HVAC HEAT PUMP, COMBINED UNIT.

Check the Friedrich "Vert-i-pak" units at www.friedrich.com. With scroll compressors and proper vibration isolaters noise is minimal.

I also think Liebert and other computer room AC manufacturers make similar "all in one" units with condensers ducted to the outdoors.

Thx Reid, for the input. Friedrich was closed for the Memorial day weekend, but they have some units that look promising.

"Heat Pumps" do not know where their "high side" air comes from - so a power assisted duct from the gabels would work just fine. The problem comes from winter operations in which one would have to have a means to remove the condensate and melted ice during defrosts. That is a whole 'nother problem in plumbing and complexity. Make certain that the ducted plenum blower has excess CFM, to the high side condenser/evaporator needs. Starve that and you are toast.

Definitely agree. The outside air ducting is the LAST place to skimp for this setup. Make sure there is more than enough air in and out of the unit so heat can be rejected or picked up to the outdoors.

Depending on how many you need, how about a water source heat pump on a closed loop with a small boiler and tower or fluid cooler?

Thx, Stedou73ish, but I am unfamiliar with those units. Don't I need a lake or shallow underground water supply for those units? Also, the boiler, tower or fluid cooler (in the attic?) sounds like more maintenance than this guy wants to be responsible for.

Your proposed project is too small for the added complexity of a boiler or cooling tower. You do not need a lake or water supply as the water loop is a closed circuit system.

Hi Reid, the Friedrich unit I'm looking at has an 8 to 14" adjustable duct accessory for the hot air. I would think this would be short enough?

The two small offices are in a tall metal building? What is the building used for?

A quick primer on heat pumps. Standard air conditioning uses a closed cycle with compressors to move heat from a lower temperature to a higher temperature. A heat pump uses valves to reverse the process in the winter time, within certain temperature limits.

In the summer the heat is taken from an interior space to cool the room and is discharge outdoors. In the winter time, the heat is pulled from outside air and discharged indoors. However, around 0C to 5C, the efficiency drops down and usually some type of supplemental heat is needed.

That is why there have been a couple of posts warning to keep the high side (condenser air) sufficiently large to easily exchange heat.

If temperature control in the building is under control could this space be used for heat exchange to minimize ductwork penetrations in outside wall?

Hi again Reid, he plans to build a 45' x 150' x 16' tall at-the-gable steel pre-engineered building, and divide it up into 6 separate walled, 25' x 45' rental areas, with a 350sf, 14' x 25' x 8', 2-room office area at the front of each rental area, and the rest used for storage, or whatever each tenent wants. The office areas would be built with standard insulated 4" stud walls and ceiling, with gypsum board, etc.

I'm thinking the "high side" refers to the high-temperature side during the summer? But during the winter, this same side would be the low side. Correct? Anyway, for the 350sf office area described above, I'm figuring a 1.5 ton heat pump would be more than enough, and if it puts out that much cooling, and I provide for a short duct no smaller than the louvered high side grille, I should be in good shape. What say you?

Each of the six rental areas will have their own temperature control. I don't think it'd be wise to expel the hot heat pump air into the tenent's storage area, but better to the outside, thru the front wall, above each office area, as the owner does not want to put anything on the roof.

What is the outdoor temperature in summer and winter?

Ordinarily, someone would do a heating and cooling load calc to determine size of HVAC equipment because over or under size equipment can cause unintended consequenses.

You may want to design the office roof with a load-bearing capacity, and place signs so the tenant does not overload it. It would also help the AC service tech with filter changes and service the equipment.

Good morning, Reid, the outdoor design temperature in the summer is 100ºF and the winter is 12ºF. I used the HVAC-Calc software; it came up with 16,635 Btuh Gain, and 25,752 Btuh Loss. I was thinking that using a 1.5 ton unit would provide an 8% margin of safety, while during the winter, the heat pump would put out at least 9,000 Btuh, and some 5KW heat strips would make up the 17,000 Btuh difference.

