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					Renee Hartley
ARCH 8831 – Green Construction
Homework #4

Radiant Floor Heating and Cooling

Premise of the Technology
          Radiant floor heating has been used for centuries. The Romans channeled hot air under the floors of their
villas as far back as 670 AD. The Romans were using radiant underfloor heating in 670 A.D. The principle was to
heat spaces by circulating warm water in tubes placed in the floor. That principle remains unchanged nearly 2000
years later. Other instances of radiant heating included the Koreans, who channeled hot flue gases under their
floors before venting them up the chimney. The Turks used stream water run through channels in walls and floors
to cool their palaces during the warm summers. In the 1930s, architect Frank Lloyd Wright piped hot water
through the floors of many of his buildings.
          Today, hydronic radiant heating systems circulate water or glycol solution through piping in walls, floors,
and ceilings to achieve space heating. While radiant heating is enjoying renewed popularity, especially in Europe,
using similar radiant technologies for cooling capacities are emerging as well. Radiant heating and cooling
technologies are based on premises of energy efficiency, human comfort, and clean and quiet operation.
          Radiant heating and cooling systems are more energy
efficient because they are based on radiation and (some)
conduction as the method for the transfer of heat rather than
convection. Radiation is the most efficient of the three heat
transfer modes. Convection is secondary and comes into play
only as matter interrupts or interferes with radiant heat transfer.
Radiant heat allows savings up to 50% compared to other
heating systems.1 Studies conducted by the American Society of
Heating, Refrigeration and Air Conditioning Engineers (ASHRAE)
indicate that with radiant heating systems people can be
comfortable at temperatures 6°F to 8°F lower than with convective systems .
          Forced-air and baseboard (whether electric or hot-water) heating systems are convective systems because
they use air as the primary heat-transfer medium.2 Radiant heat transfer is caused by a warm surface (i.e. the
warm floor) giving up its heat to a cooler surface (i.e. your body). This radiant energy travels through space
without heating the space itself. It only turns into heat when it contacts a cooler surface. Radiant heat and cool the
occupants and objects in a space rather than the air within a space. Because radiant systems warm and cool the
occupants rather than the room, people find they are comfortable at temperature settings several degrees lower
(with heating) and higher (with cooling) than with conventional systems. More moderate temperature settings
mean lower fuel costs and energy efficiency. In addition, human comfort is increased because radiant systems
virtually eliminate drafts since they do not rely on the movement of air for temperature regulation.
          Radiant floor tubing can also be used to cool a house, but presently it is only appropriate for dry climates.
The floor temperature is held at 68o F (20o C) by using either a small cooling machine (chiller) connected to the
floor tubing or the steady 55o F (13 o C) temperature of the ground by means of an earth loop. In arid climates, the
cool floor can be used to supplement or replace standard ducted air systems. However, in humid climates,
problems with over-cooling the floor could lead to wet slippery surfaces and fungus growth.
          There are three general types of radiant floor heat: radiant air floors (air is the heat-carrying medium);
electric radiant floors; and hot water (hydronic) radiant floors. All three types can be further subdivided by the type
of installation: those that make use of the large thermal mass of a concrete slab floor or lightweight concrete over
a wooden subfloor (these are called "wet installations"); and those in which the installer "sandwiches" the radiant
floor tubing between two layers of plywood or attaches the tubing under the finished floor or subfloor ("dry
installations"). Electric radiant systems are generally less expensive than hydronic systems. In addition, electric
radiant systems are better for spot-heating, conditioning a small part of a building, or for retrofits and renovations.
Hydronic systems are better for new, whole-house constructions and are generally much more expensive. There
are too many details and variables to discuss the variation of radiant heating and cooling systems and their
appropriateness for given situations further within this homework assignment.


1
    http://www.radiant-floor-heating.com
2
    Watson, Richard D. “Advantages of radiant heat”, Fine Homebuilding June-July 1992.
Environmental Benefits
         The most important environmental benefits of radiant heating and cooling technologies are energy
efficiency and improved indoor air quality. However, human comfort, quiet operation, and aesthetic considerations
improve the human environment within the building.

