I've mentioned a 0.6 factor before, but not recently. It came out of the Ultraheat leaflet, for converting their quoted power outputs (can't recall the delta) down for 70/50 operation for use with condensing boilers.
I used an early Myson Java calculator. It significantly over-estimated the radiator sizes (Andy Hall thought it had wrong U-values, but I didn't investigate where the error was). It actually means I've been able to run the heating at 45/40 even when just below freezing outside and get significantly better boiler efficiency than is normally expected. I didn't actually use any Myson radiators, although on reflection I'm rather pleased with the effect of the error.
Yes, except 3 sets of fins - one on each panel. Think of it like a double panel radiator with a single panel radiator added on the front.
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are both Ultraheat Compact 6. The 6 means they have two extra connections into the bottom, and both these cases are using the bottom connections so there are no side valves/pipework. The Ultraheat Compact 4 are the same, but don't have the bottom entry connections, although when you order a 4, you seem to get a 6 if they have no 4's in that size already made up.
Basai also did triple panel radiators at the time, but no one seemed to stock them or be willing to order non-stock items. The Ultraheat came in a full range of heights and widths.
Unfortunately, Ultraheat has the most aweful webshite you ever saw. If they'd just put up a PDF of the leaflet they supply the plumbers merchants, that would be a big improvement over the broken flash.
If you're anywhere near Dunstable Beds, these came from Dunstable Heating Supplies in High Street North - they get them in same day if you call early enough, next day otherwise (well, this is going back several years, but they're still there). I believe the radiators are made in Leighton Buzzard, which is just up the road.
They are deeper, but they are also smaller, which is the reason for using them.
A few people have said in the past don't bother buying single panel radiators mail order, as they always get bent in transit. Doubles are inherently stronger. The Ultraheat ones came wrapped in multiple layers of strong bubble wrap (the solid plastic side was much thicker than normal bubblewrap). None had any dents, dings, or other marks.
So, if you are looking at rads specified at (say) 50 and you want to know the output at (say) 40, divide the published output by 0.798 and then multiply the result by 0.605
[Or swap division and multiplication if you're grossing up the heat losses rather than downrating the rads - you'll end up in the same place].
The calculation programs have many parameters which you can vary - and you get different results if you do vary them. These include:
Assumed outside temperature
U-values for each type of wall, window, floor, ceiling, etc.
Temperature in adjacent rooms
Number of air changes per hour
In addition, some programs build in extra allowances for transitional effects. To heat a room quickly, you need to input heat at a higher rate than you need to maintain a steady state when it's up to temperature. So you need to look at *all* of these things in order to make sure that you're comparing apples with apples.
I only read this after I had answered your previous post.
The 0.6 comes from converting from 60 to 40. All rads used to be quoted at
60, but most are now quoted at 50 - hence the difference.
If you divide all the figures I quoted by 0.798 - so as to get 1.000 at 50, then 60 gives 1.25 and 40 gives 0.758 - which are not a million miles away from the figures which you are now using.
Is there a big difference between the appearances of different makes? For standard radiators, they all seem to look the same: metal sheets enclosing each end and plastic grill on top. Or so it appears from the tiny photos on the various web sites.
Would I be right to say there is no problem if all the rads are oversized, provided they are all oversized by the same amount? I would think that if you have an oversized radiator, you can always turn it down but if you get an undersized radiator, you are stuck.
Thanks. I hadn't seen that before. The Stelrad pdf quoted in the wiki has a similar table but it has been revised for dT=50, I.e. the 50 C entry has a factor of 1.00, 60 C has a factor of 1.27, and 40 C has a factor of 0.75. It's worth having both tables because some merchants still quote outputs at dT=60 and others at dT=50. Using the "right" table I would only have to multiply once, rather than twice.
Yes, it is a real headache. It's easy enough to measure the rooms and the windows but it's not always possible to know how thick the walls are and what they are made of. I wonder how professional installers manage? I am sure they don't go asking what the ceiling, floor, and walls are made from!
I think I am only using half of the Barlo calculator's abilities. I have used it to calculate the heat losses. I notice it has the water temperature set to 60 C. Now if the room is 20C, that would mean dT=40. I think the programme can suggest the appropriate Barlo radiator. Can I save myself the calculations and get it to tell me what rads I need?
