I would like to know if any one has any comments on increasing the efficiency of a split unit system. I haven’t built many homes on slabs, and I will soon be starting one. I would like to raise the unit in the attic to increase the amount of insulaiton under the unit. I would also like to know if anyone can offer comments about increasing the efficiency of the unit by increasing the insulation around the duct work, and increasing the ventilaiotn in the attic space…..what will help and what is a waste of time????
thanks
tlstewart
Replies
See this is your first post, so Welcome.
Adding a bio with location help immensley for questions, esp. about heating and cooling. (double click on your name in any heading)
Assume by 'split unit' you are talking about a heatpump/AC system, with the air handler in the attic?.
If so and used primarily for HP, insulating the compressor and high pressure side Cu pipe, accumulator, and reversing valve also helps. Best to have the airhandler in heated space for primarily HP applications, so, dont raise it, simply add insulation all around. You don't want to cut any tubes like one of my neighbors did to move a unit (big EPA viloation if caught plus $$ to reconnect whatever) unless you have the equipment to evacualte and recover the freon or are having it done professionally.
Insulation always helps efficiency. Insulate the entire air handler and 100% of the ducting, would be best for efficiency if the air handler were uninsulated and in the living space.
Thank you for your comments!
I'm not used to talking homes to folks across the nation, I'm sorry for the lack of geographical info. The home will be built in Western Kentucky, the heat and humidity together can be hard to handle here in the summer. It will be on a slab with the unit sitting in an atic area of about 4284 cu ft. The living space with the exception of one bedroom will all be on the bottom floor. The unit will sit on trusses(beam under the unit) which was the reason I was wondering about lifting the unit, to keep insulaiton consistant over the living space below. I grew up in a home with a split system, and it was difficult to keep the home comfortable in the summer months, that may have been due to the year in which the system was built and the lack of technology available. I will be living in this home and would like to keep myself cool on those hot summer days. Many people in this area are opposed to the units in the attic citing the damage done by condensation leakage and their tendency to loose cooling power. My thoughts are if the system is installed correctly and insulated properly it should work fine, I just want to get all I can out of the unit that is installed.
What do you think?
Lifting an attic mounted unit up enough not to interfere with the envelope insulation is not a bad idea, nor is insulating all parts of the system exposed to a non-conditioned environment. Neither of these will change the efficiency of the the system. Properly insulating exposed duct will reduce unintended losses, but that's not the same.
Best bet is always have the equipment inside (except fo the condenser unit obviously). And really, who can't give up a 12 or 16 sf space for furnace/air handler in the space?
I too would consider making the attic a part of the conditioned space, as is advocated by the building science articles referenced above. In fact, if I were you, I'd spend a couple of hours reading all the good stuff they have on their website, then buy their builders manual for your climate. Well worth the money, IMHO.
In our home, we insulated all exterior walls and rafter bays with a combination of Icynene and Corbond. By making the attic a part of the conditioned space, your AC efficiency will jump quite a bit because the duct losses will drop dramatically... there is a lot of heat gain potential in a 110°F+ hot attic vs. one with only 80°F or so ambient conditions. Plus, the wood works less, there are no entrances for critters to explore, etc. The building science research showed lower electrical bills for the family with the insulated attics vs. the ones with conventional ones.
The only area of concern could be that the roof deck may become warmer as a result of the underlying insulation. If you have a lot of hard sun in this location, the life of your roof material may be reduced somewhat. This apparently is more of a concern in places like AZ, NV, etc., especially when tar-based roof shingles are used. We used a fake slate product called Duraslate that should scoff at any conditions that Boston weather conditions can throw its way.
You did not indicate where you are or any details of construction. But the best option is to "move" the system (air handler and duct work) "inside" the house.
The way to do that is to make the attic conditioned space.
http://www.buildingscience.com/resources/roofs/default.htm
http://www.buildingscience.com/housesthatwork/default.htm