Selecting radiant ceiling cooling and heating systems (part 2)

This three-part series provides an overview of the most commonly available and applied commercial building radiant cooling systems. Part 2 covers the most common commercial radiant cooling systems.

11/16/2007


Editor’s note: This three-part series provides an overview of the most commonly available and applied commercial building radiant cooling systems. There are also a wide variety of radiant “heating-only” devices that are available, such as low- and high-intensity fuel-fired infrared heaters and electric radiant heating panels and sheets, but the scope of this series is to examine active radiant cooling applications for commercial buildings.

PART 1 OF THIS ARTICLE: Read part 1 by clicking here .


The three most common radiant cooling systems used in many areas of the world are: suspended radiant ceiling panels, applied capillary tubes, and concrete core conditioning systems (radiant slabs). Residential wood frame buildings also may use commonly available radiant floor PEX tubing systems, applied as wall or ceiling systems instead of floor systems.

There are other examples of radiant cooling devices and systems, such as chilled beams, and combined chilled ceiling panels with integrated air supply terminals, but they are not widely available.

Suspended radiant ceiling panels

Suspended radiant ceiling panels have been available for the past few decades, and early attempts at using them for radiant cooling applications were less than acceptable, primarily due to trying to operate small panel areas at too cool a temperature for too high a cooling load, which resulted in condensation issues. The use of suspended radiant heating panels is well known and a common application for perimeter heating compensation systems.


These suspended radiant panels generally consist of copper or plastic tubing adhered to the back of an aluminum or steel panel, and suspended as part of a ceiling system over the occupied space. A mat of insulation is laid over the backs of the panels to “drive” the radiant energy down through the exposed face of the panel. These panels have a relatively light thermal mass and therefore respond quite quickly when a control valve is opened or closed to modulate the warm or cool water flow through them.

Typically they have a response time of about 15 to 20 minutes and can be controlled by standard HVAC controls for relatively fast-acting temperature control functions and short term transient loads in the space. Due to the rapid heat gain and response time of these systems, a chilled water source is required to provide sufficient cooling water at around 62 F during the daytime occupied periods.

Radiant ceiling panels may be economically feasible if they are used as “second stage” cooling and heating temperature control due to their ability to be controlled in discrete zones. This will provide a bit of energy efficiency at the end of the day, as well as keep the total area of the radiant panels to a minimum to keep costs down.

The greatest energy efficiency gains for a building are found by using high-performance glazing to reduce and eliminate the perimeter zones (high transient thermal loads) we’ve all become used to, and then use the radiant ceiling panels exclusively for all of the sensible space temperature control. This allows the air system to be reduced to a dedicated outdoor air system. The savings in the reductions of the mechanical HVAC system components would assist in offsetting the premium costs for the high performance glazing. The whole human comfort equation also can be addressed, resulting in very good space comfort conditions. (Reference 4)

Suspended radiant panel advantages include:

  • Commonly available in North America from a variety of manufacturers

  • Fits well and aesthetically into conventional dropped ceilings

  • Relatively energy-efficient

  • Fast-acting and can be used with conventional HVAC controls

  • Design guidelines for both heating and cooling are available

  • Easy to divide and control into discrete small room by room control zones as required

  • Easy to retrofit into an existing dropped ceiling system

  • Low maintenance requirements

  • Silent operation, temperature exchanges at the speed of light.

Disadvantages include:

  • Relatively high cost for large surface areas

  • Very light thermal mass, no ability to store and offset building loads to nighttime

  • Can be costly to relocate for tenant room revisions unless suitable flexible connections and provisions have been designed into piping system

  • Additional seismic restraints required for heavier suspended ceiling elements

  • Subject to damage in a fire or seismic event, but repairs are not extensive and system is easily accessible for repairs.

Applied capillary tubes

Applied capillary tube systems consist of very small diameter (3 to 4 mm) plastic tubing imbedded into walls and ceilings, usually in a layer of plaster finish. Commercially available capillary tube mats currently are manufactured only in Europe using proprietary processes, and are generally made from durable, recyclable polypropylene plastic. These can be imported to North America, but the costs are sometimes an issue on smaller sized installations.

Polypropylene also is not an oxygen barrier material, so any capillary tube system has to be separated from the metallic piping system by a stainless steel heat exchanger, and all the pipe accessories in the plastic piping system must be stainless steel or all bronze. The plastic pipe system does not require any chemical treatment, thus saving some capital and operating costs.


These systems are very popular and common in Europe, and are well understood by the building designers there. The concept is to maximize the radiant surface area of the room to use the whole ceiling, wall, or both, to provide a large radiant surface operating at very small temperature differences to the occupied space. This results in a very energy-efficient system, as the main mechanical plant equipment does not require operation at extreme setpoints to provide heating and cooling to the space.

