John Carroll

Doctor Willis will be delighted if his heaters are working as designed, ie convection only!. 12mm ID piping allowing ~ 60M/loop will have a friction loss of around 0.19M @ 1.0LPM, 0.4M @ 1.5LPM, and 0.68M @ 2.0LPM. Maybe increase the pump head temporarily to say 2.5M or even 3.0m (as long as you don't run out of power), note the flowrate, the % error will then be less, and the flowrate at 0.7M will be the sqroot of (0.7/2.5) or sqroot of (0.7/3.0) X the indicated flowrate.

Got the new EPH TRV, its indexed 0 to 5. At a OAT of 7C and leaving the TRV outside for a hour or so, I only have to decrease the setting to 4.0 when the actuator then contacts the push pin. Inside, after allowing it to heat soak for another hour or so, the push pin starts to move immediately on turning the actuator from index 5 (max). At setting 2.5 (which gives me ~ 18C), the valve is only ~ 1.5MM off its (closed) seat at a temperature of 15C or so.

A excellent choice and a lovely pump, IMO!!, I have a 5 year old 6M version (no flow display) in a oil fired conventional rad sytstem, these pumps, as you are no doubt aware, can have the head incrementally changed in 0.1M steps in both CP and PP modes, to a min 0.5M minimum (on mine anyhow) and yes, just tried mine, it does display 2W at 0.5M in CP (and) PP mode. Even so, you must be circulating something through your system, would expect at least 0.5Ms/hr, say 8.0LPM, ~ 5W or more. What is the pump flowrate showing??.

What make/model of pump do you have MIke and what mode/setting is it on, where are you reading the 2W?, I really can't see it pumping anything at that minuscule power, any A rated pump I've come across will require at least a closed valve 4W at the lowest setting, if you can get a accurate reading then the pump curves will give very accurate indication of the circulation rate, most A rated pumps now not only display the pump power in Watts but also the flowrate in M3/hr, very useful.

kw is a unit of power, a gas boiler might have a output of say 25 kw (my upper/lower case sense of "kw" might be incorrect but doesn't matter from a thermodynamic point of view) so you have a 25 kw Boiler, etc.

My maths?. I've allways used kw = (flowrate (LPM) x 60 x temperature rise, dT (deg.C)/860 so, kw = LPM*60*dT/860 or any variation of this once you know two of the values I used a total flowrate of 12.5LPM and 2 X 3kw heaters. From the above, kw = LPM*60*dT/860 dT = kw*860/60/LPM One 3kw heater, with a flowrate of 6.25LPM (12.5/2), will give a temperature rise, dT, of, 3.0*860/60/6.25, 6.88C, if the heater inlet temp is 25C, then the outlet temp is, 25+6.88, 31.88C, two heaters (on) in parallel will give a flowrate of, 2*6.25, 12.5LPM at the same dT of 6.88C with the same outlet temp of 31.88C. Two heaters in parallel with one switched OFF will give a 0.0C, dT , the other (ON) will give a dT of the above 6.88C. You now have 6.25LPM at 25C mixing with 6.25LPM at 31.88C. Let Tm = mixed temperature So, 12.5*Tm = (6.25*25)+(6.25*31.88) So 12.5*Tm = 156.25+199.25, 355.5 Tm = 355.5/12.5, 28.44C If one heater is OFF and the water flow through it shut off then 12.5LPM is flowing through the switched ON heater with a dT (kw*860/60/12.5) of 3*860/60/12.5, 3.44C, to give a outlet temp of, 25C+3.44C, 28.44C, the same as the above with the flow split between the two heaters. Two heaters in series, both ON, flowrate 12.5LPM. dT in both/either heaters will be, (kw*860/60/LPM), 3*860/60/12.5, 3.44C, outlet temp from bottom heater, 25C+3/44C, 28.44C, outlet temp from top heater, 28.44C+3.44C, 31.88C (same as with both parallel heaters ON, above) Two in series, one off, one ON, dT through ON heater, (kw*860/60/LPM), 3*860/60/12.5, 3.44C, outlet temp, 25C+3.44C, 28.44C, dT through top (OFF) heater 0C, outlet temp, 28.44C. (same as with one heater only on in parallel). You have ~ 800M of UFH piping, a loop might consist of up to 100M of piping with a flowrate of 2.0LPM giving say 6C to 8C dT at a flow temp of ~ 40c/45C, so each loop (assuming a dT of 7C) will emit, (LPM*60*dT/860), 2.0*60*7/860), 0.977kw, say 1.0kw, you should have ~ 8 loops so, at least 8kw if running at the above conditions, 45C/38C, so obviously 3kw will give a very much reduced output (it will give exactly 3kw if the heater stat never cuts out) because of the very low loop flow/return temps, each loop might/should have a flow meter tube showing the flowrate in LPM, if so, just add them to get the total flowrate.

