DIY Doctor

Is Radiator Balancing Really Necessary With TRVs Installed?

Postby KDM » Sun Dec 08, 2019 4:41 pm

Hi.
My home has Thermostatic Radiator Valves installed on all the radiators. the system hasn't been serviced in a while and I drained it down, filler it up with a flushing agent, drained it, flushed it with clean water and finally refilled it with an antioxidising agent.

One reason for doing this was that the radiators were not all heating up evenly, despite my best efforts to balance the system.

My question is a simple one: given that the rads have TRVs, is balancing even necessary?

Thanks.
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Postby ericmark » Mon Dec 09, 2019 1:51 am

Simple answer is yes, the lock shield valve setting is important, but would not call it balancing in the old way.

I found the problem with a TRV is they are slow to move, so the temperature will over shoot, I found with liquid and wax heads it was a problem setting the lock shield as you simply don't know what temperature they are set at, marked *123456 is useless, I want to set to 20°C, then putting a thermometer in the room one can open or close the lock shield until the target temperature and current temperature are the same, I was using electronic programmable heads so it was showing both target and current on the PC.

So I moved my electronic heads around the while setting the lock shield, then once set moved them back to main rooms.

With the TRV on the feed it's not too bad, but with the TRV on return it is very important to slow the heating of the radiator to a speed that the TRV can close fast enough not to over shoot.

Even without this consideration unless set it is hard to reheat the house, with a modulating boiler the output can vary between around 8 kW and 28 kW. If the lock shield valve is left wide open, then the water will heat the closest radiator first, the hot return water will close the boiler down to around minimum output, as the TRV closes it will then force water through the next radiator, and so on, once all rooms are warm then the boiler will allow full output, but until all rooms are warm, the boiler will not give full output.

In theory there is no need for a wall thermostat, however in practice without the wall thermostat as the weather warms up the boiler will continually cycle off/on, so the idea is to fit a wall thermostat in a entrance level room with no alternative heating and no outside door which is normally kept cool. However in real terms that room rarely exists.

So using the hall clearly it has an outside door, so you need both a TRV and wall thermostat in the same room (hall) which was always against the advice given before the modulating boiler.

So idea is the TRV is wide open after the door has been opened so reheats the room fast, but before it reaches the wall thermostat temperature the TRV starts to close, so extending the time required to reach the last degree or two.

This also presents a problem, as if you change the temperature on the wall thermostat, you also need to change the temperature on the TRV, I fitted a Nest gen 3 thermostat and an Energenie MiHome programmable TRV which should have worked together, so as I should have set Nest, and the TRV should have followed, however it seems Nest has removed support, so I have to manually set the same schedule on both devices, which means I have a £50 TRV head where a cheap £10 eQ-3 programmable head would do same job, but in real terms not set exactly the same anyway, the long hall means heat takes time to travel along it, so the TRV is set to lift temperature at 7 am, but the wall thermostat raises temperature 0.5°C per hour for 4 hours or it will over shoot, but mainly that's because my boiler in this house does not modulate as I am using oil.

So I have a wax TRV in shower room, no TRV in bathroom, 4 MiHome TRV heads in living room, dinning room and hall, and a eQ-3 head in kitchen as it has open window function so when I unload shopping it auto turns off heating.

Upstairs another 4 eQ-3 heads in my case the more expensive blue tooth versions at £15 each. Although I will admit once set I don't really use the blue tooth, I simply press the comfort/eco button to swap between 17°C and 20°C when I enter a room, and can also press the boost button if I want a fast warm up.

So if you maintain your house at the same temperature day and night and never turn off heating in winter you could get away without setting the lock shield valve, but if you change temperature through the day, then the lock shield needs setting.
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Postby KDM » Mon Dec 09, 2019 2:37 pm

OKay, I switch the heating off for a couple of hours, and let it cool. Then I opened up the TRVs (except one I forgot) switched it on and estimated which rads heated up the quickest. I turned the two very hot ones down a quarter on the lockshields, then the next 3 down a little nudge (there are 12 rads in my house).

I don't have electronic heads, but the manufacturer's label suggests that setting "3" equates to 20 degrees, which works for me in all the occupied rooms.

There must be an airlock or something. Three rads took nearly an hour to warm up and two others didn't warn up at all. The two which didn't warm up are both above the floor, so I can feel the bypasss pipe and it is also cold.

I don't know about slow to move, but certainly, when my TRVs open, it does take long time for the rad to warm up. With the exception of two, all my TRVs seem to be on the return. Based on your suggestion, that probably explains the lag! they are all reversible, so that can be fixed. Most of them seem to have been placed for convenience. Nevertheless, I'd just as soon not drain the bugger down again this winter! I've already dedicated 3 days holiday, and very nearly a divorce to the project!

I didn't fully grasp the rationale behind the idea that the fully open rad will return HW to the boiler, causing it to shut off. I had supposed that the "out" from the first radiator sent to the next, etc. I made some temperature probe clips and my gas boiler is happily modulating between 56 degC and 68 degC about every 10 minutes with the return temp following it between 60 and 68.

My wall stat is in the landing, which is always about 2 degrees warmer than the hall. That's probably because it's right above the hall radiator, which is the biggest one in the house and the kids are crap at closing doors. In fairness, that stat hardly every kicks in, except late in the evening.

Ha ha, yes, I have mused like yourself about the nonexistent room with nonexistent radiator on the ground floor with nonexistent external doors!

I do switch the heating off during the day. At this time of year anyway. The house mostly heats up in a few hours.

I have been tempted to fit electronic heads in a few rooms. The bedroom and the bathroom both regularly get the window left open while the heating's on full tilt. My house is getting "smarter" but it's mostly my own innovation. I have room temperature /humidity probes in four locations around the house, but my favourite is the 6 temperature probes I have on my hot water tank. This was in order to answer the question "how much hot water is there?" I can see that there's a very definite halocline in my tank. If I assume that "hot" is 47 degrees, I can see where in the tank the hot water meets the cold. It seems fairly accurate.

Right, two hours in, and the last rad in the back hall has suddenly warmed up, very quickly. It has a TRV, but it has NO HEAD. The previous owner has panelled the wall, so that here is no clearance to fit a head. So I guess it's full open, but I can't understand why it, nor its bypass pipe got hot until just now. Since the return to the boiler hasn't dropped below 52 all morning, I can't see why this rad is oddball. It must be an airlock somewhere.

Thanks for the tips.
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Postby ericmark » Tue Dec 10, 2019 6:04 pm

I adjusted the lock shield the reverse to you, turned fully off, then slowly bit at a time back on until pipe got warm.

Modulating boilers are controlled by return water, so if we consider all TRV and wide open lock shield all radiators in parallel then boiler heats up closest radiator, which sends hot water back to boiler so boiler modulates (turns down) then as room warms up it heats the next radiator.

Once all warm the TRV will work A1, it is only while heating that this happens.

As to electronic heads, the eQ-3 starts at around £10 although I use the more expensive blue tooth version. But at that price may as well program each room.
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Postby KDM » Sat Dec 14, 2019 9:19 pm

Ah, the penny drops. Thank you, again.
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