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Comparison of Conventional and Infrared Heating Systems

April 1987

The manufacturers of gas-fired, unvented, ceramic panel infrared  heaters advertise that fuel costs are 20% to 50% less with their systems in comparison with forced air heating systems.  Several churches in the Philadelphia area have installed these systems.

The manufacturers claim that their infrared heaters do not heat the air, as other heaters do, but rather they directly heat objects and people, similar to the sun's heating the earth.  They claim that the units provide equal comfort at lower thermostat settings, that there is less air movement and associated dust, and that there is less stratification of air in the heated space.

Energy comparison

We compared the heating energy consumption data from four church sanctuaries and one multi-purpose room to similar buildings in our database. The following are the BTU's per square foot per year for the five buildings heated with unvented, gas-fired heaters mounted high on the walls:




The average heating energy budget for heating for 20 other churches used for worship only is 58,890 BTU per square foot per year.  Therefore, it would seem that these infrared heating systems use about 31% less heating energy.

Before recommending gas-fired infrared heating systems in other buildings, ICE decided to test the performance of the two types of heating systems serving the same room.  The test was designed to simulate intermittent, rather than continuous, heating because houses of worship and multipurpose rooms are not used continuously.

The purpose of the test is to determine which system uses less gas to heat the gymnasium to 70 degrees F. during the test.

Description of the test facility

St. Ignatius Church is located at 43rd and Wallace Streets in Philadelphia.  In the St. Ignatius Elementary School, there are two heating systems serving the same gymnasium.

The gymnasium was built about 18 years ago.  The room is 61 feet by 100 feet and has a 23-foot ceiling.  The walls are brick outside and concrete block inside.  The roof is flat and supported by steel bar joists.  The floor is tiled concrete slab.

Description of the energy systems

There are two natural gas meters in St. Ignatius School.  One supplies gas directly to six Re-Verber Ray 60,000 BTU per hour ceramic panel infrared heating units.  There is a set of three units on each long wall.  Each set is controlled by a standard wall thermostat. A Greenheck CBX 24-3, 4,500 CFM roof exhaust fan is interlocked with the infrared heaters.  The fan is required by the heater manufacturer so that the products of combustion can be exhausted from the room.

The other gas meter serves a hot water boiler, kitchen range, and a domestic hot water heater.  The boiler is a Weil-McLain J11B atmospheric gas-fired, 1,650,000 BTU/Hour input and 1,320,00 output, sectional cast iron boiler with two circulators.  One circulator serves perimeter radiation in a two-story school, an the other serves the gymnasium air handler, a unit heater in the kitchen and about 8-feet of baseboard radiation in the boys' room under the air handler.

For the purpose of this test, the school circulator was turned off, the domestic hot water heater was turned off, the kitchen unit heater is turned off, and the convector cover was closed in the boys' room.  Gas was then used only to heat the water supplied to the gymnasium air handler heating coil.

The circulator serving the gymnasium air handler is a Wagner 0.5 horsepower, single phase, 1725 RPM motor which runs an Armstrong H53 pump.  The amperage at the motor starter is 3.3 amps at 220 volts.

The Bohn VD-10 air handler is located above the boys' room in one corner of the gymnasium.  The coil is Bohn UHF122-15TX54.  The motor is 2 horsepower.  The air handler was designed to delive 386,800 BTU per hour at 5,100 CFM with 38.7 GPM.  For the purpose of this test, the thermostat was disabled, the coils and filters cleaned, and the outdoor air damper closed.

Temperature conditions

Before and after each test, the following temperatures were noted:

  a. Outdoor air temperature
  b. Wall, floor and ceiling surface temperatures
  c. Dry bulb and wet bulb temperatures 60" above the floor in the center of the gymnasium.
  d. Readings at the two wall thermostats for the infrared units.

During each air handler test, the following additional temperatures were noted:

  a. Water entering and leaving the boiler
  b. Water entering and leaving the coil
  c. Readings at the two wall thermostats for the infrared units.

The school personnel were instructed to call ICE if there were any problems with the heating system.  They had given us a set of keys to the school.  We asked that they turn off the heat in the gymnasium after Saturday afternoon basketball practice.  Tests were made on Sunday mornings, starting at 8am or 9am.

Operating the temperature recorder

One temperature probe was mounted 67" above the floor at the center of the room.  The other was 60" below the ceiling, above the lower probe.  Each probe created patterns on a strip chart. An event recorder indicated the operating time of the air handler and infrared heaters with separate data on the strip chart.

Heating with the boiler and air handler:

Just before the test, the school circulator and domestic hot wate heater were turned off.  Since the tests were all conducted on Sunday mornings, no one was using gas for cooking.  The outdoor temperature reset control was adjusted to 140 degrees F.  The outdoor thermostat was set to a higher reading to assure continuous boiler operation.

