over sizing radiators

thebandit said:
Just a comment on the oversizing of rads, I scan read through and don't believe anyone has mentioned the fundimental ... balancing. Minimum rad size is important, maximum not so much. Bascially you need a rad sized at least big enough to heat the room, if its bigger than the recommended its no issue. The most important thing to do with the heating system is balance the radiators correctly. This is what ensures all rooms heat well and the return to the boiler is low so it condenses and runs efficiently. There are loads of guides across the internet but basically you have to start at the first rad on the circuit, with the thermostatic valve fully open (removed ideally) , adjust the lockshield until you get ~12 - 18°c drop across the flow and return pipe on the rad. Move along the rads in the heating circuit until you have done all of them. You'll be surpirsed how little the lockshield needs to be open on the first rads in the circuit, often only a quater of a turn from fully closed. So many people have no clue about this, they think having everything fully open will be better, but whats happening in the background is the first rad with a fully open lockshield is pushing very hot water straight back to the boiler preventing it condensing and also stealing heat from the rads further along the heating circuit.
Click to expand...
The thing is, it just seems like such a dark art. I was actually intending to balance my rads just as COVID happened and those infrared thermometers went to crazy prices :cry: :cry:

I am interested in those autobalancing valves that @danlightbulb linked to. I can't get my head around how they work though!
 
thebandit said:
Just a comment on the oversizing of rads, I scan read through and don't believe anyone has mentioned the fundimental ... balancing. Minimum rad size is important, maximum not so much. Bascially you need a rad sized at least big enough to heat the room, if its bigger than the recommended its no issue. The most important thing to do with the heating system is balance the radiators correctly. This is what ensures all rooms heat well and the return to the boiler is low so it condenses and runs efficiently. There are loads of guides across the internet but basically you have to start at the first rad on the circuit, with the thermostatic valve fully open (removed ideally) , adjust the lockshield until you get ~12 - 18°c drop across the flow and return pipe on the rad. Move along the rads in the heating circuit until you have done all of them. You'll be surpirsed how little the lockshield needs to be open on the first rads in the circuit, often only a quater of a turn from fully closed. So many people have no clue about this, they think having everything fully open will be better, but whats happening in the background is the first rad with a fully open lockshield is pushing very hot water straight back to the boiler preventing it condensing and also stealing heat from the rads further along the heating circuit.
Click to expand...
You can't do that with modern systems though.
 
dlockers said:
The thing is, it just seems like such a dark art. I was actually intending to balance my rads just as COVID happened and those infrared thermometers went to crazy prices :cry: :cry:

I am interested in those autobalancing valves that @danlightbulb linked to. I can't get my head around how they work though!
Click to expand...

You really need a thermocouple temp sensor tbh, I have tried before with those infa red thermometers and the reading is unreliable on the pipes. The other thing is, it often takes a few sessions running from cold to hot to get the balance right, you need to do it in sets of rads, the hardest part is working out which ones are actually where on the heating circuit, its certainly a bit of an art.

Re the "balancing TRVs"... well, that has sent me down a little rabbit hole too. Seems they have their place, but they are not a one size fits all solution to balancing, this video is quite good explaining. https://www.youtube.com/watch?v=0iowNpxyHqk&t=259s

THe only way I can think that true autobalancing would occur is if the TRVs also communicated with each other. Trouble with modern heating is there are various controls in seperate parts of the system working against each other, really it all needs to be in a unified system to be truely set and forget.
 
Last edited:
thebandit said:
You really need a thermocouple temp sensor tbh, I have tried before with those infa red thermometers and the reading is unreliable on the pipes. The other thing is, it often takes a few sessions running from cold to hot to get the balance right, you need to do it in sets of rads, the hardest part is working out which ones are actually where on the heating circuit, its certainly a bit of an art.

Re the "balancing TRVs"... well, that has sent me down a little rabbit hole too. Seems they have their place, but they are not a one size fits all solution to balancing, this video is quite good explaining. https://www.youtube.com/watch?v=0iowNpxyHqk&t=259s

THe only way I can think that true autobalancing would occur is if the TRVs also communciated with each other. Trouble with modern heating is there are various controls in seperate parts of the system woorking against each other, really it all needs to be in a unified system to be truely set and forget.
Click to expand...
Evohome does it. Takes about a week but eventually it learns how much to open each valve.
Manual balancing wrecks it, just doesn't work as you never know the flow, or which radiator/s will be on and by how much.
These auto balcony valves add a slight improvement but not much.
 
thebandit said:
Not sure why not ? not saying you aren't right, but I don't understand why, whats the issue ?
Click to expand...
How can you balance a system that is constantly changing.
Where would you start?
Turn every radiator on and balance. Then what when only one radiator is on, or two, what flow temperature 70c or 25c your not going to get a 20c drop at 25c flow.

