Consulting-Specifying Engineer - April 2008 - (Page 46) IsRADIANTa n o p t i o n ? Radiant cooling systems may reduce energy consumption while decreasing cost. BY GEOFF MCDONELL, PENG., LEED AP, Senior Mechanical Engineer, Omicron, Vancouver, British Columbia. COOLING ention radiant cooling to most HVAC engineers and you get a funny look. The first thing they ask is “What about the condensation?” There seems to be an assumption that conventional 42 to 44 F chilled water supply temperatures are used for all cooling applications. In this case, if you used that kind of entering chilled water temperature for radiant panels, they will condense. Chilled water can still provide sensible comfort cooling even at elevated temperatures above 60 F; depending on the cooling terminal system, the ability to provide latent cooling is diminished. You also can get the benefit of higher chiller equipment energy efficiencies when the chiller, or chilled water plant device, operates at higher chilled water temperatures. M This photo shows the installation of radiant slab heating cooling piping along with cast-inplace displacement ventilation ductwork within a 10-in.-thick flat slab at the new City of North Vancouver Library, North Vancouver, British Columbia. This building features a highperformance exterior window system incorporating exterior shades and a fritting pattern on high-level “daylighting window panels.” This reduces the building heating and cooling loads down to the point where the radiant slab ceiling can operate above ambient dewpoint levels to provide effective radiant cooling with an average ceiling surface temperature of 63 F. The cast-in-place air-supply ducts serve in-floor air grilles to provide low-level displacement ventilation with the air being tempered to be supplied at nearly the same temperature as the slab for a “constant temperature building” HVAC system. Local room occupancy controls provide both airflow modulation and reheat/recool coils to provide additional local zone temperature control and “demand ventilation” for indoor environmental quality control. This particular building also uses a geo-exchange water to water heat pump plant to generate the moderate-temperature cool water used for cooling the slab as well as for the ventilation air tempering. Heat recovery dedicated outdoor air handlers equipped with heat recovery sections are installed on the roof to supply 100% fresh air throughout the building. Photo: Geoff McDonell 46 Consulting-Specifying Engineer • APRIL 2008
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