These systems can be more energy-efficient compared to the suspended ceiling panels due to the increased thermal mass created by the plaster embedment, and contact with the building structure in many cases. This allows a lot more building mass thermal storage, which provides a more stable indoor climate. This also results in a relatively slower response time when a control valve modulates, due to the time it takes to warm up or cool down the thermal mass of the plaster layer, and building mass.

Typically a response time of 30 to 60 minutes or more are common, depending on the thickness of plaster and proximity to building structural mass. It is common to use slow acting pulse width modulation controls to operate these systems. Due to the relatively rapid heat gain and response time of these systems, a water chiller is required to provide sufficient cooling water during the daytime occupied periods.

Advantages include:

  • Can be installed to cover very large surface areas at relatively low cost (in Europe)

  • “Built-in” to the building finishes and completely invisible in the space

  • Can be integrated into a dropped ceiling or panels depending on interior finishes

  • Good energy efficiency

  • Relatively fast-acting response and can be used with conventional HVAC controls

  • Easy to divide up and control in small discrete thermal control zones as required

  • Conventional controls and low maintenance requirements

  • Silent operation.

Disadvantages include:

  • Limited availability in North America, high capital costs

  • Not easy to renovate or change for tenant revisions, high costs to renovate piping connections and ceiling layouts

  • Requires very clean water to fill the system to avoid plugging the small capillary tubes

  • Very little experience or design information available in North America

  • Very light thermal mass, no ability to store and offset building loads to nighttime

  • Severe fire or seismic event will render the system inoperable and require extensive repairs.

Fabricated PEX tubing systems

Fabricated PEX tubing systems consist of small diameter (1/2- to 5/8-in. diameter) tubes installed in wood or steel frame buildings (primarily residential construction) using factory-made grooved wood panels (Warmboard, Raupanel, etc.) and/or extruded or stamped metal plates to attach the tubing onto a wall or ceiling structure. The tubing system must have insulation behind it to make sure the radiant energy is focused toward the “emitter” face of the wall or ceiling. The finished sheetrock/drywall is then fastened over the tubing and it gets piped up to a warm water and cool water source just like a conventional radiant floor heating system.


This is an ideal compromise between the applied capillary tubes and the suspended radiant panels due to the relative ease of installation, relatively low costs, and use of conventionally available floor heating products. These systems don’t have as much thermal mass and can be a fairly quick-reacting system and can be operated by conventional zone controls. This system has very similar performance to the applied capillary tube system, but with the potential for a bit more “thermal striping,” somewhat attenuated by the metal conduction plates.

Advantages include:

  • Can be installed to cover very large surface areas at reasonable costs

  • Uses well-known conventional radiant floor heating installation methods and equipment

  • “Built-in” to the building finishes and completely invisible in the space

  • Good energy efficiency

  • Relatively fast-acting response and can be used with conventional HVAC controls

  • Easy to divide up and control in small discrete thermal control zones as required

  • Conventional controls and low maintenance requirements

  • Silent operation

  • Very long operational life; it lasts as long as the building structure.

Disadvantages include:

  • Not easy to renovate or change for tenant revisions, high costs to renovate piping connections and ceiling layouts

  • Very little experience or design information available in North America

  • Severe fire or seismic event will render the system inoperable and require extensive repairs

  • Very light thermal mass, no ability to store and offset building loads to nighttime.


REFERENCES:

4. Radiant Comfort Research Website at University of Arizona





No comments
Consulting-Specifying Engineer's Product of the Year (POY) contest is the premier award for new products in the HVAC, fire, electrical, and...
Consulting-Specifying Engineer magazine is dedicated to encouraging and recognizing the most talented young individuals...
The MEP Giants program lists the top mechanical, electrical, plumbing, and fire protection engineering firms in the United States.
Combined heat and power; Assessing replacement of electrical systems; Energy codes and lighting; Salary Survey; Fan efficiency
Commissioning lighting control systems; 2016 Commissioning Giants; Design high-efficiency hot water systems for hospitals; Evaluating condensation and condensate
Solving HVAC challenges; Thermal comfort criteria; Liquid-immersion cooling; Specifying VRF systems; 2016 Product of the Year winners
Driving motor efficiency; Preventing Arc Flash in mission critical facilities; Integrating alternative power and existing electrical systems
Putting COPS into context; Designing medium-voltage electrical systems; Planning and designing resilient, efficient data centers; The nine steps of designing generator fuel systems
Designing generator systems; Using online commissioning tools; Selective coordination best practices
As brand protection manager for Eaton’s Electrical Sector, Tom Grace oversees counterfeit awareness...
Amara Rozgus is chief editor and content manager of Consulting-Specifier Engineer magazine.
IEEE power industry experts bring their combined experience in the electrical power industry...
Michael Heinsdorf, P.E., LEED AP, CDT is an Engineering Specification Writer at ARCOM MasterSpec.
click me