Hi Gents,
Thanks for taking a look. Have a real puzzle on our hands. First HVAC tech was out three times, out of ideas. Having a second company come in tomorrow, wanted to provide him with good info to help him troubleshoot if at all possible.
Have a 2-pipe fan coil forced air system in the main hallway, and a horizontally mounted ERV in the ceiling of the bathroom in a residential high rise, large city less than a mile from a large lake, with warm summers (70-95F) and cold winters (15F-40F).
We had consistent excess heat issues in the “winter” (Oct-May) pre-switchover from heat to cooling (like 75-85F with exterior temps of 40-55F). I think I literally never had to turn on “heat” to keep it warm. Only to test it. Seems to work fine. Even when it was 25F outside, no heat required. Unit 75F or so. The instant we had cooling available, unit works great. Able to get the unit interior down to 68-70F or so at the coldest, with exterior temps 75-95F or so. Controllable within 2-3F almost all the time I wanted to adjust it. Very consistent. Been noticeably humid inside in the summers, and very dry in the winters (~15-25% ?). Had about 60-75% on average humidity for most of the summer
The condo is about 3 years old, relies on mechanical ventilation. Unit seems very well-sealed otherwise. Large glass windows on east side, provides direct sunshine for 1-2 hours at most. Warms noticeably during that time, but no south or west exposure at all, so good for the rest of the day. In summer, fan coil unit has a tough time keeping up for that direct sun period and it might warm slightly above set point by a degree or two, but under control normally within an hour or so in the summer. In the winter, had little relief at all during the day after this initial “warming”. Even did a test by opening the patio door at midnight (only fresh air I can get aside from ERV) with temps close to freezing (shouldn't with a fan coil, I know) and interior temps still bounced back up to 75F+ within an hour.
Tech details:
- Unit is a Reverseomatic “Superior” series ERV (RERV-S100)
- Two pipe fan coil system, May-Sept summer cooling mode, Sept-May winter heating mode.
- Multi-speed fans, 3 stage if I recall correctly.
- There seems to be an exhaust vent located in the bathroom, airflow “suction” noticeable when ERV on both low and high speed settings. One other exhaust fan above the range in the kitchen, but that seems to have its own independent fan (no airflow when off), and possibly it’s own ducting.
- Unit is on the top floor of the tower with just a mechanical room above (various building chillers/boilers/elevator mechanical rooms, presumably)
- Unsure if it’s a “fully ducted” ERV or if the ducting is tied into the fan coil unit as well.
Troubleshooting so far:
- Tested the valve controlling the flow of hot water (actuator?) on the fan coils (during “winter”), tech commented it was a somewhat cheap valve and possible it could fail, but working fine on his inspection. Been using it all summer for A/C, and seems to work great for that. Good interior temp control. Our issues seem to be only in the winter, when trying to fight heat with heat.
- Removed and cleaned the course (plastic) ERV filters, they were originally quite clogged up with dust and debris to the point it was thick as clay. Cleaning them didn’t seem to make much difference for the interior temperature though.
- I purchased a good quality infrared temperature gun to check for hotspots along the walls/floors/ceiling, found nothing significant. All generally 75-80F, close to whatever the interior room temp was.
- In the winter, hallways were fairly warm, (75-80F+ or so) and I physically taped myself inside and totally sealed all cracks around the front door to isolate this as a potential contributing cause. (As it normally blows positive pressure from hallway to the unit) No noticeable change inside. Even when opening my patio door at midnight in the spring (50F outside) to bring interior temp down to 65F or so, it shoots right back up to 75F within an hour or so.
- We tried to remove the ERV core for more thorough cleaning, but the door physically won’t open all they way. The access panel in the ceiling blocks it from opening fully. Because of this, we can only get access to one of the two fans in the ERV to remove it and dust off all the fan blades (trying to improve efficiency of airflow). We cleaned one of the two fans, the other one is still quite dusty (see photos). Hasn’t been cleaned since new construction 3 years ago.
- HVAC tech had an idea to increase the “low speed” ERV fans (when not on it’s 60 minute timer), in hope that a higher ACH might help us. He didn’t do this via air balancing, and just increased the speed by hand with rough estimates.
- Changed the fan coil filters (large ones) multiple times, ensured nothing thicker than a MERV 8 to make sure not blocking this airflow.
I noticed that in the manufacturer’s documentation, they recommend an air balancing if the airflow is low. They also recommend that the fans be cleaned annually, along with the cleaning of the course filters obviously. The tech could only access one of these fans, and said he didn’t know how to complete an air balancing. I’m fresh out of ideas and the HVAC company says they dont know what else to do. I just can’t sleep when its 80F+ in my place, and the bedroom only has a tiny window that only opens a crack, because it’s totally reliant on this mechanical ventilation.
Please toss my any ideas you might have! What questions or troubleshooting could I ask of this next HVAC tech to have them try to fix the problem in the winter?