HughF Posted October 28, 2023 Share Posted October 28, 2023 I recently installed a new central heating system, bunch of new rads, and three fan coils. How can I balance my rads if the trv is on the outlet of the rad and the lock shield is on the flow? They are tboe with the trv at the top. I have trvs upstairs only (ashp, open loop, no buffer)… Link to comment Share on other sites More sharing options...
marshian Posted October 28, 2023 Share Posted October 28, 2023 2 hours ago, HughF said: I recently installed a new central heating system, bunch of new rads, and three fan coils. How can I balance my rads if the trv is on the outlet of the rad and the lock shield is on the flow? They are tboe with the trv at the top. I have trvs upstairs only (ashp, open loop, no buffer)… Same way as if the TRV is on the inlet and the lockshield is on the outlet - where the LS and the TRV are makes no difference to balancing IMO if you throttle the flow on the inlet or throttle the flow on the outlet you are still throttling the flow...... Link to comment Share on other sites More sharing options...
HughF Posted October 28, 2023 Author Share Posted October 28, 2023 I need to throttle the flow to get the delta-t across the rad up, so I need the lockshield on the outlet, don’t I? This is on a heat pump system, open loop, no buffer. My rads are running at a delta-t of about 1.5 and a thermal camera shows the flow is short-cutting between flow and return across the rad. Link to comment Share on other sites More sharing options...
HughF Posted October 28, 2023 Author Share Posted October 28, 2023 All the rads in the system are heating up, even ones further away, it’s just the flow through the rad is high. Downstairs rads have standard valves so I can throttle the flow on the outlet, but my engineering head says the upstairs ones need to be the right way round. Link to comment Share on other sites More sharing options...
markocosic Posted October 28, 2023 Share Posted October 28, 2023 If dT is too low *everywhere* dial back the pump before you throttle valves. If a radiator that's been piped backwards and has the return at the top then hot, buoyant, water, is always going to piss off down the return in preference to staying in the rad. Plumber needs to change that for the rads not to act as bypasses with the flow looking like an "r" shape. Link to comment Share on other sites More sharing options...
HughF Posted October 29, 2023 Author Share Posted October 29, 2023 7 hours ago, markocosic said: If dT is too low *everywhere* dial back the pump before you throttle valves. If a radiator that's been piped backwards and has the return at the top then hot, buoyant, water, is always going to piss off down the return in preference to staying in the rad. Plumber needs to change that for the rads not to act as bypasses with the flow looking like an "r" shape. Ill identify the flow/return on each radiator and make a plan for re-piping. I imagine it will be easier to just swap from TBOE to BBOE, that way the flow doesn’t matter? Link to comment Share on other sites More sharing options...
sharpener Posted October 29, 2023 Share Posted October 29, 2023 14 hours ago, HughF said: I recently installed a new central heating system, bunch of new rads, and three fan coils. How can I balance my rads if the trv is on the outlet of the rad and the lock shield is on the flow? They are tboe with the trv at the top. I have trvs upstairs only (ashp, open loop, no buffer)… Check that the TRVs are a reversible type, not all are. The sensor measures the air temperature and there is an argument that measuring it at 2 -3 ft above floor level is actually better. If the rads are all of the same pattern set the lockshield valves so it takes the same time for the hot water to reach the return pipe on each rad from a cold start. This works bc the volume of water is approx proportional to the output of the rad and so it makes the flow proportional to the output as well. Doing this you might get away with the wrong connections tho if the plumber will correct it for free you might as well get him back. Link to comment Share on other sites More sharing options...
JamesPa Posted October 29, 2023 Share Posted October 29, 2023 4 minutes ago, sharpener said: If the rads are all of the same pattern set the lockshield valves so it takes the same time for the hot water to reach the return pipe on each rad from a cold start. This works bc the volume of water is approx proportional to the output of the rad and so it makes the flow proportional to the output as well. Doing this you might get away with the wrong connections tho if the plumber will correct it for free you might as well get him back. Hadn't heard that method before, can you explain the method in a bit more detail as I'm being a bit thick and not following? Link to comment Share on other sites More sharing options...
