Lower Flow Temperature & Higher Radiator Temperature?

[desktop987456]

The easiest way is to just decrease the temperature setting of the TRV, but as stated above at the expense of a colder room, its not much fun having a return temperature of 27C but a cold room. You could also let the TRV setting as is and set the flow temperature to say 70C and let the TRV act as a on/off control but apart from probably getting room temperature overshoot/undershoot you will still use more gas as the rad demand is higher.

but that would defeat the purpose of heating, wouldn't it?

What would happen if we oversize the rad but keep the flow rate at 50?

 

[berty3000]

So just to be clear, my heating system has to be in condensing mode if the flow rate is 50C, since the return temperature will be below 50?

Anything below 53C return temperature will mean condensing?

Would reducing the TRV settings reduce the return temperature when it means hot water from the boiler is being rejected? Note that my thermostat is in a colder room with a radiator that has no TRV, so they are what is driving the boiler.

Also, does it matter if my TRVs are on the return pipe as they appear to be?

 

[monkeysballs]

Trvs don't affect return temp unless they are fully closed then thd pressure increases in the remaining open rads then mord water goes through them. It is the lockshield that restricts water flow through the rad and most do that very badly!

 

[berty3000]

Trvs don't affect return temp unless they are fully closed then thd pressure increases in the remaining open rads then mord water goes through them. It is the lockshield that restricts water flow through the rad and most do that very badly!

Surely the TRVs restrict flow as well, otherwise how could they regulate the temperature of the radiator?

 

[monkeysballs]

As I said they only affect flow when they close and that is when they get to the temp you have specified by the setting at the top. non smart trv's don't really do partially closed

There are special trv valve bodies that are are pre-setable and with those you can specify the flow in litres per hour that it will allow to flow meaning you don't use the lockshield valve you just leave it fully open then the trv shuts it dow when the temp in the room goes above what you want


Trv's are to stop rooms going over temp nothing more really (unless they are smart ones that can actually call for heat)

 

[berty3000]

I've been measuring the temperatures at different radiators.

Boiler set to 50 although the stated temperature at the boiler is a bit below or above this at times.

The radiator without a TRV is in the room with the thermostat. One side measured up to 49C whilst the other side was about 43C.

In another room, the TRV is set to 5. One side is 48C and the other just over 43C.

I am happy with the termperatures in these rooms (19.5-21). Other than putting the TRV down to 3 so the radiator closes off at about 20C, is there anything I ought to change? Is my boiler being used efficiently?

Also, am I right in saying that for any given heating cycle, when some radiators close off the valves when TRV temperature is reached, that the other radiators get extra heat to devoted to them?

 

[monkeysballs]

Sort of they get more flow and because the return temp is higher the flow temp increases so then yes the water going into the rad is hotter so then the return is hotter so the flow is hotter and around you go untill the boiler says this water is too hot and shuts down

Really you don't want any rads shut down! You just need the correct temp and volume of water going through each rad to get to then maintain your desired room temperature

I mean I have no trv's I control my room temp by increasing and decreasing my flow temp based on the outside temp

As my radiators have been sized to give out the specific amount of energy my room requires at -3 outside temp and with maths you know how much is required all the way from there to what ever temp it is

 

[Johntheo5]

I've been measuring the temperatures at different radiators.

Boiler set to 50 although the stated temperature at the boiler is a bit below or above this at times.

The radiator without a TRV is in the room with the thermostat. One side measured up to 49C whilst the other side was about 43C.

The mean rad temperature is 46C

In another room, the TRV is set to 5. One side is 48C and the other just over 43C.

TRV setting of 5 means its wide open, see below, I set mine to ~ 2.5 to 2.8ish to maintain 20C room temp

I am happy with the termperatures in these rooms (19.5-21). Other than putting the TRV down to 3 so the radiator closes off at about 20C, is there anything I ought to change? Is my boiler being used efficiently?

Yes, of course there is, to maintain the same heat output from this rad with enhanced condensing, increase the boiler temperature to 64C and set your TRV appropriately, this will result in the same mean rad temperature of 46C, with flow/return temps of 64/28C, (64+28)/2=46. (simple maths)

Also, am I right in saying that for any given heating cycle, when some radiators close off the valves when TRV temperature is reached, that the other radiators get extra heat to devoted to them?

