HVAC Unit in Attic

Typically a Heat pump would give you about 3 times the electrical energy used in heating and also cool the home. THis would be a split system with the condensing unit located at ground level, for service and noise isolation.

Be sure to have a good drainage pan and water detection switch since its in the attic.

Take a look at LENNOX online for more details of the units available and their features.

There are split systems that have no ductwork that hang on the wall and can service several units/rooms for smaller homes. They are called ductless and provide some unique benefits, look at SANYO as one supplier of such units.

Be smart and get programmable thermostats to save 15% OVER a standard thermostat due to setback operation.

ENJOY< Woody

OH BTW high efficiency units qualify for a 30% tax credit up to 12/31/2010. This is up to a total of $1500.Woody

The client wants to use an air cooled ac unit with a furnace. Can a packaged AC Unit like that of (york, carrier etc..) be put in the attic.. How does one handle outside air (louver?).. Exhaust is required in the attic.. how does one handle the return air (directly ducted to outside or mixed with attic air and ducted outside) Thanks

A unit for a motel is described as a PTAC

the size is standardized

You will need a Split unit with the Condenser unit outside somewhere away from the attic. the attic is going to get hotter than a firecracker and the condenser unit won't be able to dump the heat generated into the attic because the heat differential will be relatively low. plus all that heat will want to try to find it's way back into the Conditioned living area.

Typically the furnace is also the air handler in the system and the air is pulled in through filtered intakes in the house, you may need more than one intake to keep from starving the system for air and to help balance the airflow. the blower blows across either a heat exchanger (for gas fired furnaces) or heating elements (for electrically heated systems) and then over the evaporator coil of the AC system, and from there it enters a conditioned air plenum where it is distributed through insulated ductwork to the living spaces. Obviously only the coil or the heat exchanger is operating at one time in such a system. the condenser and the compressor part of the slpit system is connected by copper tubing to the evaporator coil . the condenser/compressor is usually sited outdoors where there is lots of airflow, either on a roof, or on a concrete pad at ground level for servicing convenience. The design and sizing of this sort of system is not something an average DIY homeowner can do himself, a qualified HVAC system person needs to be doing this sort of thing. Also consider adding a small filtered outside air intake into the system to help pressurize the living space so that the system does not suck dust and pollen and such into the living space through uncontrolled openings like cracks around windows and doors and through wallspaces and such. generally you want the living space to have a positive pressure with regards to the outside air. It is healthier to lose a very small amount of filtered/conditioned air through those uncontrolled openings than it is to suck dirty outside air in through them. The cooling/heating efficiency loss is minimal and it is much healthier for the occupants.

Agreed - Any restriction in air flow to the condenser is a negative.

Vibration could be a real problem - few wooden structures are going to take any without creating a problem. This is a problem with any turbine attached to a home - just plain a bad idea.

The entry point to an existing air system has to be into a duct at the 'right' point not to create flow problems.

OH BTW, What does that stand for? Sorry!

PTAC means Packaged Terminal Air Conditioner- basically the equivalent to a rooftop unit, only smaller capacity and mounted in a wall rather than on the roof. They are typically single stage cooling with electric heat, although some higher grade models may be heat pumps with back-up electric heat.

OH BTW = oh by the way

I mis understood the OP's [original poster] query to be along the lines of:

how do I keep my attic warm & cool?

as if it were a living area

I hate abreviations! Sorry as you can see I am not an AC expert. The reason I got into the discution was because I had tought of using such a unit for my home. The only difference is that I would like to have an AC unit installed on the roof. When I saw that "OH BTW" I thought it was some kind of AC unit code. Please don't laugh, now it is funny to me too, I thought OH had to do with water!

If your client is looking for the "best" value- they should use a ground-source heat pump (geo-thermal) that will generate the highest tax incentives and the lowest operating cost and the highest life and the quietest operation.

Several contractors are qualified- so have the client get MANY bids because prices charged can vary dramatically. All systems should include a minimum 5-year warranty on refrigeration systems.

Be sure to include a 7-day, minimum 4 cycles per day, individually adjustable thermostat AND a humidifier- either in-house or at the return inlet connection.

Humidity moves very quickly from its point of production to any "dry" area, so the in-house style would be the most easy to maintain (and the least expensive). Maintaining higher humidity during winter months will allow lower room temperatures (and lower costs) PLUS reduce the risk of colds and flu.

Heat pumps are great. But they do not work well in areas where the winter temperature can get as low as -8 deg F (like this one). One would need a back up source of heating and that cost eats into the heat pump savings. I decided to use a packaged rooftop AC unit with gas heating. Thanks for your help.

Unless you are in the far north where an ASHP (air source heat pump) is not efficient in the winter the ASHP will always be more cost effective than a GSHP (ground source heat pump).

If your electric bill is 100 USD then with an ASHP having a COP of 3 (min) the elec bill is 33 USD and the GSHP that may have a COP of 4 (max) the elec bill would be 25 USD.

The 8 USD difference will never pay off the additional costs associated with the GSHP plus they are over priced as of yet anyway. The ground loops or wells are not cheap!

In areas where winter temperatures are too low for an ASHP then I definitely agree.

The real OPERATING value of the GSHP system come in the summer.

COP (which stands for Coefficient of Performance) deals with the amount of thermal energy delivered per unit of input energy- since GSHPs have a "warmer" source of energy to draw from, they can provide higher output with the same input- hence higher COP during the HEATING season.

