- Messages
- 34,368
- Solutions
- 2
I would say the pump is sized correctly you have a few too many rads for a 15-60 balance the rads first and come back
Discuss Real world testing example of Condensing Boiler in older home in the Central Heating Forum area at PlumbersForums.net
Interesting thread. This is the kind of investigative spirit we need to have if we're really to make meaningful improvements to heating systems.
Re the infra-red thermometer, I find they work really well. However, they are usually geared to high-emissivity surfaces (it should normally explain that in the destructions). As such, any reasonably shiny metallic surface can't really be read accurately as it is a low-emissivity surface. However, there is an easy fix in that a piece of masking tape on the pipe can be used as a reliable test point.
I'm not sure re Firebird condensate trap but some traps, to avoid the waste pipe freezing up, fill up the trap with condensate and then blows this down and refills again so on the off chance that this is occuring keep a eye on it but I wouldn't hold my breath as firebird supplied a plastic trap originally which used to melt.
I am going to carry out a test on just one rad soon because as you say, the only sort of fit is if the flow temperature falls as well, see below. I'm quite happy that I had a flow rate of 5LPM both by throttling the 5M pump setting to replicate yours and then at a pump head of ~ 3m unthrottled to give me the same 5LPM. As the boiler output was fairly constant (cycling) at 45 to 50% then the only scenarios that sort of fit are the last two below, ie a flow temp of 64C & return of 35C for 50% output and 45% output at 60C/34C, I didn't see my return going below 42/43C, the only explanation I can give for a apparent low flow temp is that a oil fired boiler acts as a 20/25 litre buffer tank and with the burner off perhaps cold return water flows from the flow side until the burner "catches up" and reheats the buffer??.
View attachment 72892
Carried out the TRV test on one X 1.7kw rad and as expected, the TRV was just copening/closing but keeping fairly tight control of the mean rad temp at ~ 42/44C which gave the required rad output of 0.6kw to maintain a room temperature of 20/22C. The boiler had very long cycling times of around 2.5 mins on and 35 minutes or more off. I then progressively introduced the remaining rads (all TRVd) and their mean rad temps reflected the outputs required, the combined return temp didn't vary hugely ~ 39/45C.
Its very difficult to get a good reading in the heat pac due to restricted space but initially it actually seems to rise a little but I suspect this is because the boiler flow pipe turns down immediately where as the boiler return goes out the side of the boiler and then very gradually rises so I think the boiler contents are inclined to "circulate" back through the return. The cycling time matches ~ the rad heat demand but its not that simple as the boiler once it cuts back in when the stat reaches ~ 60/65C has to reheat say 20/25 litres of boiler water from ~ 40c to its cut out of 70C so requires ~ 0.9kwh which takes ~ 2.7 minutes from a 20kw boiler. In general, once other rads are brought back on line then the % firing time does reflect the heat demand.
What are the dimensions of the kitchen rad and is it a double or single?.
Try with the pump speed on two instead of one
Tbh doesn’t really matter temp as that’s not a limiting factor
And tbh if your trying to balance it needs to be on the return as your throttling flow else
Would be best practice
All my TRVs are on the returns and I can certainly balance/reduce rad outputs by throttling the lockshields, but as I said I reckon I would find it extremely difficult to get all rads to a dT of say 10C or 15c or whatever, having TRVs on all rads, once they throttle in will give a variable dT depending on the room temperature(s). I have watched my boiler return over the past few days and it never goes below 42/43C and probably averages more like 45/46C. I really think the best way to get a relatively constant low (but not below 38/ 40C for oil firing) is to use flow temperature control. You could get limited return temperature control by controlling the flow with a smart circ pump but this only allows a minimum rad output of ~ 58% whereas flow temperature control (if achievable) allows rad outputs as low as 30% with return temps not falling below ~36/38C.
View attachment 73023
Rad stats give individual room control so why throttle the main if the room stats are set properly and operating properly?. The boiler return temp will then be at its lowest possible but individual rad returns will vary from say 50/55C downwards, consistent with your requirement for a 70C constant flow temp, my rad stats give excellent individual room control.
Just read in a UPS 2 8M pump replacement post that a Dab Evoplus & a Grundfoss Magna 3 are suggested, you might be interested from the point of view that the also do temperature control, might be worth a look?.
Prob is the magna3 eg dt controlled with all the kit ends up around £600
Thinking more about it, would be inclined to agree with you, anyway when you balance your system you can just throttle the valve again until you get a average return temp of say 40Cish? and see how the system performs. if it is OK, then far cheaper maybe just to install a thermostatic valve in the line?. if it doesn't work you can just open it fully.
If you can put up some instructions / wiring diagram will have a look later on
Reply to Real world testing example of Condensing Boiler in older home in the Central Heating Forum area at PlumbersForums.net
We get it, advertisements are annoying!
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.