Yes, marginally, if the flow through your non TRVd increased by 10% then its output would increasy by ~ 2%, the room temp would increase by ~1C and the return temp would be ~ 31C.

 

[berty3000]

The mean rad temperature is 46C

TRV setting of 5 means its wide open, see below, I set mine to ~ 2.5 to 2.8ish to maintain 20C room temp

Yes, of course there is, to maintain the same heat output from this rad with enhanced condensing, increase the boiler temperature to 64C and set your TRV appropriately, this will result in the same mean rad temperature of 46C, with flow/return temps of 64/28C, (64+28)/2=46. (simple maths)

Why would the mean radiator temperature stay the same if the flow temperature has been significantly increased?

Also, at what point are the benefits of increased condensing outweighed by the higher burning of gas?

I read earlier that the return temperature should be 12C lower than the input temperature at the radiators, and to adjust the lockshields if this not the case. As there only seems to be 5 or 6C difference in my radiators, is there merit in tightening the lockshields a bit? Or is this to do with something different?

 

[Johntheo5]

Why would the mean radiator temperature stay the same if the flow temperature has been significantly increased?
The TRV throttling down the flowrate but still maintaining the desired room temp.

Also, at what point are the benefits of increased condensing outweighed by the higher burning of gas?
If all room rads are controlled then the gas consumption will be less.

I read earlier that the return temperature should be 12C lower than the input temperature at the radiators, and to adjust the lockshields if this not the case. As there only seems to be 5 or 6C difference in my radiators, is there merit in tightening the lockshields a bit? Or is this to do with something differen

12c is a bit meaningless IMO, maybe useful for balancing.
Adjusting lockshields?, as above

 

[berty3000]

Didn't you refer to adjustment of TRVs rather than lockshields?

All the TRVs are doing is cutting off the supply once a certain temperature is reached. From what I understand, adjusting the opposite valve will have a bearing on the return temperature.

At the moment there is only about 5C difference between flow and return temps at my radiators and this sometimes reduces to nothing. Makes no difference what setting the TRV is at.

 

[Harry Bloomfield]

All the TRVs are doing is cutting off the supply once a certain temperature is reached. From what I understand, adjusting the opposite valve will have a bearing on the return temperature.

The slower the water passes through your rad/the less the quantity - the cooler is will be by the time it gets to the return.

 

[Johntheo5]

Didn't you refer to adjustment of TRVs rather than lockshields?

YES.

All the TRVs are doing is cutting off the supply once a certain temperature is reached. From what I understand, adjusting the opposite valve will have a bearing on the return temperature.

Don't know where you got that information from, TRVs are proportional controllers with a very small hysteresis of ~ 2C, so as I pointed out before, as long as they are not fully shut before the rad return temperature falls to the room temperature then they control quite well, at least mine do in the 30+ years I'm using them.

At the moment there is only about 5C difference between flow and return temps at my radiators and this sometimes reduces to nothing. Makes no difference what setting the TRV is at.

I can only suggest they are not working properly, if the boiler is under any other form of control ie one room with a on/off room stat that has a big hysteresis where the boiler is off for long periods then this will tend to cause the TRVs to operate in a on/off way but will/should give fairly reasonable room temperature control but as stated previously its vital that they are set up properly, I would think that yours, in that room you are talking about shoud be set around 2.5, then only adjust it + or - in 0.2 index increments, mine are set for years at the their same setting, as the days slowly get colder and colder in the autumn then the rads will start just barely lukewarm and gradually increase in temperature as the days march on.

 

[berty3000]

Ok, so what can I do to make the radiators release more of the heat going into them, thereby giving me more heat and reducing the return temp?

As I say, I'm only getting a 5C difference from in to out. This is whilst the boiler is burning away. When it takes a break, which it periodically does, them the in and out temperatures at radiators seem to equalise a bit. As mentioned before, all the rooms have TRVs apart from the one where the thermostat is and that radiator always seems to be the hottest.

How about the flow rate from the boiler? Could that be too high so that the water is being pushed through the radiators too quickly?

Would closing the lockshield a bit not help to keep more heat in the radiator?

 

[berty3000]

... also, is there a way to get the boiler to tell me what the general flow and return temps are for the system? This will save me arsing about with a food probe at the radiators.

And does Worcester greenstar i give me the ability to check and adjust the flow rate?