High velocity AC or Mini split
Hi all. Looking for some advice on adding a cooling system to my house. I have a 1500 sq ft earth home that is made almost entirely of concrete so conventional systems most likely won't work as there is no good way to run a supply and return air line. I am looking to cool 4 rooms: 1 23'x23' living/kitchen area, 1 13'x13' bedroom, 2 9'x 13' bedrooms. All the rooms are located on the south wall of the house and each room has a large window. The south wall of the house is wood and is well insulated. My initial plan was to install a mini split in each room and run the line sets through the outside soffits. During my research on split duct units, I found another possible option, the High velocity systems. Does anyone know if these systems work as they are advertised? How do I go about finding a reputable contractor in my area, ie. what questions should I ask. This house also has a problem with humidity. It is sealed up so tight as well so the air quality in the house gets bad during the hot summer months. Would either system help alleviate this problem?
I would look at Mitsubishi Ductless - great de-humidification and you get zoning and complete control for each room.
You can have 4 indoor units attached to a single condensing unit, with the mini split. Cost of installation would be something to look at. as far as SEER goes....the mini splits will blow the hi velocity system out of the water every time.
If I go the mini split route I will definetley be going with the mitsubishi units. I have heard nothing but great things about them. High velocity is out. I had a estimate done for a conventional unit today, just waiting for the price to come back. I live in an earth home and there is no way to run duct work through my house except through the front soffit of my house. I had previously thought the area was too small but when I tore the soffits down I found there is just enough room for a 8x14 trunk line. The guy I had do the estimate is planning on running triangular shaped custom ducts with insulation inside. The other option is to run the 8x14 but I would have to insulate the soffit area. I like option 1 better. Any thoughts on this?
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Last edited by jpsmith1cm; 08-02-2012 at 05:58 AM.
Reason: Non-AOP member
Careful on the sizing. All that thermal mass will greatly reduce your cooling load. Although Minisplits can be oversized a little and still dehumidify well but you still want the condenser to have long run times.
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What are going to do with all the copper lines to connect all the sections of the mini splits.Don't forget about drain lines.
1/2" to 2" holes aren't hard to drill through concrete.
The south wall of the house is wood stud walls and the top parapet wall is hidden by a fake roof that will have 8" facia boards. This alows me 7.5 inches of area to either run 7" ducts through or line sets for the the mini splits. The only thing I am having an issue with is that the drain lines on the mini splits will poke out through the house below the soffit area. It is either that or I will have to get units with pumps on them to pump the water up and out. That will be an added expense I'm sure. Still waiting for the estimate to come back on running the custom duct work through the soffit. I think at this point we are leaning toward the conventional type setup. Does anyone have any tips on sizing a unit for a house such as mine? I now it can't take nearly as much to heat and cool this place as a standard home. There are only about a dozen earth homes in my area so no one seems to know much about them.
What is the consumption history? How is the home heated?
Is the soffit indoors or outdoors? (Don't put ductwork outdoors.)
Why did you abandon the hi velocity idea?
How will return air be handled?
Why are you leaning towards conventional?
Have you tried running bath fans to improve air quality? Does it help?
Which makes more sense to you?
- turning your thermostat back and being uncomfortable. Maybe saving 5-10%
- leaving your thermostat where everyone is comfortable. Saving 30-70%
DO THE NUMBERS! Step on a HOMESCALE.
What is comfort? Well, it AIN'T just TEMPERATURE!
Energy Obese? An audit is the next step - go to BPI.org
, or RESNET
, and find an auditor near you.
I have done alot of earth/berm homes. The cooling load is low. What is the cooling load on the home? Climate? My experience is not enough cooling load to dehumidify. Keep the a/c small.
Originally Posted by burhead
Also a ventilating whole house dehumidifier (Ultra-Aire) is a must. This will get the filtered fresh make up air and moisture control that you must have for comfort and indoor air quality. There is a new 1 ton version for hot climates that has a remote condenser and mostly latent cooling with a little sensible cooling.
let's talk (post).
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
mOk first off a little more about the house. The house is a pretty standard earth home layout. It is pretty much a ranch syle house buried in the ground. The living/dining/ kitchen is all one quadrant of the house (approx. 24x24). The other 3 rooms of the house are a master bedroom (13x20) and 2 smaller bedrooms (9x13 each). All of these rooms are on the south wall which has a fake roof that mainly just hides a parapet concrete wall. The roof/ soffit area is un heated and uninsulated. There is enough room inside of this area to run an 8x14 rectangular duct and then drop out and into each room with 7" pipes for registers. I was given the option of running 8x 14 duct and then insulating the soffit area or running a custom triangular shaped duct with insulation inside of the duct work. The triangular duct would be larger to allow for the interior insulation, though size wan't specified. The house is currently cooled with a through the wall heat pump and it serves well 11 months out of the year. The house is heated with a wood stove and base board heat in the bedrooms. We are comfortable most of the year. We have a toddler now and the wood stove will not be used as frequently. The main reason for the HVAC upgrade is a new addition on the house. We added a garage with a second story. A bedroom and bathroom will be going in the second story of the garage. The upstairs bedroom will be 14x20 and a small bathroom as well. This area has a conventional roof and is above grade.
The return air will be "wild". I know this isn't optimal but we really have know other choice if we go with a conventional heat pump.
I ditched the high velocity system because no one in my area is experienced with them. I would hate to pay 2x the money and have a system that doesn't perform properly.
I am considering conventional mainly because it is what most people know and want to install. I never thought it was possible befor now. I like the mini splits but I think they will cost more and I think the astetics would be a turn off to some.
I live in Iowa. The winters are cold and the summers are humid. Temps in the winter as cold as -10. Average winter temp is probably 10-30 degrees F. Summer temps are usually 85-100 in july and august with high humidity levels. This year has been really hot but the humidity levels have been low. Running the AC unit in the living room for about 5 hours a night keeps the temps in the house in the upper 70's.