Energy Efficiency:
   1. The even heat distribution offered by radiant heating and cooling systems may result in lower heating bills.
       With radiant floor heating, you may be able to set the thermostat several degrees lower, relative to other
       types of central heating systems. This is due to the fact that radiant systems heat and cool occupants and
       objects rather than air, resulting in higher human comfort levels.
   2. Radiant systems may result in less infiltration of outside air into the house compared to houses with
       forced-air heating.
   3. Fuel and equipment savings: Radiant floor heating proponents claim that fuel savings of 15% to 20% over
       forced air systems are possible. For example, radiant floor heating allows for lower boiler temperatures,
       which may result in the boiler lasting longer (a 45 year life is not unusual). Radiant floors operate between
       85-140ºF (29-60ºC), compared to other hydronic heating systems' range of 130-160ºF (54-71ºC).
       Operation at a lower temperature may decrease the amount of fuel used.
   4. Less energy input: This is because it is much easier a task to pump water than it is to circulate air.
   5. The actual amount of energy saved is dependent on many factors, including how well the building is
       insulated, the building size, and whether or not the system takes advantage of free cooling.
   6. The zoning capabilities provided by radiant systems allow for the temperature of different rooms to be
       controlled separately. This allows for energy to be used only in the locations and quantities it is needed,
       instead of uniformly used throughout a building.
   7. Flexibility of fuel source: Radiant heating and cooling systems can be combined with many energy
       sources; natural gas, propane, oil, wood, electricity, solar, etc.

Indoor Air Quality:
    1. Radiant heating and cooling systems operate without forcing air movement to regulate room temperatures.
        Because of this, dust, dirt, and germs are not disseminated to other spaces and throughout the building.
        With no fans or blowers, radiant is dust-free, so it's also cleaner. Virus particles, bacteria and pet dander
        fall to the floor instead of circulating constantly in the air, so your family will stay healthier.
    2. Radiant heating does not dehumidify the air, so in winter, room humidity is more ideal. Unlike forced hot
        air, radiant heat will not dry out breathing passages or furniture.

Main Disadvantage: Condensation
           The main disadvantage of radiant heating and (moreso) cooling systems is that it is difficult to provide
latent cooling (dehumidification). Unfortunately radiant systems are probably not appropriate if used in conjunction
with operable windows in humid areas (like Atlanta), due to the possibility of condensation problems during the
summer months. Ways to counteract the formation of condensation do exist; they include control of water
temperature, utilization of drip pans, natural ventilation (appropriate only in non-humid climates), and dedicated
outdoor air systems.
         Since condensation of water occurs when the dew point temperature is reached, proper water temperature
control will help avoid any condensation. To prevent the formation of condensation, a sensor monitoring the dew
point temperature of the room is used in conjunction with a controller which modulates the inlet water temperature
accordingly. Therefore, if a risk of condensation is present, the water temperature is raised or the water flow is
shut off. However, because the panels do more work the lower the panel's inlet temperature is, the inlet
temperature should be determined to be as close as possible to the room's dew point temperature. Consequently,
the cooling capacity of a radiant cooling system is generally limited by the minimum allowable temperature of the
inlet water relative to the dew point temperature of the room air. 3
         Stated differently, radiant cooling capacity is limited by the cooling surface temperature being just above
the dewpoint of the ambient air in the space to be cooled. This means that the minimum effective temperature of
the radiant cooling surface in most building applications is around 16 C (61°F) to avoid the forming of


3
    http://www.twapanels.ca/cooling.html
condensation. The total cooling capacity of a radiant surface at that temperature is around 80 watts/sq-m (25
btu/hr/sq-ft). The corollary of that is that the building interior heat gains should be kept below 80 watts/sq-m (25
btu/hr/sq-ft) for the radiant cooling system to be effective. That's where the high performance building envelope
comes into play. 4
        In a residential application, the ability to open windows or doors would allow humid outside air to enter the
space. This could raise the dew point temperature to a point where to avoid condensation, the radiant panels
would have to operate at relatively high temperatures. Since the panel's cooling capacity is dependent on the
temperature differential between the panels and the room temperature, having to raise the panel temperature to
avoid condensation would severely hamper the panel's cooling ability.
        To ensure air quality and removal of the moisture load in the room, radiant cooling systems need to be
used in conjunction with a small ventilation system or dedicated outdoor air system. For more information on the
use of ventilation systems and DOAS, see www.naturalcooling.com.