For uniform storage load, I'm using 125#/sf, from Light Storage, Item 37, Table 1607.1, p 286, '06 IBC. For the 14' span, I'm looking at S6x12.5 I-Beams, 19.2"OC, with 3/4" structural plywood or OSB 40/20 sheathing.

Dollars to donuts, someone will store stuff up there. Make sure you put signs up stating the loading limits. (but you knew that already)

Abbreviations. Would you happen to know the meaning of the following abbreviations? OBD's at all supply diffusers? HB w/VB (Hose Bibb with Vacuum Breaker?) Metering Faucets? Flushometer Toilet? Electromechanical Hydraulic Toilet? Blowout Toilet? Thx.

Hi Tinker65, thx for the input. As a novice in this area, I have the following remarks.

I'm interpreting your comment about the "high side" to mean that part of the system that expels heat to the outside air during the summer. Is this correct?

I'm thinking your comment about a power assisted duct refers to expelling the hot air from the condenser? I'm hoping to specify a heat pump such as like some of those from Friedrich that I can order an adjustable short duct, and place the unit close to the wall, so I won't be needing a power assisted duct. If you're referring to the conditioned supply air, the units I've been looking at have quite a bit of cfm.

I would have to run a 1/2" Cu line down the front of the building to drain the condesate during winter months. The owner would have to be fine with this.

How does the above sound? Thx.

Okay,

1/2" is okay on paper but go with 3/4" condensate for adequate sludge capacity over time. 1/2" drains often clog during their first cooling season. Since your winter temp design is 12 degrees, you'll likewise have to include pipe heater tape between the insulation and the drain pipe, as well with a 120 vac t'stat with remote sensor bulb to the outdoors where wind chill is a factor; also under the insulation to control the heat tapes on/off cycles. Don't let the bulb come into contact with the heat tape. (Told you there was more complexity ...).

For clarification: Granted, this is a "heat pump" so the term "High Side" which is generaly associated with a standard split system or package system mechanical air conditioner, "usually" means the condenser side of the system (except for mechanical dehumidifiers). For reduction in descriptive verbiage one refers to the coils exposed to the outdoor ambiant air as the high side, even with a heat pump - just for ease of conversation when makeing comments on hooking them up - in truth a "heat pump" uses both coils for evaporation and condensation; if you want to split hairs.

I had missed the comment about the friederic package unit - hower, if it is speced for this kind of operation - most of my engineering comments are moot. Hope the condensate advice was of help.

Good morning, Tinker65. Thx for your comments. In an effort to accomplish them, I would specify a 3/4" Cu condensate line, down the front of the building, with pipe heater tape, then wrapped with insulation, connected to its own thermostat, that has a remote senser bulb, located on the outside of the building, but away from the heater tape, and the condenser grille. How does that sound? After he sees the complexity, maybe he'll go for a split unit!

Thx for your patience and "learning me".

Yessir, you duplicated everything okay. I assum that you have no inside waste water access.

Couldn't the condensate be run to an indoor sewer with an approved "air break" fitting? This would save the complexity of heat trace on a 3/4" copper tube on the side of the building.

Hi Reid, excellent suggestion. Since the vent to the roof from the WC would be coming right past the heat pump, I don't suppose it'd be kosher to tie the condensate line into it?

Different code interpretations. Drain connection to the vent needs a deep seal trap, and approved air gap. Make a sketch and casually ask the plumbing inspector for his interpretation. I have had different inspectors give different opinions.

Good morning, Reid. That's a very good point. I'll keep that as an option. It might be less trouble to just show the condensate line going down and tying into the lavatory drain, upstream of its trap.

sell him 2 units one 1 unit over each room. 2 units would not have to work hard and the noise would be lower if any.

Thx, dadw5boys. That method also has the advantage of separate thermostat controls.

depend on the rooms size, you can use one or two heat pump window units then direct the return and supply air to the rooms.

Thx, adeeb. I will keep that in mind when I talk to the owner.

Check out Liebert or Florida Heat Pump Co. We've got both on site, & it sounds like what you need.

Thx for the tip, guest. I'll look into them.