ACHRNEWS

Couple mini-duct systems with radiant floor heat

April 26, 2000
A boom in high-end custom home construction, coupled with constant advances in home technology, have led to a demand from consumers for more-than-traditional heating and air conditioning systems.

Today’s homeowners are looking for a total comfort solution, a simple way to keep their homes at an ideal temperature, no matter the season. The task seems anything but simple — maintain a comfortable temperature in every room of a home on frigid winter nights as well as scorching summer days without cluttering up a home’s aesthetics or charging homeowners their life savings.

But it is possible, and an efficient, effective way to do it involves pairing a radiant floor-heating system with a mini-duct, high-velocity, central heating-cooling system.

Floor heating

One solution to home heating is a radiant floor system. These systems run heated water or glycol through flexible plastic tubing, about 1/2- to 1-in. dia.

The tubes are typically laid out in a coil pattern and evenly distributed throughout the subfloor. Tile, hardwood, or carpeting is laid over this subfloor and the tubing acts as a massive radiator, heating a home from the ground up.

The benefits of heating with radiant floor systems include efficiency and aesthetic value. Instead of metal registers blowing hot air as with traditional systems, creating hot spots in some areas and drafts in others, radiant floor systems spread warmth throughout an entire home.

Because the radiant system warms the objects in the room, not the air, the room quickly regains its temperature when the door to the outdoors is closed. Radiant floor heat can be controlled from room to room, so a seldom-used guest room can be kept at a lower temperature than the family room or kitchen.

Heating with a radiant floor system is also energy efficient, as the water only needs to be heated to 90° to 130°F to heat the home, producing comfortable temperatures at lower thermostat settings and reducing heating costs.

Mini-duct cooling, heating

Although radiant systems provide a comfortable home environment throughout the winter months, the systems offer no solution to the problem of effectively cooling a home. Therefore, a separate cooling system is needed, the most efficient of which to pair with radiant floor heat for overall comfort is a mini-duct, high-velocity system.

A mini-duct system delivers conditioned air to rooms via flexible, 2-in.-dia. supply tubing that fits into spaces that won’t accommodate conventional sheet metal ducting. The tubing terminates in small, unobtrusive outlets in the walls, floors, and ceilings. In addition to the difference in supply ducting, the method of cooling with a mini-duct system is quite different.

Conventional systems consist of a cooling element, such as a metal coil, and a fan, which blows air over the coil and pushes it into the room through metal ductwork.

Mini-duct systems can provide cooling through one of three methods: by using a traditional DX coil with a refrigerant, a heat pump coil in cooling mode, or a chilled-water coil. Air is drawn across the coil with a mini-duct system as opposed to pushed as with a conventional system.

The advantage to this method is that it actually takes longer to move the air across the coil and, because most mini-duct systems also use coils with a greater surface area, this actually makes the air colder and can remove as much as 30% more humidity from the air than conventional systems. This means that you can be comfortable at higher thermostat settings, increasing efficiency and reducing cooling costs.

Mini-duct systems can often heat in the same way as they cool, using a heat pump coil in temperate regions or using a hot water coil that acts as a radiator. As in the cooling mode, air is drawn across the coil and is heated to a higher temperature — providing hotter air to the room at lower thermostat settings.

A mini-duct cooling and heating system allows for flexibility in installation. The system’s air handlers and flexible ducts fit into tight spaces, so there is no need to drop ceilings or build soffits or other hiding places to conceal metal ductwork runs.

Mini-duct systems work on the principle of aspiration to provide even temperatures throughout a home. Whereas traditional central hvac systems diffuse air, a mini-duct system provides hot and cold streams of air that are moved through the compact tubing at a higher velocity, creating gentle circulation without drafts, so that “even” room temperatures can be enjoyed from floor to ceiling.

The rush of air cannot be felt more than a few inches beyond the outlet. A mini-duct system in cooling mode also removes up to 30% more moisture than conventional systems because its unique coils are colder than conventional coils, which is especially beneficial in areas with high humidity.

How they work together

Radiant floor and mini-duct systems have several of the same advantages. Installing them together in a home enables the two systems to complement each other, providing maximum indoor comfort.

Both provide a high degree of air quality and eliminate the loss of conditioned air typically experienced with forced-air systems. The mini-duct system can further increase indoor air quality when coupled with an air purifying system.

Radiant floor heating is often installed in the “cocoon” of the house, or the most-often-used rooms, on the first floor (i.e., kitchen, living room, and bathroom).

The mini-duct air conditioning system is used as the primary cooling source for all floors of the house. Complementing a radiant system, a mini-duct system with a hot water coil is used for heating the second, third, and higher floors. The home’s boiler supplies hot water for the heating coil.

The mini-duct system allows a room to be quite comfortable at a low water temperature, which is more energy efficient. In addition, heating this way cuts down on the constant recycling of the boiler and hvac system.