Are new radiators more efficient?

bernardgreen said:

One could say that if the water leaving the radiator is still hot ( hotter than the air in the room ) then the radiator was not efficient at transferring heat from the water to the air in the room

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I see your point, so should the pump continue until return water is cold?

My understanding is the lock shield valve is set to allow a set drop in temperature between incoming and outgoing water, since I can't find my differential thermometer I can't really set my radiators that way, I look to ensure current does not exceed target with each room, which should only happen if there is too much flow causing a hysteresis.

But seem to remember something about calculating Δt° is the difference, so there are really two Δt° one between incoming and out going Δt° of the water, and one average radiator temperature and room temperature Δt° of the air. But this does not take into account the heat radiated by the pipes, I will not say lost, as I quite like the warm floor in our toilet/shower room, and in most cases heat radiated from pipe work does get into the home.

There is a calculation to match the advertised output of the radiator to actual output of the radiator by correcting the Δt° used in the advert to the Δt° of the home. But this must be at best a aid to selecting radiator size, as in the real home some thing will alter air flow.

This looks grand, but in three dimensional homes, some thing some where will interrupt that flow. This was the problem with my first house and hot air heating, the fans ensured even with furniture the air was circulated, although at first glance that may seem good, what it did was remove the cold air from next to the windows so more heat passed through the single glazed windows.

We get this problem, and the debate as to if a radiator should be on an outside wall or internal wall has gone on for years, well before central heating became the norm.

The solid fuel fire needed combustion air, placing it on the outside wall means combustion air can be drawn easy from outside, so with vents near the fire drafts were reduced, but in the centre of the house, less heat lost through walls, but needed high backed chairs to stop the draft unless ducting was fitted for the combustion air.

The problem is homes have changed, with double glazing and cavity wall insulation, and loft insulation and outside doors with good seals and drafts have been excluded from our homes, which also means natural air circulation.

Heat recovery units may help, but we must not forget many homes still have the option of using solid fuel, there are room sealed stoves with external air supply, but not very common. So we have to be careful with anything blowing air outside, be it a cooker hood, tumble drier, or bathroom extractor, we don't want exhaust gases being drawn into the home.

Lucky the plumber doing my shower blocked up the vent to outside, I say lucky as bees made a nest in the air brick last year, had it not been blocked up likely would have had bees in the house.

But there must be some hot water in the boiler and pipe work when the boiler switches off, and some of that heat must go outside, but with an oil boiler i.e. not modulating the heat retained in the radiators reduces the hysteresis, so the old iron radiator which held more water is likely better.

As to a modulating boiler not so sure, until the boiler reaches its lowest output it should not turn off, the TRV in each room allows just enough heat for that room, and radiators may only be at 40°C which can be a huge advantage as I found with mothers house, where sun through bay window could cause living room to over heat, so the less heat stored in the radiator the better, the more like a motor vehicle radiator they are the better, reverse to oil boiler.

Once I used the TRV to control room temperature the morning sun stopped heating room to 32°C when set to 20°C but only hit 24°C, even without a radiator the room would have likely over heated, but wanted the radiator to store as little heat as possible, so as quickly as possible when the sun came out the radiator went cold.

The big problem is getting the TRV set up to start with, and tradition was to set temperature with a wall thermostat, we still need a wall thermostat with a modulating boiler to turn off the system on warm days, mothers house there were two, one in kitchen and one in hall, so if wind caused one side of house to be cold, one would ensure heating stayed on, but the big improvement in that house was putting a TRV in the hall as well, so hall could quickly re-warm when front door opened, but not switch boiler off permanently as the TRV slowed flow rate before wall thermostat set temperature reached.

A modulating boiler should not switch off until fully modulated, the problem was there was nothing on that boiler to tell you what the output was.

All that really matters and is important, is the area of steel exposed to the rising air convection flow. Modern steel pressing and production methods can squeeze more area of steel into a smaller space, along with better design. However radiators 40 years old will be sized for a greater heatloss from the home and if like many - you have improved the the insulation over the years, the heat capacity of the rads will be more than enough.

My own 40 year old rads were installed when this place had draughty SG, leaky doors, no insulation in the cavity, minimal insulation in the loft, two windows even had plastic wind driven air vents and several rooms had through the cavity air vents - all heated by a 28kw boiler. Comfortably warm it never ever got when it was really cold outside and boiler even had to run during the night sometimes, to restore the lost heat.

