Fresh Air Intake location on Ducted Mini Split (Slim Style)

jb9

Hello,

I can't seem to find much detailed information about where a fresh air intake "knockout" would be located (if one exists) on these models (Mitsubishi, Fujitsu, Daikin). Do these knockouts enter before the air gets conditioned or after? Also, if a unit didn't have a knockout, would it void the warranty to install one? (My gut tells me it would be a bad idea). If I opt for a bottom configured return plenum, would it make the most sense to have a knockout or port on a return plenum section so that the fresh HRV air comes in at this location so that it can be conditioned?

I guess I am just having trouble finding the mfg literature that shows the fresh air intake capabilities. If all the air handler units are intrinsically similar in construction, I am just trying to plan for routing the HRV supply of fresh air into the unit.

Thanks.

hvacfreak2

On a ducted unit you would enter on the return duct I'm guessing. I have not seen any provisions on any that I have installed.

jb9

Thanks for the suggestion. I drew a picture to describe what I am envisioning should the unit not have a fresh air intake port. Does this look like a reasonable solution?

hvacfreak2

That is how I see it.

Are you treating this outside air with an erv ?

jb9

Yes. The outside air coming in will be treated by an ERV that will be sitting in the basement. My goal is to keep as much of the mechanical in the basement to reduce noise and vibrations that might disturb the bedroom occupants.

hvacfreak2

Sure seems like a lot of ductwork to me. Why the need for oa anyway ? I'm sure you feel that you have a reason , but keep in mind the fact that 99 percent ( or some high percentage ) of residential dwellings do not have mechanical or even controlled means of outside air ventilation . And I am aware of the benefits of positive pressure in the structure IF the structure will allow it versus the amount of oa required to achieve it. Anyway , I would try and keep it close to the equipment served and address the noise as required.

njtommy

I wouldn't be worried about noise of the hrv the couple that I have seen are super quiet. I would put it up in the attic with the ducted ahu. Aren't you going wall mounts for the down stairs any way?

jb9

Good point njtommy. I was thinking about putting the HRV in the basement, running a couple supply registers to the 1st floor and then run some of the flexible tubing (was looking at the Zehnder Comfotube at 3" diameter) up to the 2nd floor. Some folks have cautioned me about the controllers of the HRV not being synchronized with the Ducted AHU and even a possible voiding of the warranty should I choose to do something like that. I guess I may have to run separate tubing to the bedrooms (supply) and pull stale air (return) from the bathrooms. I guess I was naive when I thought I could try and use the duct work from the AHU. I heard someone say that I could bring fresh air into a ducted AHU and I saw something in the Fujitsu literature that seemed to imply it was possible. I never really saw a "knockout" in the side of the units so maybe I was mistaken. Just trying to find a good solution that is simple. The site won't really be a problem in the non-heating months (i.e. windows can be opened and prevailing winds will be nice).

njtommy

I think Panasonic has one that's stand alone and also highly adjustable for your needs.

jb9

Thanks njtommy. When you say it's adjustable, what settings are adjustable? I'm not really familiar with Panasonic's line of ERVs so I will have to take a look. Thanks for making suggestions.

Jack

I'd suggest caution in tying into the mini-split. You can do it on the AH units, but be aware that they has very little static capability and cannot handle much ductwork. On the wall units, you can influence the thermostat. The actual sensing thermocouple is on the evaporator coil. I think you would be best to keep the systems separate. You aren't talking about a lot of fresh air if you are doing it with 3". Find a place in the space where you can introduce the fresh air and enjoy the serviceability and diagnostic simplicity of separate systems. I think without direct guidance and approval of the mini-split manuf you are asking for trouble.