HVAC duct strategy

Started by MushCreek, July 06, 2011, 03:52:15 PM

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MushCreek

I know a lot of you don't do anything as citified as central HVAC, but I figured someone might have experience. As I sharpen the pencil on a final design, I'm trying to figure out the best way to put in my duct work for the HVAC. A few things- I'm smart enough to NOT put it in a hot attic, unlike millions of homes here in FL (D'oh!) I'll have a full basement, which is where the air handler will go. I see two options: Either put the duct work in the basement, which would certainly be easy, or put in a drop ceiling, at least in part of the house to house the ducts in somewhat conditioned space. The basement temperature (un-conditioned) will be about 55 for a winter low, and 75 for a summer high. That cool basement will be a plus for A/C, but a little bit of a loss during heating season. Being SC, I believe that cooling will be more expensive than heating on an annual basis.

Does anyone know the differences regarding floor registers and ceiling registers? Seems like ceiling registers would be better for cooling, and the opposite for heat, but I have no idea if the difference is really significant in a well-built and insulated house. Floor registers need to be carefully placed so that they are not likely to be blocked by furniture. The drawback to ceiling registers is finding room to run a main trunk up to the ceiling. As I said, if I go the ceiling route, I would make a drop ceiling to conceal the ducts. Since our decor will be vintage, a chase for the ducts would look out of place. I figured that I could build the house as if it were a 10' ceiling, install the ducts, and put in a dropped ceiling to hide everything. Alternately, the center 'core' of the house has a walk-in closet, a hallway, two bathrooms, and the foyer. I could drop the ceiling throughout that area, and have registers in the walls of the adjacent rooms with full height ceilings.

There is a third option- mini-splits, or ductless A/C. The house is essentially 3 rooms, not including halls, bathrooms, and closets. With careful use of the thermostats, we could probably save some money that way, too. Decisions, decisions! Any thoughts?
Jay

I'm not poor- I'm financially underpowered.

Native_NM

We did a drop ceiling on a commercial building with a wall mounted commercial unit.   One main trunk with registers branched off. 

I'd do floor registers if it was possible.  They are more efficient and result in less waste if you plan on installing the system in the basement anyway. 
New Mexico.  Better than regular Mexico.


Tickhill

We have a full basement and my first floor air handler is in the basement with main trunk running below joist level and the individual registers are fed from insulated duct (round) laid between the joists. I live in NE Missisippi and have found similar temps in our basement, right now it is 73 (highest) and in the winter it gets around 55. My next venture will be to probably get a wood heater placed in basement with large vent hood over heater and insulated duct running to return side of air handler so I can just run my fan and heat the basement and entire first floor. We have a second floor but since we are empty nesters, we just use it as a heat sink, upstairs doors open in the summer and closed in the winter. Tickhill
"You will find the key to success under the alarm Glock"  Ben Franklin
Forget it Ben, just remember, the check comes at the first of the month and it's not your fault, your a victim.

Pray while there is still time

Dave Sparks

My advice based on offgrid mentality is to go mini split. You gain the lack of ducting which can be a 30% loss. The Seers are usually better and the Sanyo/Panasonics are absolutley amazing in their performance.
"we go where the power lines don't"

Native_NM

Mini split is a great option for cooling targeted areas. If you add the heat strip option it gets expensive in a hurry.  Every system I have seen is electric.  Gas is much cheaper in most areas.  There are pros and cons depending on each circumstance and needs. 

New Mexico.  Better than regular Mexico.


MushCreek

From my reading, I find the mini-splits are efficient down to surprisingly low temperatures; lower than I would experience in SC. I also have an endless supply of firewood (provided I'm willing and able to harvest it) so I'll probably supplement in the winter with wood. Seems like mini-splits may be the way to go.
Jay

I'm not poor- I'm financially underpowered.

Dave Sparks

Quote from: Native_NM on July 07, 2011, 10:56:13 AM
Mini split is a great option for cooling targeted areas. If you add the heat strip option it gets expensive in a hurry.  Every system I have seen is electric.  Gas is much cheaper in most areas.  There are pros and cons depending on each circumstance and needs. 



This is sort of incorrect! While there may be mini splits with an electric heat strip, the type I am refering to is a heat pump mini split. The cooling cycle is reversed and there is a gain in efficiency over an electric heat strip in a heating mode.
"we go where the power lines don't"

MushCreek

The type I read about are heat pumps, and are 100% efficient down into the single digits. There must be a different technology, because our heat pump here in FL is only good down to about 40. There are also multi-head mini's that can be set for different zones. One compressor, multiple cooling units.

I found out that natural gas is not available, so the only other gas option would be propane. We'll likely be all-electric, with a wood back-up for heat, and a generator during outages. I have a nice-size Honda genny for the ice storms.
Jay

I'm not poor- I'm financially underpowered.

Dave Sparks

Jay,

I have never seen anything that is 100% efficient other than the suns ability to bring everything back to a dust state over time.
The Sanyo's that I  and some of my clients use work well in the single digits for temperature. The refrigerant is R410A and that is the real advantage. The next refrigerant will be Butane and it will even be better. The Janpanese are already using it.
http://us.sanyo.com/HVAC/HVAC-Solar-Integration-Offgrid-Solar

The link above is some of the fruit from my work with Sanyo, now Panasonic owned.
"we go where the power lines don't"


MushCreek

I misspoke when I said 'efficient'. The term is 100% of it's rated capacity. The Mitsubishi is at 100% down to 5 degrees F., and still functional down to -13F. Daikin and Fujitsu make similar units. I haven't checked Samsung yet. They're not cheap when you get into multi-head units- about $5- $6K for a system big enough for a small house with 3-4 zones.
Jay

I'm not poor- I'm financially underpowered.

Native_NM

Quote from: Dave Sparks on July 09, 2011, 12:13:28 PM
This is sort of incorrect! While there may be mini splits with an electric heat strip, the type I am refering to is a heat pump mini split. The cooling cycle is reversed and there is a gain in efficiency over an electric heat strip in a heating mode.

You are sorta (ok, mostly) correct.  I was looking at a reference that compared the electric heat strips as opposed to heat pumps.  Looking at another site, mini-split can be more expensive in certain applications from an equipment standpoint because of multiple compressors, etc.

Some layouts are not really conducive to mini-split also.  Retrofit applications are easier. 

Depending on the layout, in new construction it might be cheaper over the long-term to install a traditional HVAC system. 
New Mexico.  Better than regular Mexico.

Dave Sparks

I am doing a pretty nice little solar home down in "better than Mexico" right now. Your comment that it might be cheaper to go with a ducted system might be true in average America in new construction.

In a Passive solar home there is huge cost in construction.  What I am finding, is that if there is a year round solar resource, like N. Mex, the cost of a good electric heat pump is many times cheaper, easier, better, and faster than building passive. Passive homes have their problems! It is a game changer for those with PV! It allows good construction techniques but does not require the complications that many passive home deal with.

It use to be that pumping water long hours was the main reason to solar track the sun. Running a heat pump on a tracker is just as valid.
"we go where the power lines don't"