The New HVAC Frontier: Radiant Cooling and Chilled Beams
Radiant cooling and chilled beams are the latest advancement in hydronics, and we at Taco want to start a conversation about the technology behind radiant cooling and chilled beams and the broad applications for its use in today’s commercial and institutional buildings. In doing so, we’d like to find out what you think about this development, so we encourage you to weigh in.
A popular indoor cooling option in Europe, we believe that radiant cooling using passive/active chilled beams is going to become just as widespread an application here in the U.S., as engineers and building owners come to understand its advantages over a forced air, DX-type cooling system.
Not to be left out of this marketplace, Taco has developed a new product application for radiant cooling and chilled beams that we’re quite excited about. It involves low flow injection pumping that can make radiant cooling and chilled beam systems even more efficient. More on that as we go along, but first, let’s start by briefly describing the technology behind European radiant cooling systems during the past several decades.
Commercial radiant cooling HVAC systems originated in Europe during the 1980s as the need for sensible cooling of commercial buildings rose in response to the use of
personal computers. To satisfy the need for indoor cooling, Europeans developed radiant chilled ceilings. These consisted of metal panels with hydronic tubing attached to circulate chilled water. Using small pipes instead of large ducts was an advantage due to limited ceiling space. Today’s chilled panels can now use plastic pipes embedded in ceilings, walls or even floors.
Approximately 50-60 percent of the heat transfer from a radiant chilled panel is radiant, while 40-50 percent is convective. Chilled water temperature must be above the dew point – between 55º and 60ºF – to prevent condensation from forming on the bottom of the panels and “raining” down from the ceiling. Therefore, the driving force or approach between the chilled water and a room space is reduced to 15º to 20ºF. This is approximately half of a conventional chilled water system, where 40º to 45ºF chilled water produces an approach of 30º to 35ºF.
As a result, a radiant chilled ceiling requires higher chilled water flow rates to achieve reasonable capacities – approximately double those of conventional chilled water systems. Even with higher flow rates, however, radiant chilled panels and ceilings have relatively low capacities, ranging from 20 to 40 Btuh per square foot of panel area.
Because the chilled water temperature supplied to a radiant chilled panel ceiling is above the dew point, radiant chilled panels cannot provide latent cooling (dehumidification) capacity. To supply that capacity, a separate, 100 percent dedicated outdoor air (DOAS) unit is used for latent cooling, and works by slightly pressurizing the building with dry treated outdoor air from the DOAS unit to prevent the infiltration of warm, moist outside air. This addition of the DOAS allows the combination decoupled system to provide both sensible and latent capacity.
The biggest advantage of decoupling sensible and latent loads is substantial airflow reduction, lessening the needed air changes per hour (ACH) down to 1 to 2 changes. A typical air-based cooling system would require 7 to 10 ACH of recirculated and outside air. This substantially reduces the horsepower and materials required to move cooling energy around the building.
Up next time: The evolution of chilled beams.
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