Add-on Heat Pump with existing LP/AC system

[buswellj]

Hello,

I work from home as a software engineer, and last year I added a 300 sq.ft computer room/lab in my basement. The room is not connected to the existing house HVAC system. Currently the room is cooled by two Fujitronic 13,300 BTU Portable AC units, and 750 CFM duct booster fan that is temperature controlled (designed to pump cool air in from the outside to take the load off the a/c units when the temperature is below 60 F outside). This works fine during the cold winter months here in Ohio, but as the summer approaches I know I'm going to need something else.

I have talked to a couple of local HVAC contractors, but they want to replace the outdoor AC unit with a heat pump rather than adding the heat pump to the system. The existing outdoor AC unit is efficient at cooling the rest of the house, so I don't want to really replace it since its brand new.

I wanted to get some advice on whether it is safe and practical to add-on a packaged heat pump (such as the Goodman 5 ton 11 SEER model) to the existing system. The heat pump would supply two zones, new ductwork in the computer room (1), and duct work that adds the heat pump to the existing supply/return for the rest of the house (2). Should this work? Are there any safety or other issues that I should make sure the HVAC contractor has factored in to prevent equipment damage etc?

During the summer months, zone (2) to the rest of the house would be closed, and the heat pump would just cool the computer room.

During the winter months, the supply to zone (1), the computer room, would be closed, and the heat pump would heat the rest of the house until the outdoor temperatures dropped below efficiency levels for the heat pump. At that point the heat pump would shut off and the LP furnace would take over.

Is there a better way to use the heat from the computer room to reduce the load on the heating system?

Thanks

[james mo]

If you combine the house and the lab together, you will not be able to tag in a second system. You would probably be installing a larger, 2-stage system with a zone control. You could duct in your outside air as first stage cooling with an outdoor temperature or enthalpy control to reduce your cooling costs during mild weather. You can also run continous fan to distribute the heat from the equiptment to the rest of the house and install thermostats with automatic changeover feature in case the house overconditions due to the heat generated and recirculated from the lab. My recommendation(based on what I have read) would be to install a dedicated cooling system for the lab. Sometimes, we have a tendency to over engineer systems to increase efficiency and later find out that the system becomes unreliable. Since you have a newer system for the house, you could leave that one alone and install a simple and reliable system designed specifically for your lab's needs.

[beenthere]

Like James said, leave the house alone, and just install a system for the computer lab.

[docholiday]

I agree, the loads are too different for a single system to properly manage even with a zoning system. You may find you need cooling in the fall and spring when the rest of the house needs a little heat here and there. Besides you would have to replace all the ductwork if you upsize your current system.