When you think of a hydronic system, you probably think of water or steam being used to heat an application. Hydronic heating — particularly the in-floor radiant system — is a popular option for many residential applications, because of the more constant, even temperatures a properly designed system can maintain.
But cooling is a different story. Contractors who install hydronic systems often leave the cooling to their air-side partners. These contractors usually rely on conventional air conditioning systems or possibly a high-velocity ducted system to cool a space that utilizes hydronic heating. Paying for a second system is not a palatable option for many homeowners, though, who have already shelled out a premium price for a hydronic system.
There are some, however, who say that hydronic cooling can be useful in certain residential situations. It’s important to note that there are design considerations that must be observed to produce cost-effective hydronic cooling; however, it’s worth taking a look at all the options.
Where it Works, Where it Doesn’t
David Springer, president, Davis Energy Group, Davis, CA, notes that his company, which is a mechanical engineering firm specializing in energy-efficient heating and cooling of buildings, has completed commercial projects that prove hydronic floor cooling can significantly reduce the size of the cooling system by shifting loads, as well as saving on initial equipment cost and demand charges.In a residential application, Springer says that the best opportunity for hydronic cooling is in two-story residences. “The best application is to radiantly cool the first floor (using extensive ceramic tile) and use the same chilled water to provide forced air cooling from a second-floor air handler. Unless the climate is dry, and the owner is satisfied with tile floors almost exclusively, hydronic cooling doesn’t make sense for one-story homes.”
A chilled water source is obviously necessary if cool water is to be circulated throughout a home. There isn’t any “one-size-fits-all” source that works best for every application.
John Howell, executive director of The Hydronic Foundation, Johnson City, TN, says that for a small household in the southeast part of the country, the heat pump would probably work best. “This has brought the luxury of affordable cooling into the life of the ordinary household,” he says. But he also notes that in this part of the country, tight construction and high humidity are important issues.
For upscale residences, dormitories, nursing homes, or light commercial applications, Howell says that the valance system is a great choice. “It provides room-by-room temperature control and offers quiet, clean, unobtrusive, and economical distribution of energy. For other applications, fan- coils can provide makeup air as well as cooling.”
In the Southwest, where humidity is low, another option might be an evaporative cooler, which can be connected directly to the hydronic system.
Springer notes that there are a limited number of air-cooled chillers for residential and small commercial applications. He says that an inexpensive residential air conditioner can be converted to a chiller by the addition of a heat exchanger; however, it may be difficult to find the right kind of heat exchanger. “There is a need for a manufacturer to produce a low-cost, compact, efficient refrigerant-to-water heat exchanger that includes the expansion device and protective controls that can be readily coupled to 2- to 5-ton condensing units,” says Springer.
Howell points out that air-cooled hydronic chillers and heat pumps are available in his area, including split systems with condensing units from 3 to 5 tons and support wall- or floor-mounted chillers up to 15 tons. “Direct air-cooled chillers range from 1 to 12 tons, and these chiller systems come complete with capacity reduction controls, pump, and expansion tank,” says Howell.
Watch Out for condensation
Once a chilled water source is established, it is necessary to determine how to distribute that cool water throughout the home. The biggest enemy of hydronic cooling is condensation. Howell says that contractors need to be aware that chilled water tubing must be insulated to minimize condensation. “There will be condensation from heat exchangers, such as fancoils or valance units, which must be drained. To minimize piping costs, use a two-pipe system. The same piping, if properly insulated, can be changed over manually or electrically to be used as supply and return for heating or cooling, depending on the season.”For the greatest flexibility, four-pipe systems are generally used, notes Howell. He also says that condensate drains, if piped to a sewer, must be trapped. “In many installations, a 3¼4-in. PVC tube is projected about 3 1/4-in. beyond the exterior wall, where the condensate can drop to the ground or dissipate in the air.”
If tubes are run through a concrete slab, Howell says that hydronic cooling won’t normally work, mainly because of the condensation problem. But another problem is simply the laws of physics, which cause cool air to fall to the lowest level.
Retrofitting a system can be difficult as well. If the tubing for radiant heating runs through the slab, you can’t retrofit it for a hydronic cooling system for the reasons stated above. The existing in-the-wall piping for hot water or steam may not be insulated, and that is necessary to minimize condensation. Finally, the heating-only fancoils or convectors may not be suitable for chilled water operation because of location or lack of a condensate drain.
Other than that, retrofits should be fairly simple, says Howell. “It’s relatively easy to retrofit a valance-mounted system. The existing hydronic heating system can remain or the existing heat exchangers, radiators, or baseboards can be removed, and the old piping can be abandoned in place. New insulated piping or tubing can be surface mounted on the walls, tested and inspected, and then covered with UL-approved plastic chases, which can be painted so they become part of the décor.”
Overcoming the expense may be another hurdle for hydronic cooling. Good design is the key to keeping costs in bounds. Economy is achieved by installing hydronic cooling and heating at the same time and using the same heat exchangers for both functions.
Howell says that the key to overcoming the expense objection is to educate your customers about the added benefits of a complete hydronic comfort system.
“If a customer is willing to pay for a well-built residence, then it’s folly not to include an integrated hydronic system including a single heat bank for space heating, snow melting, pool warming, and domestic hot water; a single chiller bank to provide chilled water; a passive distribution system, such as the valance; and a makeup air system to provide adequate airflow at 50% relative humidity for the design occupancy.
“The customer isn’t paying extra, he’s paying for amenities, quality, and low operating costs — the same sort of things he sought when he bought his automobile.”
Hmm…good point. Makes you want to take a look at hydronic cooling, doesn’t it?
For more information on hydronic cooling applications, check out The Hydronic Foundation’s website at www.hydronics.org.
Publication date: 10/02/2000
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