TonyMorris Posted March 13, 2023 Share Posted March 13, 2023 Hi, I'm hoping to get some advice. We have an Airflow DV145 MVHR. I have a problem with the exhaust air being warmer than the inside air but no idea why. Airflow technical support weren't very helpful either. It's bizarre. What tends to happen is when the front cover of the unit is opened/the system is off for 10 minutes then the readings are reset and the exhaust air is cool for a while. But 'sometime' later (even sometimes only after a day or two later) the exhaust air is showing as warm again. I thought it may be a problem with the extract air motor warming the air, but the unit power is only 20W so I think that's not the issue. I had the bearings replaced in case it was somehow friction, but no luck there either. I'm wondering whether the heat recovery is working in reverse or there's a blockage or something weird in the airflow? But then why is usually fine 'for a while'? Any ideas!? Thank you!! Link to comment Share on other sites More sharing options...
Mr Punter Posted March 13, 2023 Share Posted March 13, 2023 Is it plumbed in correctly? Link to comment Share on other sites More sharing options...
SteamyTea Posted March 13, 2023 Share Posted March 13, 2023 And the temperature probes wired in right. Also summer bypass not changed to winter. There is also the terminology, which is not that intuitive. I think Exhaust is the air leaving the room, not the room air being expelled out the MVHR unit, though I am never quite sure. Link to comment Share on other sites More sharing options...
Temp Posted March 13, 2023 Share Posted March 13, 2023 If I'm looking at the right thing... they have left and right hand models. Would be easy to plumb them in wrong but not sure what effect it would have.. Link to comment Share on other sites More sharing options...
Mr Punter Posted March 13, 2023 Share Posted March 13, 2023 21 minutes ago, SteamyTea said: I think Exhaust is the air leaving the room, not the room air being expelled out the MVHR unit, though I am never quite sure. No I think exhaust air is air leaving the building from the unit, but I agree it is not always intuitive. The stale air from the room to the unit is extract air. Link to comment Share on other sites More sharing options...
SteamyTea Posted March 13, 2023 Share Posted March 13, 2023 Just now, Mr Punter said: No I think exhaust air is air leaving the building from the unit, but I agree it is not always intuitive. The stale air from the room to the unit is extract air. Yes. I think you are right. Link to comment Share on other sites More sharing options...
TonyMorris Posted March 13, 2023 Author Share Posted March 13, 2023 I think it's plumbed in correctly (or mostly correctly), also as this is not always a problem.! Will take a video of the settings and the unit and see if that prompts anything! Please standby... Link to comment Share on other sites More sharing options...
TonyMorris Posted March 13, 2023 Author Share Posted March 13, 2023 Here's a video of the settings: https://streamable.com/a6nrck Thanks! Link to comment Share on other sites More sharing options...
joth Posted March 13, 2023 Share Posted March 13, 2023 Can you get another thermometer into the exhaust airstream, to confirm if it's outgoing air is actually at that temperature, or if it's an error with the probe / controller? From the second photo, with 5°C outside but your supply air at 16°C it would appear the heat exchanger is working (or, you're violating the Law of conversation of energy) which leads me to suspect something is misreporting numbers. Link to comment Share on other sites More sharing options...
Mr Punter Posted March 13, 2023 Share Posted March 13, 2023 If this is in the winter I would expect to see INDOOR as the highest temperature as this is the stale air being taken into the unit and OUTDOOR being the lowest as it is outside air. After passing through the heat exchanger the INDOOR surrenders heat and is expelled at a lower temperature, recorded as EXHAUST. Meanwhile OUTDOOR takes on some heat and is fed to the rooms, recorded as SUPPLY. Link to comment Share on other sites More sharing options...
Mr Punter Posted March 13, 2023 Share Posted March 13, 2023 I think the EXHAUST sensor is actually recording the INDOOR. Link to comment Share on other sites More sharing options...
TonyMorris Posted March 13, 2023 Author Share Posted March 13, 2023 I'll try pulling the exhaust sensor out of the duct to check it - will keep you posted! Thank you. I'd laugh if that is the root cause - the guys who installed this also managed to make a real mess of the heating controls (different system) so I wouldn't put it past them... Link to comment Share on other sites More sharing options...
TonyMorris Posted March 13, 2023 Author Share Posted March 13, 2023 Ok, so the sensor is correct. I put my hand around it and the temp went up and down. It might not be calibrated fully, but it's about right. The big riddle though is... when I put my hand into the fan air (see the photo where the fan is not connected/sat properly) it seems to be warm. So where is that heat coming from!? I've literally no idea. The vent at the side of the unit seems clear. I'm very confused! Link to comment Share on other sites More sharing options...
TonyMorris Posted March 13, 2023 Author Share Posted March 13, 2023 I feel like the heat exchanger is working back to front or something like that... but perhaps that's not possible! Link to comment Share on other sites More sharing options...
Petrochemicals Posted March 13, 2023 Share Posted March 13, 2023 There seems to be a much energy going missing anyway, even if the exhaust is hot, I'd start there Link to comment Share on other sites More sharing options...
TonyMorris Posted March 13, 2023 Author Share Posted March 13, 2023 It's back to cold again this eve... a riddle Link to comment Share on other sites More sharing options...
joth Posted March 13, 2023 Share Posted March 13, 2023 1 hour ago, TonyMorris said: It's back to cold again this eve... a riddle That still doesn't look right: it's supplying air warmer than the internal temperature. Where is the extra energy coming from? Link to comment Share on other sites More sharing options...
Conor Posted March 14, 2023 Share Posted March 14, 2023 My money is on the preheater being on at the same time as some sort of bypass (outdoor air being preheated, but then bypassing the exhnager and going back outside, somehow, possibly a partially open bypass damper). I know my unit can have different scenarios depending on conditions, from full summer bypass, partial, full internal bypass or a mix of the two. Once outdoor temp rises enough to not need the preheater, then things return to normal. Either way, some sort of sensor issue. Link to comment Share on other sites More sharing options...
TonyMorris Posted March 14, 2023 Author Share Posted March 14, 2023 11 hours ago, joth said: That still doesn't look right: it's supplying air warmer than the internal temperature. Where is the extra energy coming from? I suspect the inside air sensor is in the plant room (will try to find it) so may not represent the true temperature in the rooms (17/18 is more likely) Link to comment Share on other sites More sharing options...
TonyMorris Posted March 14, 2023 Author Share Posted March 14, 2023 3 hours ago, Conor said: My money is on the preheater being on at the same time as some sort of bypass (outdoor air being preheated, but then bypassing the exhnager and going back outside, somehow, possibly a partially open bypass damper). I know my unit can have different scenarios depending on conditions, from full summer bypass, partial, full internal bypass or a mix of the two. Once outdoor temp rises enough to not need the preheater, then things return to normal. Either way, some sort of sensor issue. Thanks - I’ll see if I can find anything on the preheater settings (or maybe I’ll disconnect it!) Link to comment Share on other sites More sharing options...
TonyMorris Posted March 30, 2023 Author Share Posted March 30, 2023 On 14/03/2023 at 11:21, TonyMorris said: Thanks - I’ll see if I can find anything on the preheater settings (or maybe I’ll disconnect it!) Ok, latest update - definitely not a pre heater issue as it’s disconnected, but I did discover the outside wall vent was very dirty at the air intake. So I’m hoping that a lack of air coming into the unit was somehow meaning the exhaust air was receiving the heat that was meant for the fresh air. that may be impossible but it’s my theory! Will post more here if I discover something else 😊 Link to comment Share on other sites More sharing options...
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