Having addressed all of those things now, adding proper designed in ventilation boiler has been downsized to 18Kw, stat is set overnight to 16C and is never called to run during the night, ever, even when it is a sub-zero night. Except when the stat is suddenly turned up, the radiators tend to be no more than lukewarm and boiler showing return at 40C.

I am not convinced by Ian's suggestion that painting the rads makes that much difference to their ability to conduct heat, or their general efficiency.

For interest, I maintain and have maintained a 1 minute interval log of weather, indoor and outdoor temperatures, indoor and outdoor humidity etc.. What I would like to add, but so far have been unable to, is to add a gas consumption log.

So really, the only valid reason to change my rads would be for cosmetic reasons, or if they developed leaks. I maintain everything properly, myself, so leaks are unlikely.

ericmark said:

The solid fuel fire needed combustion air, placing it on the outside wall means combustion air can be drawn easy from outside,

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One system I came across, drew it's combustion air from below the floor - sometimes a cellar, sometimes a simply the space below a wooden floor above the dirt.

ericmark said:

I see your point, so should the pump continue until return water is cold?

My understanding is the lock shield valve is set to allow a set drop in temperature between incoming and outgoing water, since I can't find my differential thermometer I can't really set my radiators that way, I look to ensure current does not exceed target with each room, which should only happen if there is too much flow causing a hysteresis.

But seem to remember something about calculating

Δt° is the difference, so there are really two Δt° one between incoming and out going Δt° of the water, and one average radiator temperature and room temperature Δt° of the air. But this does not take into account the heat radiated by the pipes, I will not say lost, as I quite like the warm floor in our toilet/shower room, and in most cases heat radiated from pipe work does get into the home.

There is a calculation to match the advertised output of the radiator to actual output of the radiator by correcting the Δt° used in the advert to the Δt° of the home. But this must be at best a aid to selecting radiator size, as in the real home some thing will alter air flow.

This View attachment 258441 looks grand, but in three dimensional homes, some thing some where will interrupt that flow. This was the problem with my first house and hot air heating, the fans ensured even with furniture the air was circulated, although at first glance that may seem good, what it did was remove the cold air from next to the windows so more heat passed through the single glazed windows.

We get View attachment 258442 this problem, and the debate as to if a radiator should be on an outside wall or internal wall has gone on for years, well before central heating became the norm.

The solid fuel fire needed combustion air, placing it on the outside wall means combustion air can be drawn easy from outside, so with vents near the fire drafts were reduced, but in the centre of the house, less heat lost through walls, but needed high backed chairs View attachment 258443 to stop the draft unless ducting was fitted for the combustion air.

The problem is homes have changed, with double glazing and cavity wall insulation, and loft insulation and outside doors with good seals and drafts have been excluded from our homes, which also means natural air circulation.

Heat recovery units may help, but we must not forget many homes still have the option of using solid fuel, there are View attachment 258444 room sealed stoves with external air supply, but not very common. So we have to be careful with anything blowing air outside, be it a cooker hood, tumble drier, or bathroom extractor, we don't want exhaust gases being drawn into the home.

Lucky the plumber doing my shower blocked up the vent to outside, I say lucky as bees made a nest in the air brick last year, had it not been blocked up likely would have had bees in the house.

But there must be some hot water in the boiler and pipe work when the boiler switches off, and some of that heat must go outside, but with an oil boiler i.e. not modulating the heat retained in the radiators reduces the hysteresis, so the old iron radiator which held more water is likely better.

As to a modulating boiler not so sure, until the boiler reaches its lowest output it should not turn off, the TRV in each room allows just enough heat for that room, and radiators may only be at 40°C which can be a huge advantage as I found with mothers house, where sun through bay window could cause living room to over heat, so the less heat stored in the radiator the better, the more like a motor vehicle radiator they are the better, reverse to oil boiler.

Once I used the TRV to control room temperature the morning sun stopped heating room to 32°C when set to 20°C but only hit 24°C, even without a radiator the room would have likely over heated, but wanted the radiator to store as little heat as possible, so as quickly as possible when the sun came out the radiator went cold.