Cost Implications
        According to the EERE, the cost of installing a hydronic radiant floor is approximately $4.00 to
$6.00 per square foot ($40-$60 per square meter). This fluctuates depending on the size of the room, the
type of installation, the floor covering, remoteness of the site, and the cost of labor.5 However, some
manufacturers claim lower costs. According to Radiantec, a manufacturer of radiant heating systems,
their rule of thumb pricing for all components needed in an average size home application is $1.50 -
$1.75/sq ft (NOT including the heat source).6 Depending on factors such as the type of system, the home's
heat load and local labor costs, installing hydronic radiant heat costs about twice as much as installing forced-air
heating. Electric radiant heat is more expensive to install, except in smaller rooms. An electric system for an
average-size bathroom costs about $400 to $700, compared to about $200 for a forced-air system (with the
furnace already in place). However, you will recoup the investment over time with lower energy expenses
(generally 10 to 40%).7

Construction Costs: Although the costs associated with the supply and installation of a radiant ceiling may be
slightly higher than a forced air system, there are other significant savings that should be taken into consideration.
The first and foremost saving is that of space. Because the required air volume has been reduced, the need for
large amounts of duct work above the ceiling has been greatly reduced. Plenum height could be reduced by
approximately one foot per floor. A reduction in plenum height can be translated into a reduction in overall building
height, which translates into significant savings in material and labor during construction.

Maintenance Costs: Maintenance costs are very low for radiant heating and cooling systems. Most maintenance
items center on the pumps and boilers. For the most part, the pumps used today are maintenance free. They use
water to lubricate the bearings, which allow for quieter, more efficient life span. Different boiler types will require
different maintenance. Less maintenance would be required for the air handling and air conditioning units due to
the reduction in size and load required by the building. Occasional flushing of the water or glycol solution in a
radiant system may be required as well. Glycol systems should be checked at least once a year to ensure the
system pH levels have not dropped below recommended levels.

Obstacles to Market-Wide Acceptance and Use
         Radiant heating is applicable in any region that experiences cool weather. However, radiant cooling
systems are best suited for dry, arid climates. Since humidity and condensation are concerns, especially in the
Atlanta region and much of the Southeast U.S., radiant heating and cooling systems are not catching on here.
Condensation can be a major issue in certain regions as well as in buildings that are not properly ventilated.
         Traditional U.S. building practices are a huge obstacle to market-wide acceptance and use of radiant
heating and cooling systems: In North America, we have become used to inexpensive dropped ceilings as the
mechanical and electrical service plenum, resulting in the use of overhead air distribution systems, and a great deal
of research into all-air comfort control systems has been done based on this configuration. Building owners are also

4
    “Radiant Cooling and Greenhouse Gases”    by Geoff McDonell, P.E.
5
    http://www.radiantec.com/whyradiant.htm

6
    http://www.radiantec.com/ballpark.htm

7
    http://www.radiant-floor-heating.com/
very concerned about initial capital costs, and most building design consultants are apt to stay with tried-and-true
system designs in order to minimize their risks.
         Another obstacle to acceptance may be a perception that an owner would need to install two sets of
radiant tubing systems for heating and cooling. Best place for radiant heating tubes is in the floor, while the best
place for radiant cooling tubes may be in the ceiling. Heat rises, cool air sinks. In a room, the coolest surface
ends up being at the low point where the coolest air is, therefore little natural convection takes place. Close to
half the output of a heated floor is from natural convection; cool air coming in contact with the warm floor,
rising, giving up heat and falling to be heated once again. Without the assistance of natural convection, floor
cooling capacity is about half that of floor heating. A cooled ceiling has much more cooling capacity than a
cooled floor because rising warm air will contact the ceiling, be cooled, fall to the room below where it will
absorb heat and rise to be cooled again.8
         Past failures may be another reason why market acceptance has been slow. For example, older radiant
floor systems used either copper or steel tubing embedded in the concrete floors. Unless the builder coated the
tubing with a protective compound, a chemical reaction between the metal and the concrete often led to corrosion
of the tubing, and to eventual leaks. Major manufacturers of hydronic radiant floor systems now use cross-linked
polyethylene (PEX) or rubber tubing with an oxygen diffusion barrier. These materials have proven themselves to
be more reliable than the older choices in tubing. Fluid additives also help protect the system from corrosion.9

Product Manufacturer Example
          KaRo Systems, based in Germany, utilizes a capillary tube system for radiant heating and cooling. The
capillaries are tiny, only 1/16” in diameter, and the entire system takes up less than one inch of height in a surface.
Therefore, the building owner experiences a space savings in addition to the environmental benefits of radiant
systems. The system is being widely used in European applications. See www.naturalcooling.com for more details
on the KaRo system.




8
    www.radiantpanelassociation.org

9
    http://www.eere.energy.gov/consumerinfo/factsheets/bc2.html

				
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