trv's.

A room stat and a trv will conflict with each other as mentioned.

The room stat controls the zone the trv controls the room. If the trv shut the radiator down before the room stat that zone could in essence never shut down during the heating period.

You can get smart trvs that turn each room into a zone and communicate wireless with the boiler. In this case you would not have a room stat.

AstraMonti

Thanks very much for that. So to ask a practical question, if I have the TRV valve in no3 (half way) and the thermostat in the other wall at 20C, when will the radiator stop getting hot?

JohnnieK

AstraMonti wrote: »

Thanks very much for that. So to ask a practical question, if I have the TRV valve in no3 (half way) and the thermostat in the other wall at 20C, when will the radiator stop getting hot?

At what ever no 3 is on the head. That no 3 usually is between 16/18 degrees so it will look for an air temp of that temperature before closing. Depending on some factors like quality of the valve and overhanging curtains you could get over shoot or under shoot.

AstraMonti

Right thank you, I am just trying to understand how it really works then. All my rads have TRV valves but I also have thermostats. Sometimes the rads go cold before reaching room temp (on the thermostat) and some other times they keep going beyond the thermostat.

ZV Yoda

We got the boiler sorted now, so it's working fine (needed to replace the expansion tank & valve).

I had another question: We'd like to be able to use the gas boiler to heat water only during the summer (we haven't done this previously). However, I've just found out that our summer valve only controls 11 of the 17 rads. I can't find any other valves to turn off the remaining 6.

We could in theory just shut off the 11 rads using the summer valve & the TRVs to shut off the remaining 6 rads. However, given the previous comments about "no boiler interlock", short cycling, efficiency etc, I was wondering if it would be worth our while getting a plumber to re-work the piping to ensure all 17 rads could be turned off using the summer valve? I've no idea how big a job this would be - hopefully all 6 rads come off one feed at some point in the system.