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"...humidity management is necessarily required by the HVAC system for microbial control over pathogens (bacteria, viruses) and allergens (molds and dust mites); and to promote respiratory and thermal comfort for occupants; and for the dimensional stability in hygroscopic materials like wood. When managed for these priorities, condensation on radiant cooling panels becomes a moot point."

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Très Bien for large scale radiant cooling
Copyright Robert Bean, R.E.T., P.L.(Eng.), All world rights reserved. Originally published in HPAC Canada, Sept. 2012

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I have lost count of how many years I have been harassing industry and its various constituents to adopt radiant cooling for conditioning occupants and spaces. Even to this day naysayers argue against it spouting over condensation potentials. Few of these reluctant cynics ever consider that 100 per cent of all condensation problems in buildings conditioned exclusively with air did not have radiant cooling to blame so let’s stop blaming radiant panels for condensation problems.

This in fact was the message in my 2012 ASHRAE San Antonio and ACCA Rhode Island presentations where I and my learned colleagues demonstrated that humidity management is necessarily required by the HVAC system for microbial control over pathogens (bacteria, viruses) and allergens (molds and dust mites; and to promote respiratory and thermal comfort for occupants; and for the dimensional stability in hygroscopic materials like wood. When managed for these priorities, condensation on radiant cooling panels becomes a moot point. Do not get me wrong, I am not saying you do not need to monitor surface dew point temperatures and space humidity with radiant cooling systems. I am saying: get your design priorities in order and follow up with systems and controls that enhance the indoor climate for health of the environment and by association health of the occupants and for the dimensional stability of architectural materials. Do this and the condensation issue disappears.

To illustrate examples of what I am talking about, I have selected three large commercial projects, which represent a plethora of other buildings around the world. All of these follow a common HVAC recipe for success; that being a hybrid radiant-based comfort system using dedicated outdoor air for deodorization, decontamination and dehumidification of ventilation air. These buildings represent seasonal climates ranging from cold/dry to hot/humid; cold/dry to hot/dry and warm/hot and humid; and serve as examples of radiant cooling in high rise office towers, low rise office buildings and large scale transportation centres. In this they also demonstrate the ability to handle the variable flow of human traffic typical of the proverbial 9:00 a.m. to 5:00 p.m. employee or the seasoned air traveler.

What these diverse buildings in diverse climates initially have in common is an integrated design process with exhaustive planning around Indoor environmental quality and energy. No building discipline was excluded and energy models and simulations were done early in the concept phases to develop best practices and strategies. Since energy conservation was of upmost importance in these examples, comfort systems were based upon high temperatures for cooling and low temperatures for heating, both of which enable maximum efficiency from cooling and heating plants. By low temp/high temp we mean “tepid”...learn to forget the phrase, “hot water heating” or “chilled water cooling.” In the former we are talking radiating heating surfaces cooler than skin temperatures with fluids often cooler than blood temperature; and in the latter, cooling surface temperatures within 10
°F (6°C) of space temperatures using fluid temperatures similar to tap water.

As discussed in previous articles, the beauty of these buildings and their indoor climate systems is the separation between thermal comfort and indoor air quality, which models human physiology and reflects the individual ASHRAE standards addressing indoor environments (ASHRAE Standards 55, 62.1, 62.2). By removing the inherent conflicts with all air systems, each individual system of the hybrid actually enables the other to do its job without sacrificing performance for the other.

So let me now briefly introduce the three buildings and encourage you to do your own detailed discovery of these amazing buildings and their HVAC systems.

Suvarnabhumi International Airport (Bangkok, Thailand), Manitoba Hydro Place (Winnipeg, MB, Canada), and National Renewable Energy Laboratory (NREL) Research Support Facility (Denver, CO, USA) are three large projects (see Table 1), which successfully handle variable loads in diverse climates using the systems above. Each in its own way handles the external environmental conditions and variable occupant’s loads with a combination of architecture, interior design, lighting and radiant based HVAC systems. In the case of the Bangkok project we find a hot humid climate at summer design conditions of approximately 36
°C dry bulb/26°C wet bulb with an internal occupant load estimated at 12,025 people per hour. Next in line is Manitoba Hydro Place with an approximate summer condition of 35°C dry bulb/20°C wet bulb and an internal daily occupant load estimated at 1650 people, followed by the NREL Research facility with a summer climate condition of approximately 33°C dry bulb/15°C wet bulb and an internal daily occupant load estimated at 850 people. Notice the similar summer dry bulb temperatures but vastly different web- bulb temperatures.

Let me put the occupant effect into perspective. The metabolic rate of a seated airport traveler or office worker might be 350 Btuh spiking to 1000 Btuh for someone walking briskly to catch a plane. Of this combined load, one third to two thirds can be a latent load of about 105 Btuh (seated) or 625 Btuh (walking) or two thirds to one third being a sensible load of which the radiant cooling is very effective at absorbing. The latent load due to ventilation, infiltration and occupant load is effectively managed by delivering 100 per cent outdoor air, cool and lean enough to absorb the anticipated space moisture to a minimum 1
°C to 2°C (2°F to 3°F) wet bulb differential below the dew point of the cooling surface.

There you have it. It is thumbs up for large scale radiant cooling and you now have projects to explore at your own pace. This hybrid design process is the subject of upcoming courses (see in Vancouver, Toronto and Montreal so that you too can practice what skilled indoor climate engineers are doing here and abroad.


Radiant Cooling Project Bangkok
Figure 1. Suvarnabhumi International Airport (Bangkok, Thailand)
Radiant Cooling Project Manitoba Hydro
Figure 2. West side of Manitoba Hydro Place (Winnipeg, MB) showing solar chimney on the left.
Radiant Cooling Project NREL RSF
Figure 3. An air intake structure outside the west wing of the NREL Research Support Facility - nicknamed ''the football'' takes in chilly night air to cool the data centre. Such air-intake structures are key to lowering energy costs in the new building.
Radiant Cooling Project Overview
Table 1. Design summary.
For additional support visit our visitor services page.
Additional resources:
  1. How to use the ASHRAE Design Graph for Radiant Panels
  2. Radiant Cooling 
  3. ASHRAE San Antonio Seminars
  4. ACCA Radiant and Hydronics Council - Roundtable
  5. Sample radiant cooling calculation procedure.

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