Mini Split Heat Pump Question

[xtahoex]

I searched on goggle and found this site but did not find anything that answered my questions. So, here goes. I just built a 36x60 gambrel barn styled workshop. The 1st floor is all work space with 14' sidewalls it is neither heated nor cooled, it basically at the ambient temperature of the day. There is a complete 2nd floor that I am currently finishing up. My wife will be moving her office up there along with a studio apartment for guests, a workout room, and a storage room. The office, apartment, and workout room are all going to be insulated to code and I am deciding on how I want to heat and cool the space. I was thinking of going with a zoned traditional heat pump. I then started looking into the mini split systems because of the features and efficiency.

Here is the question. The structure is permitted but the upstairs area is not. I want to do my best to keep the 2nd floor space stealth. So, I was thinking of mounting the compressor on an interior wall downstairs with the exhaust air vented to the outside of the building via an approx 24"x24" vent that will be as air tight to the unit as possible. I don't think the exahust is going to be a problem it is the fresh air that I am concerned about. It is a rather large space in the first floor that is wide open (30K ft3). The main barn doors that I created are a bi-folding door and due to their nature are never going to be airtight, which for this application may serve an advantage in creating fresh air for the a/c unit. This inside location would also serve as a benefit to create shorter runs with the supply lines. The unit is only 63 decibels so overall it is very quiet.

I just wanted to get peoples feelings on this. The other option I have is to install the unit on the outside of structure high on a wall under a large lean to. I just think it would be very ugly in that location versus a painted exhaust gill.

I understand this is not a traditional setup and I am not looking to get flamed for it... just some honest advice.

Thanks

 

[xtahoex]

Anyone?

 

[pseudorealityx]

You can duct the make up air too. Do NOT undersize that ductwork. The big prop fan in a condensing unit is not designed to have to fight against any static, so oversizing is a must.

 

[DPelletier]

The condensing unit installation instructions will have minimum required clearances shown. It is obviously meant to be installed outdoors. In order to have it inside and duct it, you would need positive air movement in the enclosure equal to or greater than the rating on the condensing unit's prop fan.

...short answer, put it outside or put it exposed inside an let the heat bleed into the space...you could add a general exhaust fan (and associated fresh air intake) to then remove the excess heat from the lower space using a reverse acting thermostat.

Doing what you propose is certainly contrary to the Manufacturer's instructions and would void any warranty you might have.


Dave

 

[xtahoex]

The "duct" that I am proposing is really nothing more than a hole framed into my wall covered by a return style air grill. The unit would literally be mounted against the wall with a gasket built around it to shroud the exhaust air. It would be interesting to see how much pressure that would cause.

I also understand that I am taking a risk with the warranty.

 

[DEnd]

Yeah don't do that.

The issue isn't really the amount of pressure the duct may create, the issue is it will either be drawing from a negative pressure zone or pushing into a positive pressure zone. Those fans are designed for basically free air circulation, by enclosing one side of the unit you create a pressure difference above which the unit is designed for. This reduces air flow across the coils which results in a lower efficiency of heat exchange from the coils. This will in turn cause the unit to not operate correctly.

All that said, get the structure permitted and fully inspected, if something happens and there is unpermitted and uninspected work done to the space your insurance company will deny your claim. Also if unpermitted work is found during a home inspection it can cause possible buyers to not be able to get a mortgage on the place.