Problem with Integrated ERV Forced Air System
Our new one-floor condo unit in the Boston area (Zone 5A) has an integrated ERV Forced Air System, and we’re having problems with air supply in our bedrooms, similar to that discussed in the GBA article on integrating an ERV or HRV into a Forced-Air System. Our ERV is a Reversomatic RERV-D100 (which runs continuously at the lowest NORMAL speed setting) connected to (we think) a Samsung AMxxxMNMDCH/AA Heating/Cooling unit. The input to the Samsung unit comes from a collector box (air plenum), which mixes outdoor air brought in through the ERV with room air pulled in through the grille of the collector box. The Samsung unit output is then distributed via ducts to supply vents in the main living space and the bedrooms. Exhaust vents in the bathrooms are ducted back to the ERV to be exhausted outside.
The problem is that when the thermostat isn’t calling for heat, the fan in the Samsung unit doesn’t seem to run, and all the air supplied from the ERV is dumped out into the room through the collector box grille instead of being pushed through the Samsung unit and distributed throughout the unit, which leaves the bedrooms feeling stuffy, especially when the bedroom doors are closed. This happens regardless of whether the thermostat is set to AUTO, or to HEAT (with a speed of either LOW, MEDIUM, HIGH or AUTO)
The Samsung manual at https://s3.amazonaws.com/samsung-files/Tech_Files/DVM/DVM+S/Technical+Data+Books/Sequence+of+operation/DVM+S+Sequence+of+Operations_V1.2_12202018.pdf seems to indicate that there’s an internal LOW LOW fan speed available, but I’m not technical enough to understand whether this means that when no heat is being called for, it might be possible to set the Samsung unit to run at this LOW LOW speed, which might avoid dumping the supply air through the collector box grille, and distribute enough air through the bedroom supply vents to avoid the stuffiness in the bedrooms.
If it’s not possible to have the Samsung unit run on LOW LOW (or at worst, just LOW, albeit more expensively) when no heat is being called for, I’d be very interested in other advice about how to address the problem at a reasonable cost.
BTW: The original construction documents for the building had the same design, but specified use of Daikin components, so I’d also be interested in hearing whether the Daikin components might have been able to be set to avoid the problem we’re having.
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Replies
It sounds like you have a dedicated ERV exhaust system but not supply. A hybrid ERV ventilation. And the ERV is not interlocked to the furnace. So when the furnace is not on air comes out the furnace return vents. This is by design, or at least it would have cost more money to create a separate ERV supply line.
You can solve this by running your blower 24/7 on low speed. If you have a high efficiency furnace than the electricity cost should be minimal. However, there is a humidity penalty to running the fan continuously when the AC runs. To solve that you would need to have some kind of interlock between the ERV and the blower and it still might not work perfectly. See this Q&A https://www.greenbuildingadvisor.com/question/avoiding-the-erv-humidity-energy-penalty-when-connecting-to-existing-duct-work
Unfortunately, the problem we're having is that the Samsung blower turns off when heat isn't being called for, and I don't have the technical chops to determine whether what it would take to get the Samsung's blower to run at either LOW or LOW LOW speed in that case.
Your thermostat should have a setting to run the fan.
It looks like you are linking to a manual for a heat pump but not an actual air handler.
I'm not familiar with Samsung units but on others this option is set on the thermostat in the installer menu. You'll have to figure out how to get in there and which setting to change. This should be somewhere in the manual of the unit or the thermostat.
What you are looking for is thermo-off fan setting for heat. Sounds like it is currently set for OFF, you want to set it to low or low-low.
Another option is the indoor units usually have a fan on dry contact input. An HVAC tech can connect this to a timer to run the fan to mix the air in the house. The only issue is this is not like a standard hvac with a G terminal so they have to check the electrical diagram for the unit of where you need to connect. Try to find somebody that knows Samsung ducted units, most likely commercial installer.
Thanks