First of all I want to say thanks for this site. I have been searching and reading all morning on various topics but have not yet found my specific problem so here goes.
First I live in Chattanooga and recent temps are hovering around 95-98 during the heat of the summer.My house was built in 1997 and was built to the local power companys ENERGY RIGHT program. Low E windows, house wrap, insulation between each floor etc.
I have a 2000 sq foot basement (un heated but dehumidified and since it is a lot under ground it stays 65F year around and I keep humidity at 50% to keep tools from rusting etc.
The main floor of my house is 2100 feet and runs off a bryant 3 ton Heat pump split unit. It keep the house perfectly cool and all the duct work is in the basement so of course it is cool too. Discharge air at any vent in the house is 49-51F and my total all electric power bill runs under $200 year around.
Upstairs I have a bonus room(S) of about 700 feet total. The roof rafters are 10" and they have R30 in them with the foam inserts for venting, I have a full ridge vent and full vented soffit all the way around the house. I have two gables and one contains a power fan of 1620CFM. The 10-12 pitch roof faces full west exposure and the BLACK shingles result in attic temps of 125F in peak times even with all the soffits open etc.
The unfinished part of the attic has loads of blown insulation and none is blocking the soffits. And the main problem as you may have guessed is the bonus area stays HOT. In the peak I see 76-80 degrees from the 1.5 ton 12 seer Bryant Heat pump split unit. Basically the same unit type as the main floor except smaller in size.
IT has frozen up once or twice over the last 8-9 years but it is rare. I did check the discharge vents and noted that the airflow from them on my annometer is quite a bit higher than the main floor. 550 ft/min vs 350 ft/min downstairs. Could that indicate insufficient ducting?
The freon lines have a long run to get upstairs because they run up through a chase in the basement. Also the air handler is in the attic so I have been spending the last few years double wrapping the flexi return duct with another larger flexi duct as well as wraping the main trunk (hard line) to keep what btus I have in the ducts and not in the attic.
I have had the local power company out to evaluate insulation and the units output. They did some wetbulb tests and confirmed the unit is putting out about 16-18kbtu. Heating in the winter is never a problem at all.
I have been checking air in vs air out temps at the air handler and the farthest vent and I see the air is still picking up some heat in the attic but due to the shape and layout of the attic all the ducts have to run on two sides of the attic so at least one of the flexi runs is long and a requirement due to space restrictions and layout.
At night after the attic cools off in the attic the unit does low 50sF discharge. But in the day the farthest output duct is only 68F into a room that is 78.
I have spent days and weeks sealing up duct leaks, over insulating everything, venting the attic etc.
I even added a portable AC unit of 10K BTUs and while it helps it is still not enough (it does have outside water drain and air duct to exhaust air.
At this point I want to install a new unit but I assume I need something like 2.5-3 tons. I have called three different places and none do real load calcs. They just say " 1.5 ton should be enough for 700 square feet. But yet in my SE USA location nearly every bonus room I go into is WARM in the 95 degree days. I also assume my current freon lines and air handler are not big enough nor will the main air trunk. So I am basically having to start over.
I need to get the room down to 72 min for a new home theater/office so I am trying to get some tips on what to do. Basically I am going to just hire someone and tell them what I want as they dont seem to have any qualified people around here to properly size it. Or at least I cant find them if so and I have two close relatives in the HVAC business and this includes them.
And humidity is pretty good up there with it staying in the 50% range =,- 5%.
Anyone have any tips or sizing questions?
Thanks in advance for your help
[Edited by rotts4u on 07-03-2006 at 09:57 AM]