They use a very scientific instrument along the lines of a wet finger in the air!
dT is the difference between the room temperature and the *mean* radiator temperature - not the flow temperature. So, if your rads have a 10 degree drop (in at 60, out at 50) the mean temperature is 55, and dT is only 35.
The Barlo program (the version I have, anyway) is very old and doesn't reflect the current range of radiators available. I only us it for calculating the heat losses, and then do the match to individual radiators manually.
Pretty much - particulartly if they are fitted with TRVs. Provided you have sufficient boiler capacity, it will speed up getting the house up to temperature from cold. If you have one of two which are more oversized than the rest, you can always throttle them back a bit when you balance the system - setting their drop a bit higher than the rest to reduce their output and to make sure that they don't hog all the heat.
You do need to watch the rad in the room where the room stat is located, though. If that room heats up *too* quickly, the room stat will turn the boiler off before the other rooms are up to temperature.
I am glad I asked. I wasn't sure what it meant by water temperature. Flow temperature does seem the obvious choice but I wasn't sure whether it might have been mean temperature. After all, if the rads are balance, shouldn't the drop across the rad and the mean temp be the same for all rads? I will have to change it to 65 C. Thanks again.
Correct. If you have a condensing boiler, you can turn down the circulating water temperature, which increases boiler efficiency. That's what I've been able to do (particularly in my case as the boiler doesn't do the hot water, so it can be set way below normal hot water temperatures). Another benefit of low radiator temperatures is that the energy stored in a radiator is lower, and less likely to cause overshoot. Indeed, I have almost no overshoot on that system (less than 0.5C), without any need to actively control it, and so the room temperature changes by only 0.5C as the heating demand cycles on and off, as that's the hysterysis I deliberately include in the control system to prevent overly frequent demand cycling.
The only time I've had to set it above 45C is when I've been away for days and the house has cooled down to frost protection levels and it's minus something outside. Then I set it to 55C or 60C for an hour or two to quickly heat the house up. It can do it at 45C flow, but it takes many hours.
When I was commissioning the system, I tried running it at 83C (the boiler's max), but I couldn't get it quite there, as at that temperature the radiators would be giving off more power than the boiler's 25kW output. (Could have covered some up or turned them off, I suppose.)
A mixture of radiators mis-sized in different ways will always present problems. TRV's will help, but can't cure the problems. You can adjust the output slightly by misbalancing to create different average radiator temperatures, but again the control you'll have over this isn't going to cover up significant mis-sizing.
Thinking ahead to when I change my system boiler to a condensing one, Can any be set to deliver output at a higher temperature for hot water? I currently use mine at about 80deg to heat the hot water, and am considering a heatbank in order to get mains pressure hot water, and that again would require a higher temperature than is required solely for heating.
I suppose I could adopt DD's method of 2 combis, installing the plastic pipes with a hacksaw.
With Biasi, the grill on top (and the solid sides) is metal and it uncilps so you can dust inside the radiator between the two sections. Some people prefer that.
Some rads also allow you to feed the pipework from behind. Some people prefer that.
Thanks. I wasn't sure what overshoot was but I think you explained it. Is it basically when the room heats up too much. The thermostat might switch off at say 20C but because there is so much hot water sitting in the rad, the rad continues to emit and the room becomes say 23C? I can't believe you have managed to fine tune it to within half a degree!
BTW, on a different topic: I now realise that the water setting in the Barlo programme is irrelevant because the heat loss from the room is the same regardless of the water temperature. The water temperature only comes into play when deciding which rad will match that heat loss and I am not using the programme to choose the radiators.
Do the sides remove for dusting or just the grill? The cheap ones I have bought from Toolstation allow the grill to be removed but you cannot remove the sides without taking off the pipes.
Yes (although I doubt it would normally be that much). I believe some of the more advanced heating controllers compensate, i.e. once they've learned what the overshoot is, they switch off earlier and use the overshoot to get the the required temperature. If the heating controller is fully integrated with the boiler, it can reduce the radiator temperature as the difference between current room temp and thermostat setting is closing, to avoid overshoot, and can also take into account outside temperature (hence heat loss through walls). Using the outside temp is called weather compensation.
However, since I design/build my own heating controllers, I haven't actually played with commercially available ones.
I used to have gas wall heaters, before the central heating. The dining room had a Drugasar gas wall heater with proportional control, and that kept the room to within 0.1C, once I'd pulled the thermostat phile out from the insides of the heater and hung it in the air inlet underneath.
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