HughF Posted October 29, 2023 Author Share Posted October 29, 2023 The plumber is also my builder mate, who’s doing our extension/kitchen. I don’t really want to lump him with another job at the moment, nothing I can’t take care of (I do plumbing anyway)…. I’ve identified that the rad in the above photo is plumbed correctly (inlet at the top), and I’ve managed to get delta-t 2 ish…. Need to pop the front off the fan coils and set the ball-o-fix valves down on those first I think. Link to comment Share on other sites More sharing options...
markocosic Posted October 29, 2023 Share Posted October 29, 2023 19 minutes ago, HughF said: I’ve identified that the rad in the above photo is plumbed correctly (inlet at the top), and I’ve managed to get delta-t 2 ish…. Need to pop the front off the fan coils and set the ball-o-fix valves down on those first I think. It looks - from the thermal camera - like the flowrate is too high for stratification to happening. A dT of 2 on the heat pump side isn't a catastrophe (will cause increase pumping cost but meh); it's the fact that most of the water "isn't in use" because only a small part is running around in bypass that's causing your cycling. Link to comment Share on other sites More sharing options...
dpmiller Posted October 29, 2023 Share Posted October 29, 2023 yep, I'd be reducing the pump speed a bit. Easy on the iVT-9 Link to comment Share on other sites More sharing options...
HughF Posted October 29, 2023 Author Share Posted October 29, 2023 (edited) 22 minutes ago, dpmiller said: yep, I'd be reducing the pump speed a bit. Easy on the iVT-9 Max speed of 60% and try that? edit: pump min of 20, max of 75…. Seems to be throttling back a bit more. Still need to get balancing and figuring out the flow direction. Edited October 29, 2023 by HughF 1 Link to comment Share on other sites More sharing options...
HughF Posted October 29, 2023 Author Share Posted October 29, 2023 Adjusting the lock shield valves on the upstairs rads seems to make zero difference to the delta-t across the rad, so that would suggest that the pump speed is ideal, would it not? I can get a delta-t of 4 when the flow temp ramps up, and the delta-t drops back as the compressor shuts down. Link to comment Share on other sites More sharing options...
dpmiller Posted October 29, 2023 Share Posted October 29, 2023 adjusting the lockshields *must* alter the DT. After all, if they're closed enough there is *no* flow... Link to comment Share on other sites More sharing options...
HughF Posted October 29, 2023 Author Share Posted October 29, 2023 (edited) Yep, I get that, but I’d expect them to be a bit more granular, it’s all the same for 95% of the range, then it’s off…. I upped the bottom end of the pump pwm from 20 to 30, it seems to overshoot it’s temperature setpoint by 5 degrees or so at such a low pump pwm. Give me air2air all day 🤣 Edited October 29, 2023 by HughF Link to comment Share on other sites More sharing options...
SimonD Posted October 29, 2023 Share Posted October 29, 2023 8 minutes ago, HughF said: Yep, I get that, but I’d expect them to be a bit more granular, it’s all the same for 95% of the range, then it’s off…. What brand of lockshield valves do you have? Some of them are total sh!te when it comes to adjustability. However, given the nature of hydronic systems, sometimes you find curious behaviour with valves at certain settings too. Link to comment Share on other sites More sharing options...
JohnMo Posted October 29, 2023 Share Posted October 29, 2023 21 minutes ago, HughF said: Give me air2air all day 🤣 It's call commissioning, that's why so many installs are pants, it just not done, there is plenty of fine tuning to do. Then you need to run it different modes to find out which is most effective from a heating perspective and running costs. 1 Link to comment Share on other sites More sharing options...
billt Posted October 29, 2023 Share Posted October 29, 2023 58 minutes ago, HughF said: Yep, I get that, but I’d expect them to be a bit more granular, it’s all the same for 95% of the range, then it’s off….🤣 Have a read of https://www.heatgeek.com/what-you-dont-know-about-lockshield-valves/ which includes this graph. I've just gone through this with my new system. I used IMI valves which are supposed to be reasonably good, but I still found that they had to be practically closed before the adjustment started. Link to comment Share on other sites More sharing options...