I tried you just get rooms not warming up fast enough or overshooting.

Evohome for instance if one radiator is on it'll open a bit say 5% if another radiator comes on it'll open it to 10% and the new one to maybe 20% it learns how fast each room delivers heat and from there calculates how much to open each valve.

"ADVANCED
LOAD SCALING
evohome automatically learns
each zone’s heat capacity to
better control the boiler’s output.
It will limit inefficient high return
temperatures and keep the boiler at
its lowest possible rate."

I imagine other smart systems do similar.
 
Last edited:
-Ad- said:
What's the calculated heat loss of the house for winter design temp? This is what matters.

Unless you have them heating a swimming pool or huge annex, then it's either a country manor or has the the most un-insulated construction.
Click to expand...
7beds 4 bath secondary circulation and 6000sqft
But you made the assumption that it was crazy without knowing any of that.
 
jpaul said:
a heatpump delta t discussion -
discussing that it needs to be small to help heat-pump efficiency giving an even heat transfer inside its heat exchanger, so need a sufficiently high flow/pump rate to do that
point about modern radiators producing more even heat distribution (baffling ...) across radiator surface is interesting

Click to expand...

Wow. Terrible for system efficiency and demands high flow rates. Is he proposing a 2 degree dT?!
 
thebandit said:
You really need a thermocouple temp sensor tbh, I have tried before with those infa red thermometers and the reading is unreliable on the pipes. The other thing is, it often takes a few sessions running from cold to hot to get the balance right, you need to do it in sets of rads, the hardest part is working out which ones are actually where on the heating circuit, its certainly a bit of an art.

Re the "balancing TRVs"... well, that has sent me down a little rabbit hole too. Seems they have their place, but they are not a one size fits all solution to balancing, this video is quite good explaining. https://www.youtube.com/watch?v=0iowNpxyHqk&t=259s

THe only way I can think that true autobalancing would occur is if the TRVs also communicated with each other. Trouble with modern heating is there are various controls in seperate parts of the system working against each other, really it all needs to be in a unified system to be truely set and forget.
Click to expand...

The Danfoss version integrates a DPCV into the TRV. I don't think the type he's talking about have this. They don't need to communicate with each other.
 
mattyg said:
7beds 4 bath secondary circulation and 6000sqft
But you made the assumption that it was crazy without knowing any of that.
Click to expand...

Until you post what the heat loss calcs show for your house at a winter design temp of say -3degsC, then you can't say they aren't crazy oversized ;)
 
dirtychinchilla said:
Wow. Terrible for system efficiency and demands high flow rates. Is he proposing a 2 degree dT?!
Click to expand...
still think some kind of home simulator would be great - if you could map out your pipe runs are and bounds on room heat loss.....

heat pump spec eg https://www.panasonicproclub.com/uploads/IE/catalogues/PIR_AQ_J_GEN_MONOBLOC_HP_20.pdf
www.manualslib.com

Standard System (Optional Pcb Not Connected); Advance System (Optional Pcb Connected) - Panasonic WH-MDC05J3E5 Service Manual [Page 40]

Panasonic WH-MDC05J3E5 Manual Online: standard system (optional pcb not connected), Advance System (Optional Pcb Connected). Mono Bloc Unit Water System Air Purge Valve Olp 2 Refrigerant System Th Water Outlet Heater: Od 9Kw Series: 3Kw 7.2 Advance System (Optional Pcb Connected)...
www.manualslib.com www.manualslib.com
don't obviously provide optimal dT data ? although latter has clear installation diagrams matching home install routing water through heating or water tank, that you'd expect
 
mattyg said:
Why do I have 2 big 30KW boilers in my house? Its a big house but lets assume it was a small house with 1 30KW boiler but every radiator was twice the size and the same number, But the heat loss the same..... Would I need the 2nd boiler

And how does a boiler drop the flow temperature. Surely a boiler adds heat.
Isn't it the Radiators that take the heat out of the water, Usually about 10degrees if I remember.
Click to expand...
Lower flow temperatures are enabled by larger radiators. A lower flow temperature means the boiler uses less gas to heat your house. This is because the boiler stays in its condensing high efficiency mode for longer.

There is no such thing as a free lunch at the end of the day and it comes at the expense of slower response (E.g. it can’t heat up a cold house as quickly). The lower the flow temperature, the longer it takes.

Your heating system may be oversized but the margin for error on gas is huge and an oversized system will have lower performance but it’s not *THAT* much lower. It may not be oversized, but you’d have to run the calculations to check.
 