Yes, it would and will, but the outlet flow and temperature will be the same, whatever configuration you use or way you install the heaters.

Will do so now!.

I used ~ 2.0LPM/Loop, dT ~ 6C, 6 loops, ~ 5kw, but doesn't matter as these 3 examples give the same output and temperature, mixing or no mixing, I just used 25C as the inlet temperature.

With the 2 in parallel, say 3kw each, assuming a total flowrate of 12.5LPM, 6.25LPM through each, gives a dT of 6.88C, a return temp of 42C gives a flow temp of 48.88C. 2 in series, flow through both is 12.5LPM, dT through each is 3.44C, it enters first heater at 42C, leaves at 45.44C, enters the second at 45.44C, leaves at 48.88C. Switch one off (still in series) dT through first (12.5LPM) is 3.44C and 0C through the second, flow temperature 45.44C. 2 in parallel, one switched off, dT through switched on one, (at 6.25LPM), 6.88C, flow temp 48.88C, dT through second (switched OFF) 0C, flow temp 42C, 6.25LPM at 48.8C mixed with 6.25LPM at 42C gives 12.5LPM at 45.44C.

Non linear, yes, often wonder should there be different WC curves for rads and UFH, if you require a room/heat demand of say 1.0kw at 20C and to compare a rad with the same conditions with a typical UFH installation, assume a 2.45kw rad is installed, if heating demand is 1.0kw then the rad conditions to achieve this will be, flowtemp/returntemp/dT/flowrate, 48C/42C/6.0C/2.38LPM, (a T25 rad), now just assume OT conditions remain the same and you need to increase the room temperature from 20C to 22C, the rad conditions now have to become 52.3C/45.7C/6.6C/2.38LPM, (a T27 rad), if the room was heated with UFH with the pipeloop(s) sized to give 1kw at ~ the same conditions, (48C/42C/2.38LPM), what UFH flowtemperature would be required to give a 22C room temperature?, doubt if it will be the same as the rad requirement of 52.3C. This should be analogous to changing OT conditions with WC?.

If you just leave the UFH run 24/7, what do you think your UFH system would stabilize at, heat output wise? and/or using the OPs actual data of a few posts back of UFH flowrate of 10LPM with flow/return of 48C/41C, output 4.88kw, would you expect this to stabilize at, assuming no or little change in OAT?. I thought running UFH 24/7 is the preffered way even though it obviously won't give steady room temperatures.

Take as many readings as you can from all sources when the heating has been on for say a hour, also the ufh manifold flowrates. A cycle is the burner ON time + the boiler OFF time, can you note both of these.

Can you post the readings again from the UFH manifold after say 5 minutes of burner firing. also boiler flow/return temps and any other temperature readings to hand. If its 5min ON/3min OFF cycle then the UFH demand is ~ 6*5/8, 3.75kw, minimum. Also try and note the boiler flow temp when it fires up and the exact time it takes to reach its maximum temp before modulating/reducing to 60C or so, it will then rise to 65C and burner trip/cycle.

Close it down a touch, clockwise.

Via the by pass rad, I think you said a rad valve was 3/4 of a turn open?, try a 1/4 to a 1/2 turn open.