While the air handler was off, the circulator was turned on to heat the pipes and coil.  The burner fired on low limit, and then shortly turned off on high limit.

The gas meters were read after boiler has finished firing this first cycle.  Then the air handler was turned on, and this event was marked on the strip chart.

The room was heated, and just after the lower probe measured 70o, the temperature recorder was turned off.  Drybulb temperature readings were then taken at 4" and 67" above the floor, both at the center of the room and two feet from center of each of the four walls, all in accordance with ASHRAE Standard 55-1981.  These readings were taken quickly with an electronic thermometer.

Then the air handler was turned off.  At that time, the gas burner in the boiler may or not have been operating.  If the gas burner was operating, the readings on the gas meters were taken when the gas burner turned off and the boiler water temperature had reached high limit.

If the gas burner was not operating, the circulator was allowed to run, and the burner was allowed to turn on and off one more time before the ending readings were made.

The pre-test and post-test data are written down.

Heating with infrared system:

The probes were set in the same way as for the test with the air handler.  The same pre-test temperature readings were made.  Both gas meters were read before the test began.  The infrared heaters and interlocked exhaust fan were turned on at the electric panel and remained on until the lower probe records 70 degrees F.

A that time, the post-test temperature readings were recorded in the same manner used for the air handler.  Then the heaters and fan were turned off, and the meters were read.

Summary of test results:




* Outside air temperature is the average of the pre-test and post-test dry bulb temperatures outside the building.

** Temperature rise is the average increase between pre-test and post-test dry bulb temperature readings for the center of the room at 67" and for the two wall thermostats.  For the first test in each series, the temperature rise is that which occurred only in the center of the room at 67".

Results

The tests were done on alternate weeks to compensate for weather conditions.  The duration of each test is defined as the elapsed time between the beginning of the test and when the room has reached comfort conditions.  The average duration for the two sets of tests was longer for the air handler, even though the average outdoor temperature was lower on those days during which the tests of the infrared system were conducted.  The amount of natural gas used per degree rise of inside temperature was about 1.0 CCF for the infrared system and about 1.3 CCF for the air handler system.
The amount of gas used was about 40% less for the infrared system.

The results of the tests confirm the conclusions gathered from comparing annual heating energy per square foot for churches with conventional systems and those with infrared systems.

Efficiency

The basic reason for less gas use can likely be attributed the poor combustion efficiency from an atmospheric-type boiler, which is further aggravated by oversizing.  The gas-fired boiler has a rated output of 1,320,000 BTU's per hour.  The air handler, however, is designed to deliver 386,000 BTU per hour to the gymnasium, or about 30% of the boiler's capacity.  A smaller, properly-sized boiler, located near the air handler, would likely eliminate the standby losses from the large boiler and the piping to the auditorium.

A less important factor is the heat loss up the chimney and from the heat distribution system.  The infrared system has no chimney and no heat distribution piping.

Air stratification

The manufacturers of radiant heat systems claim that their heating systems do not heat the air, but rather heat the objects in the path of the infrared rays.  Warm air rises, and the difference of air temperature between the lower temperature probe and the upper one measures of the stratification occurring in this room.

There was greater stratification of air temperature with the infrared system, indicating that the air was heated, contrary to the claims of the manufacturers.

Figure 1 shows the charts from the temperature recorder.  The dots for the two probes connected to the temperature recorder form two lines - one line for the lower probe and one for the probe near the ceiling.  With the infrared system, these two lines tend to diverge, indicating that the longer the system operates, the greater the degree of stratification.  For the air handler, the two lines tend to be parallel, indicating that the air is more homogenized.

Drawbacks of infrared heating:

Direct fired gas infrared heating systems use less heating energy, but there problems associated with these systems.

First, the sources of heat are glowing panels on the wall of the house of worship.  In the installations we have examined, the ga piping and electric wiring are clearly visible.  This type o installation creates serious aesthetic problems in beautiful sanctuaries.

Second, with steep temperature setback during unoccupied hours,the inside surfaces of churches become cold.  The unvented products of combustion include water vapor, which condenses on these surfaces, possibly causing stains and mildew.

Third, the heating system is mounted higher than conventional perimeter radiation.  The exhaust fan eliminates the warm air in the upper part of the building, which must be replenished with cooler air coming from the outside.  This tends to increase the stratification of air the room, which is confirmed by our data above.

Fourth, the ceramic panels can be noisy when they start and stop, and this noise can be distracting during prayer and sermons.

Conclusions:

The data from both the tests and from comparisons of annual heating bills show that ceramic panel, gas-fired heating systems use less heating energy than conventional systems.  With proper design and installation, these systems can be a benefit to congregations.  However, these systems can be unsightly and can increase humidity, stratification and noise levels in the house of worship.