The major difference between a gas-fired infrared heating system and a forced hot air heating system is the method used to create a comfortable temperature. Infrared heats the floor slab, the machinery and the people first and then the air by using all three methods of heat transfer:radiation, conduction and convection. The storage of the heat in the slab floor creates a low temperature emitter and a faster recovery time when large overhead doors are opened and closed.

With a forced air system, the hot air rises to the ceiling and stratifies, gradually working its way down to thermostat level so that the floor slab never becomes warm enough to be comfortable. It literally acts as a heat sink,draining heat from the air and from personnel standing on the floor. The ceiling area of a high bay building using a forced air system can be easily 30° to 40° warmer than the floor area.

In the same type building heated with an infrared system, the temperature is much more uniform and the loft or roof area commonly will be at a slightly lower temperature than the floor level . . . a good condition for minimizing heat loss. Comfort can be maintained with a lower air temperature that will reduce infiltration and heat loss through the walls and roof.

In addition, instead of adding Btu/hr capacity to a computed building heat loss based on the thermal efficiency of a forced air system, the capacity is normally reduced by as much as 20%, based on the mounting height of the infrared system.

An added plus is that an infrared system has minimal power requirements, needing electricity only for burner ignition,the gas valve and the draft inducer (where applicable).

It is, therefore, easy to see that infrared commonly will save 30% to 50% in energy costs over unit heaters, frequently even more.

First of all, there is a distinct difference between combustion efficiency and thermal efficiency. Combustion efficiency is determined by the percentage of fuel converted to usable energy given sufficient combustion air. In our tube heaters, we provide sufficient excess air to achieve complete combustion; therefore, 99.9% of all combustible constituents of fuel is converted to carbon dioxide and/or water vapor, and nitrogen (excluding trace compounds).

Thermal efficiency directly measures the flue losses based on CO2% in flue gas and flue gas temperature. For example,the LTU Series’ CO2% is 7-8.9% and the flue temperatures are below 350°F, which complies with the American National Standard. Given these two facts, the thermal efficiency of our tube heaters is 75 to 83%, depending on the model.

We feel that while thermal efficiency is a good measure for forced air heating systems, it is not the best measure for a radiant heating system. We think the best measure for a radiant system is its overall radiant efficiency.The amount of radiation received on the floor, not convective heat transfer, will determine whether it is a good radiant heater or not. The radiant efficiency of any gas infrared heater can be calculated with the following equation:

Radiant Efficiency = Radiant Output/Heat Input

Radiant Output is determined by: R = SEA (T4 – Ta4)
where

S = Stefan-Boltzmann Constant
E = Emissivity of Radiating Surface
A = Surface Area
T = Emitter Surface Temperature
Ta = Ambient Temperature

Our aluminized steel emitter tubes are calorized and the emissivity of these emitter tube is around 0.80 – 0.83.The emitter tube temperatures average 750°F to 800°F.With these given values, the calculated radiant coefficient (input/radiant output) of our tube heaters is around 65.2%.

An infrared heating system is always sized at a lower input capacity when compared to forced air(convection) heating.This is due to different modes of heat transfer (radiation vs. convection), thermal mass and minimal stratification between ceiling and floor temperatures. For retrofit purposes, provided the unit heaters are maintaining the desired inside design temperature at ASHRAE design conditions,the following reduction can be utilized when recommending an infrared heating system.

Type	Thermal Efficiency	% Reduction in System Sizing
High Efficiency Unit Heater	80%	32%
Convectional Unit Heater	62%	48%

Assuming that the ASHRAE heat loss for a building is 100,000 Btu/hr, then the heater selection for this building would be as follows:

	Infrared Heater	Unit Heater
Building Heat Loss:	100,000 Btu/hr	100,000 Btu/hr
Infrared Compensation Factor1: (for radiant heating)	0.85
Thermal Efficiency2: (for convection heating)		80%
Heater Input Required:	85,000 Btu/hr (100,000 x 0.85)	125,000 Btu/hr (100,000 / 0.80)

1. Infrared heat loss compensation factor based on 26’AFF mounting height (see section C).
2. High Efficiency Unit Heater for comparison purposes.

Depending on your particular application, you will want to consider the following six accessories for all series of Space-Ray infrared tube heaters:

1.Thermostat
2. Manual Cutoff Valve
3. Flexible Gas Connector
4. Second Stage Regulator if supply pressure is over 14″ W.C.
5. Vent Cap
6. Chain Kit with S hooks for hanging heater
For the ETS Series, also consider including a seventh accessory:
7. End Reflector Kit (optional, but recommended).

For the ETU Series, also consider including two additional accessories:

8.Two End Reflector Kits per heater (optional, but recommended)
9. U-Bend reflector (optional, but recommended)

For the RSCA and DK ceramic heaters, you will not need a vent cap.

No.The National Fuel Gas Code (NFPA54) and local codes require a minimum ventilation flow of 4 CFM per 1000 Btu/hr of heater input by either mechanical or gravity ventilation if the heaters themselves are not vented to the outside.This additional ventilation requirement increases the building heat loss and the fuel cost as indicated in this example:

CONCLUSION: It will require a 28% larger capacity unvented infrared heating system to satisfy the building heat loss and comply with codes. In addition, the fuel cost of the unvented infrared heating system can be as high as 28% more than the vented infrared heating system.