Comfort Is More Than Heat

Cooling, ventilation and dehumidification in a radiant system.

When it comes to comfort, radiant floor heating is clearly the heating system of choice. But comfort isn’t limited solely to warmth. For a climate-altering system to fully provide true comfort, it should also address air quality (via proper ventilation), and in most climates, cooling and dehumidification as well.

Think of a home in ecological terms. The home is a microclimate that the inhabitants depend on for their comfort and health. “Comfort ecology” could be described as the relationship between the inhabitants of a home and all the factors that create and maintain their comfort.

The human body is an incredibly sophisticated instrument when it comes to sensing comfort. Our entire body is covered with receptors that allow us to sense from our environment variations in heat, cold, air movement and humidity. The fact that our bodies sense or discriminate more comfort when in the presence of radiant heat than when exposed to traditional drafty mechanical systems largely accounts for the phenomenal growth in the use of radiant floor heating.

With any heating system, our bodies sense comfort over a wide area and from many factors: from air temperature, air movement (wind chill) and, perhaps most of all, from temperatures radiated by the surfaces in a room. Radiant heating evenly and silently distributes comfort over wide areas and makes large surface areas warm, which is ideally paired with how our bodies sense comfort.

By the same token, the goal of properly designed cooling, dehumidification and ventilation systems is to provide that same effective, even distribution of comfort.

Increasingly, radiant heating contractors are thinking of themselves in broader terms, as contractors of comfort. A true “comfort contractor” will address heating ventilation, dehumidification and cooling in an overall design in which all these components work together.

According to Larry Drake, executive director of the Radiant Panel Association, the single most commonly asked question in relation to radiant floor heat is, “Can I cool also with my floors by pumping chilled water through them?”

His answer: “It depends on humidity, climate and control. Yes, it can be effectively done, but there are issues that must be resolved.”

Since warm air will hold more moisture than cold air, if a floor is cooler than the ambient room temperature, that moisture will condense onto the floors, unless you install a proper simultaneously operating dehumidification system.

“Arid desert climates require less dehumidification, which makes the use of radiant floors for cooling easier,” Drake explains. “However, often more cooling is needed than the floor can provide, in which case it’s more economical to have a separate heating and cooling system.”

A separate heating and cooling system is the usual solution. But from a comfort point of view, where expense is not an issue, Drake stresses that “the ultimate system is radiant floor heating.” And for cooling: radiant cooling with floors, plus an efficient air dehumidification system, augmented with a little extra cooling capacity on the air side.

The first option is a home design that minimizes your cooling requirements. Roof overhangs and glass placement in particular can have a huge effect on how much cooling your home requires.

Cooling your radiantly heated home offers all the normal home cooling choices, but with some additional possibilities provided by hydronics. Cooling with floors, as described above, is a possibility if dehumidification is properly addressed. Many hydronic contractors have been drawn to cooling with chilled water systems, since they can use it in many ways. As with hydronic radiant heating, chilled water systems offer the benefits of small, easily insulated pipes, and the ability to pump chilled water (without architecturally intrusive ducts) to the location where the cooling is most needed. At that location, large air handlers (using ducts) or small (point source) air handlers can distribute this into a room as cool air, or in some cases this circulated chilled water can additionally be used for radiant floor or ceiling cooling. These systems may be easily zoned for energy efficiency, offering cooling area-by-area as needed.

Among the many other often-used good options for adding cooling to the radiant heated home are: conventional ducted air conditioning, conventional air-source heat pumps, split systems, ground source heat pumps (water-to-water or water-to-air), and small duct high-velocity systems.

What works best is often dictated by your climate, by the structure and size of the project, and by the expertise of your contractor.

Air quality is a bigger issue now, with tighter, more energy-efficient houses. Outgassing from a variety of sources - the materials in a home, household cleaning chemicals, cooking, etc. - all add up to the fact that a healthy house needs healthy air exchange, whereby some of the heated air is replaced by fresh air from the outside. The use of green flooring goods will partially improve the air quality of your home, but it won’t eliminate the need for ventilation.

The most energy-efficient way to accomplish ventilation is through the use of heat recovery ventilators (HRV) or energy recovery ventilators (ERV). These units recover heat from outgoing air and transfer it to the incoming air. The core in an HRV transfers heat from one air stream to another, whereas ERVs typically transfer moisture as well. The choice of which to use is usually dictated by climate.

In the cold climates of North America, HRVs are most frequently used, since in the wintertime, air inside the home often becomes more humid than the cold outside air, and it helps to exhaust some of the humidity.

In very mild climates, it is possible to use exhaust-only ventilation, with small air intakes distributed throughout the house.

A modest amount of continual air replacement is desirable, and this can be accomplished using small fans with whichever system you choose. Several brands of air handlers have HRVs built into them; these can operate at a slow speed when in the ventilation mode, and at higher speeds when there is, for example, a requirement for cooling. During the heating season, they may quietly operate at the low ventilation speed.

The versatility of radiant systems just keeps growing. The mechanical systems role in “comfort ecology” has moved way beyond warmth to also providing integrated healthy ventilation and cooling comfort.

Editor’s note: This is an edited version of an article appearing in the 2007 edition of the Radiant Flooring Guide. For more information about the guide, contact the RPA at 800/660-7187 or info@rpa-info.com.