During COOLING operation, the efficiency measurement is called SEER (Seasonal Energy Efficiency Rating). For several years, the US minimum SEER for split-system air-source heat pumps (or just cooling only units) was 10.0. In 2006, the new minimum changed to 13.0. Energy Star models start at a SEER of 14, but are usually 14.0 to 16.0. That extra "boost usually nearly doubles the cost of the system components. GSHPs often have a SEER ranging from 26.0 to 28.0 (some are higher) because, rather than discharging their waste heat into 95F AIR with a coil, they discharge into 50F WATER through a heat exchanger.

Because of that "cooling" added value, the cost to cool your home will be about half of what it would cost for even an Energy Star system.

When you add a refundable tax rebate of 30% of the cost into the mix, and you can find an installer who is not trying to retire before he is 45 with the money he is making from GSHP installations, the payback is pretty attractive.

When you add the extended life and reduced maintenance factor (no leaves in the condenser to clean, reduced loads on the compressor, reduced need for booster heating) to the mix- GSHP is definitely the way to go, especially if this is a new home installation.

By the way- another post discussed the elevated temperature of the attic. Be sure that ALL ductwork in the attic (supply AND return) are well insulated. The air handler-fan coil will likely already be insulated, but- if not- insulate it as well. In addition- install a thermally-triggered attic exhaust fan with eave vents to hold attic temperatures within 5F of ambient (set the trigger thermostat for 75F). This will reduce thermal heat gain INTO the house as well to lower operating costs.

Who woulda thunk that is what COP & SEER stood for!

Considering I didn't turn on the AC this summer the supposed benefit would not been of much value. The average high for August was 33 deg C and the average low 25 deg C.

Can you give a reference for a heat pump supplier offering a SEER of 26 to 28? I would like to look it up.

If one studies the costs and performance in a mild climate there is no way a GSHP can be cost effective for reasons I mentioned previously. All the tax breaks you mentioned for the GSHP are also available for the ASHP systems are they not.

Another factor is that GSHP units have a much more questionable reputation as of yet.

I did not check actual ratings- just projected what SHOULD happen with 50F water vs 95F air and did not realize what crap is currently being sold because Uncle Sam lets them get away with it.

Current Fed minimums are EER of something like 16.2 for OPEN water-to-air units, they climb in 2011 to 18.1 and again in 2012 to 21.1. SEER readings are usually about 30% higher than EER, so- by 2012, the SEER should be about 27.4. The current 16.2 is only 21.

A Google search of "geothermal heat pumps" did come up with the Econar brand that provides 10-year warranty and has VARA plus 2 model (multi-speed compressor and fan motor) that has an EER of 22.8 (SEER of about 29.6) using heat sink water of 67F, so you can find my "goals" out there.

Lots of things SHOULD happen! Some do and some don't.

Itg seems to me, mounting an air conditioner heat exchanger in the attic is not a very efficient way of doing things. For a number of reasons, the attic is going to be the hottest area around. The air conditioner is throwing heat away. Trying to throw heat away into the hottest ambient conditions does not sould like a viable solution. You want to blow the collest air you can find over the heat exchanger to maximize its effectiveness- and you aren't going to find that cool air in the attic. If on the other hand, one's primary energy consumption is heating rather than cooling, ignore everything I have said so far...

If the building is designed correctly, the attic should not be that hot. Unfortunately many, in fact most are not designed correctly. The goal is to have the attic temp as close to outside ambient as possible. You accomplish this by installing radiant barriers as close to the underside of the roof as possible so that radiated heat which is close to 60% of the heat input is reflected away before it can heat the attic air. the attic should be well ventilated so that what heat does make it in is quickly carried back out via either convection or forced air ventilation. continuous soffitt vents and ridge vents work well for many roof types, but some roofs must used forced air ventilation to achieve this.

If you are installing this heavy HVAC unit in an attic, give some consideration to the strength of the attic. The fan running up there can loosen existing structural members. That can lead to cracking of walls and ceilings.

If there is a load bearing wall that it can sit on, that would be best. Under fire conditions, roof mounted devices tend to drop it the worst time.

We have a facility that has the furnace/blower units in the attic and the condensers are based outside where the heat dissipation, noise, weight and vibration are no longer a problem.

What will make the installation harder or easier also depends on the pitch of the roof, where power can be attained, gas lines for the heating mode and access to the attic area by way of a pull-down stairs that has the capacity to carry the weight of equipment and service guys who may be, shall I say "stout".

Whatever type unit you put into your attic, the first time it snows, you will probably have a problem. Attic mounted units tend to make a warm spot on the roof above them. This melts the snow, which runs down a few feet, then freezes again, resulting in "ice dams" which wreak havock on roof drainage and soffit areas. If you go with a unit in the attic. Box it in with insulation board, and have a vent in the box bottom and top, which draws outside air in, and allows hot compressor air out, preferably a thermosiphon system, where cool air enters from the bottom, and hot air is vented out of the enclosure and attic via a vent pipe to the ridge vent or out through the roof.

Thanks a lot for your input. I thought I made a post yesterday but I don't see it on the list. Thats strange. The units are now going to go on the roof... Also, how do you calculate the savings in using a heat pump as opposed to using a gas furnace..

You mean this post?

No, I had another one. I probably forgot to hit submit after previewing