Last edited:
-Ad- said:
Until you post what the heat loss calcs show for your house at a winter design temp of say -3degsC, then you can't say they aren't crazy oversized ;)
Click to expand...
I absolutely can, Especially on the coldest days when we kick on the Wood burner too. But I do like my house warm.
The calcs were done about 8 years ago by 4 different firms with almost identical quotes. Where they are now I've no idea, And I'm not working out what 18 rooms are :D
 
Last edited:
jpaul said:
still think some kind of home simulator would be great - if you could map out your pipe runs are and bounds on room heat loss.....

heat pump spec eg https://www.panasonicproclub.com/uploads/IE/catalogues/PIR_AQ_J_GEN_MONOBLOC_HP_20.pdf
www.manualslib.com

Standard System (Optional Pcb Not Connected); Advance System (Optional Pcb Connected) - Panasonic WH-MDC05J3E5 Service Manual [Page 40]

Panasonic WH-MDC05J3E5 Manual Online: standard system (optional pcb not connected), Advance System (Optional Pcb Connected). Mono Bloc Unit Water System Air Purge Valve Olp 2 Refrigerant System Th Water Outlet Heater: Od 9Kw Series: 3Kw 7.2 Advance System (Optional Pcb Connected)...
www.manualslib.com www.manualslib.com
don't obviously provide optimal dT data ? although latter has clear installation diagrams matching home install routing water through heating or water tank, that you'd expect
Click to expand...

OK one example - flow rates.

first one is dT of 5K, second one is dT of 30K. Upping the dT by a factor of 6 reduces the flow rate by a factor of 6. If you link that to the pump affinity curve, that massively drops the pumping energy required.

AStRB3b.png



Another, thermal storage capacity. If you had, for example, 1000 L of thermal storage. At a dT of 5K, you would have a heat capacity of 6 kW. With a dT a factor of 6 bigger, at 30K, you have a thermal storage capacity of 36 kW.

Now, if you can generate that with a heat pump with an SCOP of 3.2, and you can combine that with solar panels or an off peak tariff, you can get a huge amount of thermal energy either free, or 6 times cheaper.
 
jpaul said:
still think some kind of home simulator would be great - if you could map out your pipe runs are and bounds on room heat loss.....
Click to expand...
100%. I have no idea how to even get started, so I just don't. I have all my lock shields open 100% and a flow temp of 50*Cs. It seems to work.
 
^^ with the lockshields all fully open like that I very much doubt your boiler is condensing and hence will running at sub optimum efficiency. Either way you still get warm but you are probably paying more for it.
 
dirtychinchilla said:
How are you controlling the flow if you have your lockshields 100% open?
Click to expand...
I have no idea because it seems those who understand heating systems are not those who are able to effectively communicate how to do the job to the masses :cry:.

I'd happily pay a grown up to come and balance my system, but they just don't seem to exist.

thebandit said:
^^ with the lockshields all fully open like that I very much doubt your boiler is condensing and hence will running at sub optimum efficiency. Either way you still get warm but you are probably paying more for it.
Click to expand...
If my bill can reduce from £2.60/day for 2.5hrs of heating + 180l of hot water I am all ears. Monday was 5hrs of heating + 180l of hot water for £3.63.

Always open to hear how I can save money though. Maybe I am looking in the wrong place, but mathematical formulas about Delta T aren't practical next steps for a normal human to follow!
 
dlockers said:
I have no idea because it seems those who understand heating systems are not those who are able to effectively communicate how to do the job to the masses :cry:.

I'd happily pay a grown up to come and balance my system, but they just don't seem to exist.
Click to expand...

That's because most plumbers aren't interested in efficient systems. That's not to say all arent, but many aren't.

What we advise, and what I did at home, is to close the lockshields and then open them up by a quarter turn at a time. I did this until they were heating up properly, but it was just slightly beyond the point of them not getting any heat into them. This simulates what an automatic balancing valve would do i.e. restrict the flow.

What you would ideally do is get a clamp on temperature sensor, or if you have a thermal gun or camera that would be good. Then, close the lockshield as I said above, and then open it until you're showing a decent dT (maybe 20K?) between flow and return on each rad.

Unfortunately 1, radiators without proper automatic balancing valves are destined to fail because the whole system falls apart as soon as one radiator closes and the pressure is distributed around the system.

Unfortunately 2, lockshield valves are dreadful. They have a flat valve seat, which means that they do almost nothing until they're virtually shut. A conical valve seat gives massively better control, which is one part of the automatic balancing valves that we sell - https://www.sav-systems.com/products/pt40-pi-trv/
 
You must log in or register to reply here.
Back
Top Bottom