A/C for radiant house

Cliff Brady

ChrisL

A/C Spacepak or Conventional for low humidity

I've changed the heat over in my house from forced air to radiant floor/panel. The existing ductwork for the 2nd floor is not acceptable for cooling. (no returns on 2nd floor, floor mounted vents.

I have full attic access to run ductwork for 2nd floor. I am leaning towards a conventional system, but really appreciate the low humidity that the spacepak offers. Is there any way to get this from a conventional system without running low room air temps. I realize a variable speed air handler can work ok, but the lower fan speeds to achieve lower humidity might not work too well in distributing the air satisfactorily in a high cathedral ceiling bedroom.

Thanks,

ChrisL

Brad White_60

Low RH

The only practical way to reduce humidity with any AC system is to depress the temperature below the dewpoint of the target space. Typically this is 55 degrees F or lower, a "traditional" supply temperature.

(55 degrees corresponds with the dewpoint of a room at 75 degrees and about 50% RH in case you ever wondered.)

The SpacePak/Unico High V systems dehumidify so well because, as you probably well know, they cool the air to the low 40's high 30's sometimes. That is dry when it gets to the space.

With a conventional system you have some options but they will require some work.

Many conventional systems have a dehumidification mode whereby the fan slows down and the DX process continues, ignoring any cooling demand.

Less air at a colder temperature is the principle, and longer retention time across the coil helps this along. That alone may work for you. If your loads are such that humidity control is more critical, here are some other ideas/concepts:

One is to effect a "face and bypass" arrangement such that much of the air goes across the evaporator (cooling coil) and the rest around it (bypassed) to mix before being supplied to the space. Thus the air that goes through the coil comes out colder (target 42-45 degrees) with less absolute humidity. The bypassed air brings the temperature back up. Naturally you have to watch your refrigerant side when you do this so you do not freeze up your coil.

On larger systems this can be automatic with a modulating linked damper. Dual-Duct and Multi-Zone systems fall into this category, but smaller systems tend to favor simple manual fix and forget dampers.

The other way is called "reheat". After cooling the air below dewpoint, -presumably too cold and would over-cool the space-, you have to add heat before supplying it. A second coil is installed downstream of the main evaporator. This often runs just on space temperature. This can be an Energy Hog and most energy codes prohibit or restrict it's use.

The least energy-cost way to reheat is to use hot gas from the refrigerant process. This is commonly done in dehumidifiers, particularly pool dehumidifiers.

If not refrigerant, then hot water is the obvious choice. But you will pay the price in double energy, once to cool, again to heat.

In some larger commercial systems I use condenser water as a form of "free" (low cost) reheat energy because it is waste heat. Or use drycoolers to the outside and run warm-ish water to the reheat coil. All you need to add is enough to take up the difference between system output and room load. Any heat gain in the space is the same as reheat.

Start with standard manufacturer's offerings and adapt from there.

My $0.02

Brad

Mike T., Swampeast MO

Check out the Rawal APR Control.

I've yet to use one but plan to fairly soon. Finally heard from one actual user and the device works as claimed. Especially effective at removing humidity without overly cooling the air.

Kniggit_3

Goodman/Amana Variable have a dehumidificaton tap on the Variable speed control to lower the speed, and hold it there untill the air dry, while still operating on the thermostat. now on a really sweet system combine that with a 2 stage system and you have the most even comfort available. I have one of the Aman RSG condensers operating here and its quiet as a church mouse, and has kept the house nice and dry. I beleive that a properly installed Variable two stage system will perform better then any Space-Pack High velocity system, Easy.

Cliff Brady

Heat Pipe passive dehumidification

Heat pipes may be described as having two sections: precool and reheat. The first section is located in the incoming air stream. When warm air passes over the heat pipes, the refrigerant vaporizes, carrying heat to the second section of heat pipes, placed downstream. Because some heat has been removed from the air before encountering the evaporator coil, the incoming air stream section is called the precool heat pipe.

Air passing through the evaporator coil is assisted to a lower temperature, resulting in greater condensate removal. The "overcooled" air is then reheated to a comfortable temperature by the reheat heat pipe section, using the heat transferred from the precool heat pipe.

This entire process of precool and reheat is accomplished with no additional energy use. The result is an air conditioning system with the ability to remove 50 to 100% more moisture than regular systems.

Please email me if you would like more information or pricing.

Cliff

http://www.heatpipe.com/heatpipes.htm
http://www.heatpipe.com/mktg_materials/Brochures/zcoil.gif
http://www.heatpipe.com/mktg_materials/Brochures/Residential Line.htm
http://www.heatpipe.com/mktg_materials/Brochures/hpcases.pdf

John Mills_5

Variable Speed

As previously mentioned with Amana, but it applies to all brands, the variable speed air handlers let you slow the blower in periods of high humidity. There are several stats out there with this capability built in. So instead of using HV which kills SEER and capacity, you can use a variable speed conventional blower which BOOSTS SEER and still have extra humidity control.