Hydronic cooling and De-humidification

[robertc65]

I have been reading up on Hydronic cooling and it sounds real promising. It seems that in areas of higher humidity some level of de-humidification may be required. Does anyone know if the Baltimore, Maryland area would require additional humidification when using Hydronic cooling.

Thanks

Rob

[teddy bear]

All green grass climates require supplemental dehumidification to maintain <50%RH during low/no cooling load with conventional a/c. A good iaq design includes 50-75 cfm of fresh make-up air natural or mechanical when occupied. This represents additional dehumidification load. Figure roughly 10 gallons/90pint/90,000 btus of latent load with a 70^F outdoor dew point.
Hydronic cooling is all sensible cooling. Therefore you need a 90 pint per day dehumidifier. Suggest a ventilating dehumidifier like Ultra-Aire as the ideal high efficiency device. Inaddition air filtering, air blending, and occupancy ventilation is included. Dehu TB

[pstu]

Just for education, I would like to see a discussion of how they make sure the cooling element does not get below interior dewpoint. Maybe I am seeing it wrong but it sure does seem like a remote possibility of a workable system. Just a concern from a homeowner in a definitely green grass climate.

As far as your recommendation of a dehumidifier to lower dewpoint, that seems such an obvious solution I wonder if there is any other way. I love my Thermastor, even though I don't *need* 42&#37; RH in the summer it's sure pleasant to have when outdoor dewpoint is 75.

Best wishes -- Pstu

[Shophound]

Just for education, I would like to see a discussion of how they make sure the cooling element does not get below interior dewpoint. Maybe I am seeing it wrong but it sure does seem like a remote possibility of a workable system. Just a concern from a homeowner in a definitely green grass climate.



Wouldn't be too hard to do. Have a temperature sensor and a humidity sensor in the conditioned space, sending data back to a controller that can calculate dew point from those two readings. The temperature sensor wouled be embedded in the material that is being hydronically cooled, such as a wall, floor, or ceiling section. The humidity sensor would read room air humidity. The controller would calculate dew point, and then reset chilled water flow through the cooling panels to ensure the surface temperature of these sections never falls below the dew point of the room.

At any rate, you would not want to run these surfaces very cold. The human body rejects heat via the three methods of heat transfer; convection, conduction, and radiation. With hydronic cooling surfaces, radiant heat loss would be the primary factor. If, let's say, a wall is being cooled hydronically, it should not be so cold as to make the occupants of the room feel chilly. The room air temperature could be 75, but if the wall was at, say 60 degrees, the occupants would probably complain of being too cold in that room.

I have not studied the subject deeply....these are just my thoughts looking at it from a design/operation perspective. Personally I think if such a system could take advantage of the thermal mass of a structure, such as slab foundations, masonry walls, etc., home comfort would become a matter of modulating building surface temperatures via hydronic cooling, and a whole house dehumidifier to control humidity. The latter could be easily combined with IAQ equipment, since it is not serving the double duty of dehumidification and comfort cooling.

[robertc65]

Thanks for the responses. In my case I have existing ductwork which is not large enough to supply enough air to the upper floors. Could I utilize this ductwork for the ventilating dehumidification?

Thanks

Rob

[firecontrol]

http://www.aprilaire.com/index.php?znfAction=ProductDetails&category=17&item=1700

This unit is a ducted whole house dehumidifier that could possibly use your existing ductwork.

[coolguysfl]

The Aprilaire living control center actually cycles the Aprilaire dehumidifier on dew point rather than RH.

The Honeywell 9000 (my personal favorite) will control the AC for partial dehumidification with a 3 degree over-cool OR allow total control of the RH via a humidifier + dehumidifier if stand alone products are installed. Considering hydronic cooling nets poor dehumidification this is your best bet.

[beenthere]

I guess its just me.

But, TB, is one of the PRO members that I would like to see more eucational posting from in the ED/TRAING from.

Can the Educational Comitee talk to him about this.

Thank You.

[cem-bsee]

get an outdoor RH% & temp unit & hang in shade 5ft from house & read yourself --
or
check NOAA.gov database

[Shophound]

I guess its just me.

But, TB, is one of the PRO members that I would like to see more eucational posting from in the ED/TRAING from.

Can the Educational Comitee talk to him about this.

Thank You.

I got your email yesterday, and I plan to forward your idea to my colleagues on the committee.

Thanks for the suggestion! :cool:

[teddy bear]

The Aprilaire living control center actually cycles the Aprilaire dehumidifier on dew point rather than RH.
bet.

Controlling the dehu with dew point controller over runs the dehu. Materials and mold/dust mites respond to the %RH. Ideally 50%RH is midrange. A/c on/off is a 15^F range, 70^F-85^F. Maintaining 50%RH is from 55^F --64^F dew point across the temp range. This advantagous during when the space is unoccupied and no cooling needed. Over running the Ap dehu is common. %RH works well. %HR can be added to Ap dehu. High efficiency dehus add less heat to the space than conventional dehus. Dehu TB

[beenthere]

Thanks for the suggestion! :cool:


No problem.

[gmcd]

In Europe, where radiant cooling is pretty well established, the sheets of capillary tube radiant mats that they use come with a small dewpoint sensor built right, in to reset the cooling water supply up a degree or two as required if the indoor humidity rises above the setpoint. It's also easy to incorporate dewpoint sensors on a couple pieces of bare cooling water pipe to sense if you have issues. Finally, even if you get transient conditions where the indoor humidity and dewpoint gets above your radiant cooling system operating temperature, you won't have indoor rain at all. Check out these links for information, and especially Dr. Mumma's paper on his tests to create condensation on radiant cooling panels- took 8 hours at 14F below the dewpoint to get visible drops.

http://doas-radiant.psu.edu/IAQ3.pdf

http://doas.psu.edu/papers.html

http://doas-radiant.psu.edu/Journal2.pdf

http://www.radiantcooling.org/capillary.htm

Or just do some Google searching on "radiant cooling" and spend the next few days reading and absorbing. There are lots of radiant cooling systems operating now in North America, it's just a matter of getting over the "all-air" mentality and the myths to be able to design and apply it properly