You really can't do anything about the cycling due to the boiler's minimum output being higher than the heat demand but so what?, your boiler isn't short cycling which I I would term a boiler which can't get away without multiple firings and fires for only a minute or so like yours was previously, its grand talking about low and slow when/if you have a boiler that can modulate down to a couple of kw, cycling will cost a few quid more in fuel costs but I wouldn't be rushing off to buy a Viessmann or such like to achieve this especially if your present boiler is reliable, some worry about the extra wear and tear but this doesn't worry the users of smart CH systems like Evohome which can cycle the boiler up to 6 times/hr (more often than yours) even when the heat demand exceeds the boiler's minimum output. I have a nearly 20 year old oil boiler that must have cycled thousands of times (because it cant modulate) and it hasn't cost a single cent in repairs, I dare say there are plenty of gas boilers likewise that continually cycle and run for years without any repairs. Anyhow I've attached a modified spreadsheet that I put together for someone with a Vaillant Ecotec 630 boiler with a low loss header that will only run properly in one mode of operation, it may be of interest, if nothing else. You will notice in the sheet "UFH Only with Bypass" that you have a bypass flow of around 3.3LPM which you may be able to reduce a little without compromising the boiler firing and reduce the return temp from its present ~ 50C to say 45C or so which would lead to a nice bit of extra condensing and greater boiler efficiency. UFH + Rads Extract Rev0.xlsx

Yes, theoretically, the boiler should be able to refire once the flow temp falls to its target setting, the burner cut out has to be higher than the target temp otherwise the burner would cut out every time the target temp is reached, it is usually set at 5C to allow a little overshoot without tripping the burner on fire up and sudden target temp changes, a decrease in target temp > 5C below the flow temp will usually trip the burner as well. Is your target temp 30C? and what is the anticycle time set to? is it like the Vaillan't look up table or exactly as you input it, ie a 3 min anticycle time is exactly 3 minutes?.

Slight change to Spreadsheet as one value couldn't be changed without unprotecting the sheet. UFH Calculations with Bypass Extract Rev1.xlsx

So, the return temp to the boiler must be 41C, the (boiler) flow temp is 60C, dT, 60-41, 19C, UFH dT, 48-41, 7C, boiler flowrate, 10*7/19, 3.68LPM, so there obviously is HW being recirculated to give that higher return temp, the only downside of this is that the boiler efficiency will be lower at the higher return temp so maybe just look at this, rather than trying to get longer cycle times etc by creating a bigger heat demand or whatever, your system is, IMO, performing very well, why not leave it be. The "picture" below might be easier to understand UFH mixing etc and you can do your own calcs. UFH Calculations with Bypass Extract Rev0.xlsx

Cant see the bottom (return) gauge properly but if its the same as the top one (scale wise) then maybe reading 40/42C ish? so ~ 7C dT, fairly normal, so UFH output 2.5*4*60*(48-41)/860, 4.88kw?, or there abouts.

The cut in temp on the majority of (gas fired) boilers is when the anticycle time has elapsed once the flow temp is target temp - 5C, I have seen posts re some boilers which have a settable (negative) hysteresis where the cut in is either at this target-hysteresis OR the anticycle time.

The (any) boiler should not refire until the flow temp is target temp - 5C, 60-5, 55C in this case, any modulating boiler cannot work if either the cut in/cut out are at target temp.

Can you go to the UFH manifold and read off the flowrates from each loop as accurately as possible from the flow meters ("glass tubes") and also the manifold flow & return temperatures when the boiler has been firing for say 5/7 minutes, also note the boiler flow & return temperatures. Your boiler may have a internal bypass which would account for the difference in displayed return temp & the measured return temp, you could alos shut that bypass after say 5 minutes, note the boiler flow&return temps before shutting it and after another say 1 minute recheck those temperatures, I would then recommend returning the by pass to its original setting. You are doing very well with that cycle time IMO, your cycle time suggests a UFH/boiler demand of at least, 6*9/12, 4.5kw but will probably be more as the boiler will fire at 20kw (its max on CH) for a few minutes to get the flow temp up to its target temp of 60C and then ramp down to its minimum of 6kw, your manifold data will give a fair idea of what the demand actually is (roughly). Edit: whats this €2.50 cost? is it per day or what.

Maybe not quite what you are looking for. https://blog.heatspring.com/2-pipe-versus-4-pipe-buffer-tank-configurations/