The big problem is getting the TRV set up to start with, and tradition was to set temperature with a wall thermostat, we still need a wall thermostat with a modulating boiler to turn off the system on warm days, mothers house there were two, one in kitchen and one in hall, so if wind caused one side of house to be cold, one would ensure heating stayed on, but the big improvement in that house was putting a TRV in the hall as well, so hall could quickly re-warm when front door opened, but not switch boiler off permanently as the TRV slowed flow rate before wall thermostat set temperature reached.

A modulating boiler should not switch off until fully modulated, the problem was there was nothing on that boiler to tell you what the output was.

Click to expand...

As you’ve put some thought into this, let me try this on you! I don’t think outdoor weather compensation, which is intended to improve efficiency by giving lower boiler return temperature hence more condensation, does much good.

Take a system like mine, 15kW boiler, and assume it would be firing continuously when outside temperature is -10°C, inside 20°, and when dissipating 15kW the water temperature is 75° flow, 65° return, average 70°. So ΔT outside-room = 20 – (-10) = 30°, Δt rad-room = 70 – 20 = 50°.

When outside temperature is 0°C, ΔT = 20°, so assuming heat transfer is proportional to ΔT, demand = 20/30*15 = 10kW. So required Δt = 50*10/15 = 33.3°, and rad average = 20 + 33.3 = 53.3°, 58.3° flow, 48.3° return. With a modulating boiler that’s about where it would end up, without weather compensation telling it. Return low enough for condensation. Maybe not quite as good with an On/Off boiler like mine, but it will still stop on the room-stat before the water temperature is much higher. My boiler never goes off on the control-stat (in CH mode) and when the weather is moderate the rads only get lukewarm.

Of course the above figures are typical, for illustration, but what do you think?

Harry Bloomfield said:

I am not convinced by Ian's suggestion that painting the rads makes that much difference to their ability to conduct heat, or their general efficiency.

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Yes I was at collage when it was done, the head of the science department decided white radiators was not the right thing when teaching students mat black was a better colour, so had all the radiators in the science department painted mat black, result was science department toasty warm, however it upset the balance of the whole system, and other areas got rather cold, so by next year all white again.

fixitflav said:

weather compensation

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If you take a standard TRV and test it, you will find the gap between fully closed and fully open is large, so set at say 2.5 radiator has a range of 19°C to 23°C so still heating when weather is warm enough, using an electronic head the range is more like 0.5°C so the need for weather compensation changes between mechanical and electronic TRV heads.

We of course don't want to heat the house in the morning, when likely in the afternoon we will want the AC running, however sensors outside are unlikely to forecast what the temperature will be like latter, so to compensate we need a link to internet and some form of weather forecast.

I have already posted about the problems using internet, high winds last year took out the local EE mast for mobile phones, my heating used geofencing, so thought I was not at home, so turned heating to Eco setting.

Each home is different, there is no one size fits all. But I have gone to manual setting time, so in the morning the hall raises at 0.5°C per two hours, so by evening at 20°C and at around 11 pm drops to 16°C over night. This means the boiler runs all day, if I raised the temperature to 20°C first thing in the morning it would likely over shoot, however this was not the case with either my old house or mothers house, the problem is cooling not heating, the hall cools too slow, so over heat hall and boiler is then off for an extended time.

Be it sun in bay window, winds from the North, or outside doors in every ground floor room, each home is different, and we all tend to consider heating by looking at our own home.

fixitflav said:

As you’ve put some thought into this, let me try this on you! I don’t think outdoor weather compensation, which is intended to improve efficiency by giving lower boiler return temperature hence more condensation, does much good.

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They help the system to predict just how much heat input it needs to produce more precisely to help prevent over shoot and help keep the boiler below the condensation temperature threshold. I developed such a control back in the early 90's, using an 8085.

ericmark said:

Yes I was at collage when it was done, the head of the science department decided white radiators was not the right thing when teaching students mat black was a better colour, so had all the radiators in the science department painted mat black, result was science department toasty warm, however it upset the balance of the whole system, and other areas got rather cold, so by next year all white again.

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The colour does affect the radiation, but simply painting them white, when the existing colour is white will make very little difference to the emissivity. I do of course agree that painting them black will improve the emissivity of any hot surface - hence the reason that all heatsinks are painted matt black.

I think that the only reason radiators are not normally supplied in black, is that the colour would not be acceptable to the public.