HughF Posted October 29, 2023 Author Share Posted October 29, 2023 (edited) Ok, something interesting has happened… I’ve put 1.5 degrees on all the weather comp points and it’s sitting here ‘almost’ ticking along at minimum output. That’s encouraging. I’ve got the extra fan coil in the bathroom running now, that’s what’s changed since yesterday. Short cycling seems to have reduced. Edited October 29, 2023 by HughF Link to comment Share on other sites More sharing options...
HughF Posted October 29, 2023 Author Share Posted October 29, 2023 5 hours ago, SimonD said: What brand of lockshield valves do you have? Some of them are total sh!te when it comes to adjustability. However, given the nature of hydronic systems, sometimes you find curious behaviour with valves at certain settings too. Cheap ones from Screwfix, unfortunately…. Link to comment Share on other sites More sharing options...
DamonHD Posted October 29, 2023 Share Posted October 29, 2023 6 hours ago, HughF said: Yep, I get that, but I’d expect them to be a bit more granular, it’s all the same for 95% of the range, then it’s off…. I upped the bottom end of the pump pwm from 20 to 30, it seems to overshoot it’s temperature setpoint by 5 degrees or so at such a low pump pwm. Give me air2air all day 🤣 My experience with TRV bases at the other end was that typically << 10% of the range was anything other than full flow or no flow. Link to comment Share on other sites More sharing options...
marshian Posted October 29, 2023 Share Posted October 29, 2023 7 hours ago, billt said: Have a read of https://www.heatgeek.com/what-you-dont-know-about-lockshield-valves/ which includes this graph. I've just gone through this with my new system. I used IMI valves which are supposed to be reasonably good, but I still found that they had to be practically closed before the adjustment started. Over sensitive lock shield valves is why I went for drayton EB bodies for the TRV's - 6 available presets does all the coarse adjustment and if you need to fine tune you can use the lock shield (only had to do that on towel rails) Link to comment Share on other sites More sharing options...
sharpener Posted October 29, 2023 Share Posted October 29, 2023 (edited) 14 hours ago, JamesPa said: Hadn't heard that method before, can you explain the method in a bit more detail as I'm being a bit thick and not following? For a given mfr and construction (plain or convector) the water volume in rad is pretty much proportional to surface area (w x h x # of panels). Output is pretty much proportional to surface area too. For identical delta T you want flow rate to be proportional to heat output. Eliminate surface area from both sides and you get desired flow rate proportional to volume. This means equal time to displace the cold water with hot in each rad regardless of size/output. QED. Neat or what? For convector fins the output is roughly 50% more so the return pipe should start to flow hot in 2/3 the time of the plain ones. Edited October 29, 2023 by sharpener 1 Link to comment Share on other sites More sharing options...
HughF Posted October 31, 2023 Author Share Posted October 31, 2023 (edited) With the pump minimum set to 30%, I arrived on-site tonight to find all the rads evenly warm. Heat pump had been ‘on’ since 0600, the room stat is disconnected at the moment. I had throttled the fan coils down to get me as close to dT5 as I could, and left the rads all open, when I last played around with this on Sunday evening. Edited October 31, 2023 by HughF Link to comment Share on other sites More sharing options...
HughF Posted November 25, 2023 Author Share Posted November 25, 2023 Update: haven’t touched the lockshields forks month, but I managed to get the ufh plumbed and wired up. Still one fan coil down so we’re just ticking along with emitter rejection slightly under the minimum modulation value of the heat pump, so we’re still cycling. Hoping to get the electrician back on site this coming week to get the kitchen second fixed and the last fan coil installed. That should give us 1100-1400w more emitter capacity and bump us above the 3.3kW minimum. Hoping to see the heat pump settle down to its 800w minimum then and just tick along in the background. Link to comment Share on other sites More sharing options...
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