Radiant Cooling – Part 1
Most heating professions are very familiar with the principals of radiant floor heating systems and how they work. These systems have become an accepted part of the HVAC offering of many engineers and contractors, as they have proven to offer customers comfortable, efficient, healthy and quiet heating systems. Ask many of those same engineers and contractors about radiant cooling systems and you will probably get a mix of confusion, fear of the unknown and dismissal.
Cooling with radiant however, offers many of the same benefits as radiant heating; cooling systems that are comfortable, efficient and quiet. Radiant cooling systems have been widely used in Europe for some time and they are starting to become more popular in North America, especially in the dry climates of Southwest USA. According to Jerry Leyte, Central Canada sales manager for Uponor, there are now quite a few radiant cooling systems installed in Canada
“There are radiant cooling systems installed in the Calgary and Winnipeg Airports, as well as the Toronto District School Board and Manitoba Hydro Place office that are performing exceptionally well,” notes Leyte. “Most applications for radiant cooling are in commercial applications such as airports, offices, schools, and large public areas such as museums. Residential applications are not very common, but can be installed if they are very carefully controlled,” adds Leyte.
Radiant cooling follows the same principles as radiant heating, but in reverse. Thermal energy is exchanged by radiant heat transfer between the heat loads present in the space and the cool floor or ceiling. Energy radiates from the objects, people, equipment and lights to the cool surface, which is opposite to what happens in heating mode, where the heated panel radiates to the objects and people. It is possible to have radiant panels that provide both heating and cooling, providing the best comfort and efficiency all year long.
There are two broad types of radiant cooling systems, which are chilled slabs and radiant panels. Chilled slabs offer benefits of integration into the building, lower installed cost and increased thermal mass. Often referred to as thermally activated building systems (TABS), this large thermal mass can be advantageous for some applications, where the mass can be “charged up” during times of off-peak electrical rates. Radiant slabs can be arranged so that they are exposed on both sides, providing, at different times of the year, radiant heat to the space above and radiant cooling to the space below.
Radiant cooling slabs use similar design and sizing principles as a hydronic radiant floor system, using the same types of PEX pipes, manifolds and pumps as in heating. Chilled water between 55F to 58F is circulated through the pipes, which are embedded in either floor or ceiling. Radiant cooling slabs require a close tube spacing of six to nine inches on centre, which is a little tighter than the nine to 12-in. normally required for radiant heating.
Radiant cooling can also be delivered through specialized panels, which would typically be attached to ceilings, but can also be attached to walls. Panels offer installation flexibility in terms of where they can be placed and how they are integrated with dropped ceilings, lights and other electrical systems. The lower thermal mass of panels allows them to react very rapidly to changing loads. Radiant cooling panels are designed so that they can be retrofitted into the ceilings of older buildings as the plenum space requirement is minimal relative to fan coil units or VAV systems.
Radiant cooling from a slab can be delivered to a space from the floor or ceiling. Since radiant heating systems tend to be in the floor, the obvious choice would be to use the same piping for circulating cooled water. While this makes sense in some cases, delivering cooling from the ceiling has several advantages. It is easier to leave a ceiling exposed to the room below, which creates a better radiating surface to occupants and objects. As floors will often have coverings and furnishings, the effectiveness of the radiant cooling effect through the floor can be decreased. The ceiling will also come in contact with any rising warm air, creating greater convective heat exchange and a better cooling effect. Cooling delivered through the floor does make more sense when there is a high amount of solar gain directly onto the floor, because the cool floor can more easily remove those loads than the ceiling.
Part 2 ...............
Original Article: HPAC Magazine: https://www.hpacmag.com/features/radiant-cooling/
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