Harry Bloomfield said:

I think that the only reason radiators are not normally supplied in black, is that the colour would not be acceptable to the public.

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All car radiators are normally supplied mat black, and so are the matrix inside fan assisted radiators in the home.

ericmark said:

sensors outside are unlikely to forecast what the temperature will be like latter, so to compensate we need a link to internet and some form of weather forecast.

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Whether or not weather compensation gives much benefit, I can't see how predicting future weather helps. Presumably if the forecast is for colder weather the boiler flow temperature is increased, but I'd have thought it's better to keep it as low as possible until it needs to rise, ie when the cold weather arrives. And you've got more faith in the Met Office than I have!

fixitflav said:

Whether or not weather compensation gives much benefit, I can't see how predicting future weather helps. Presumably if the forecast is for colder weather the boiler flow temperature is increased, but I'd have thought it's better to keep it as low as possible until it needs to rise, ie when the cold weather arrives. And you've got more faith in the Met Office than I have!

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You got the wrong idea... It uses the current temperature outdoors, plus an preset factor, as a means to determine how much heat the building is likely to need as input, to make the desired temperature. It avoids wasteful overshoot and allows it to neatly hit target, rather than blindly chucking heat out, until the stat says enough.

It's the difference between how some drivers tear up to red lights then bang the brakes on, wasting lots of fuel and those more capable drivers who see the lights are red in front and just take their foot off the loud pedal and trickle up with minimum use of brakes.

It has two benefits - a saving in gas, the boiler better able to run condensing and the house temperature is more stable, less under and over shoot of temperature.

Harry Bloomfield said:

plus an preset factor, as a means to determine how much heat the building is likely to need as input,

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"Is likely" is the point I'm making. That implies a prediction of future weather.

I have a basic system, room-stat and TRVs, and I don't get over- (or under-) shoots. Some people I know are forever adjusting their room-stat. I set mine at 20°C and don't touch it from one year's end to the next. I leave CH and HW live 24/7, I find it uses no more gas that way than On/Off on a timer.

fixitflav said:

I set mine at 20°C and don't touch it from one year's end to the next

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Sometimes my wife doesn’t touch the thermostat for a whole hour.

We have one of those magic thermostats; the higher it’s turned up, the faster the house heats up……..

Notch7 said:

Sometimes my wife doesn’t touch the thermostat for a whole hour.

We have one of those magic thermostats; the higher it’s turned up, the faster the house heats up……..

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Got them in the car as well.....

Harry Bloomfield said:

It avoids wasteful overshoot and allows it to neatly hit target, rather than blindly chucking heat out, until the stat says enough.

Click to expand...

Since moving to electronic TRV heads not had much of a problem with over shoot, if anything the reverse, my Energenie MiHome heads seem to have OTT anti-hysteresis software, set from 16°C to 20°C at 7 am, and still not hit 20°C by 10:30 am.

Notch7 said:

We have one of those magic thermostats; the higher it’s turned up, the faster the house heats up……..

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Yes it does work, with the Energenie heads turn it to 22°C at 7 am and 20°C at 8 am and it was at 20°C by 8 am. So we have to counter the built in anti-hysteresis software.

I read that the Wiser TRV head actually works out the time taken to heat a room, and the built in algorithms remove the problems found with my Energenie TRV heads.

Nest did work by the wall thermostat telling the TRV what temperature was required, now support removed so does that no longer, but every other linked TRV and wall thermostat seems to work other way around, the TRV tells the wall thermostat or hub when heat is required.

So since the TRV controls room temperature (not the wall thermostat) then to have weather compensation this needs linking to the TRV not the wall thermostat or boiler.

More to point the only reason to reduce heating due to weather conditions is when sun latter in the day is likely to heat the home to a point where we need cooling, and we are prepared to be a little cool in the morning so we do not roast latter in the day, by the time in the year that is likely to happen, I have turned off my central heating. So having weather compensation is simply pointless.

I think 4 out of 9 of my TRV heads can use IFTTT and can be programmed to work with geofencing, and weather compensation, but those 4 have such a OTT anti-hysteresis I would never bother.

ericmark said:

I have already posted about the problems using internet, high winds last year took out the local EE mast for mobile phones, my heating used geofencing, so thought I was not at home, so turned heating to Eco setting.

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I'm not laughing at your misfortune but the story did make me smile.