Using infrared heating

When considering a new heating system or modifications to an existing one, cost and efficiency are paramount. In addition to the actual cost of a system and the energy to run it, consideration must be given to decreased morale and productivity when workers are uncomfortable in their environment.

01/15/2002


Key concepts

Infrared heats by radiation, avoiding the drafts created by convection heating.

Major types of infrared heaters are quartz lamp and metal sheath.

Infrared heaters are particularly good for spot heating and high-bay areas.

Sections:
The draft effect
Spot or total heating?
Solving problems
Types of infrared heaters
Gas or electric?
Installation
Economy


When considering a new heating system or modifications to an existing one, cost and efficiency are paramount. In addition to the actual cost of a system and the energy to run it, consideration must be given to decreased morale and productivity when workers are uncomfortable in their environment.

Infrared heat can provide cost-effective solutions for a variety of heating problems. Like the sun, infrared directly heats people and objects. And, unlike forced-air heat, which is immediately diffused throughout an area, infrared heats specific areas consistently (Fig. 1).


Forced-air heaters warm the air by convection. Heated air rises quickly and is stopped only by a building's insulation. Infrared heaters directly heat people and objects, which then transfer heat back to the air by convection and secondary radiation. The result is a heating system that is efficient, cost-effective, and easy to control, while providing a comfortable environment.

The draft effect

When warm air blown from a forced-air heater travels more than 10-15 ft, the surrounding air dilutes it, and the temperature drops below body surface temperature. Any moving air that is cooler than body surface temperature is perceived as a draft. This "draft effect" explains why people feel cold at ambient temperatures when they would otherwise be comfortable.

Infrared heats people and objects without causing any air movement. With infrared heat, people receive radiant heat from overhead and secondary radiation from the floor, walls, and surrounding objects.

This secondary radiation is constant, unaffected by any air movements. The warmth that radiates from the floors is also critical for worker well being. If workers' feet are warm, they usually consider the temperature in the building as "comfortable."

The wind chill factor creates another consideration when designing a comfortable work environment. Open doors or semi-open buildings draw cold air in and allow warm air to escape. Even very low-velocity winds or drafts can drastically reduce comfort.

1-mph wind causes 70 F to feel like 60 F

2-mph wind causes 53 F to feel like 23 F

A forced-air heating system has to work hard to reestablish the desired air temperature in areas affected by drafts and open doors. Infrared heaters recover quickly because the objects in the building retain their heat and are less affected by air movement.

In buildings with poor insulation or high ceilings, it becomes difficult to maintain a comfortable temperature with forced-air heat alone. Ceiling fans help push the heat back down, but they also create blowing air and contribute to the draft effect.

Plant engineers can use infrared's direct heating ability to keep the work floor comfortable without causing a draft. The higher the ceiling, the more a building will benefit from infrared's direct heating of people and the work floor.

Buildings heated with infrared can maintain higher comfort levels at lower ambient temperatures. For example, a 50 F ambient temperature with direct infrared heating can be as comfortable as a 70 F ambient temperature in a drafty location.

Spot or total heating?

Spot or partial heating is one advantage of infrared heat. Specific areas of a building can be heated to a higher comfort level than can be attained by the ambient building temperature. Forced-air heaters cannot provide spot or supplemental heat, because convection heat is immediately diffused throughout the building.

Infrared's ability to spot heat can save energy. A low, energy-saving ambient temperature can be set for the entire building, while infrared heaters provide comfort heating in frequently occupied areas.

Solving problems

Infrared's ability to heat specific areas can be used on a wide variety of heating problems. For example, a large warehouse may require very minimal heating because workers are heavily dressed. In this situation, freeze protection may be all that is needed.

A low-watt density infrared heater has half the intensity of typical metal-sheath models. This allows lower mounting heights and precise heat in just the quantity needed. Low-watt density heaters can also be hung like fluorescent lights between warehouse aisles. This application avoids the problem forced-air heaters create when their ideal airflows are blocked by full shelves. Infrared is preferred wherever convection heater airflows might be blocked by large obstacles.

Large industrial buildings can be overly expensive or impractical to fully insulate. Typical structures with overwhelming insulation problems are very high-bay buildings with massive air changes, such as foundries. Infrared can spot heat selective areas where forced-air heating would not be practical.

Because they require less maintenance than forced-air heaters, infrared heaters are sometimes used in damp or dirty (nonexplosive) environments. Metal-sheath infrared heaters are waterproof and can be cleaned by simply disconnecting and hosing them with water. Electric infrared's drying capacity can be used to dry out damp buildings and protect valuable equipment from condensation.

Portable infrared heaters can be conveniently moved to the location where they are needed most (Fig. 2). Whether indoors or outdoors, they can be used in any position — upright, sideways, or face down.


Types of infrared heaters

There are two main types of infrared heaters, quartz lamp and metal-sheath. Quartz lamp heaters can transfer heat over a long distance and through drafty areas (Fig. 3). They are ideal for high or bay buildings as well as outside applications such as snow and ice melting on parking garage ramps, walkways, and entrances.


Metal-sheath heaters excel in indoor spot heat applications. These heaters are strong and impact resistant. Metal-sheath heaters with protective screens are extremely durable and ideal for use in areas where sudden impacts could occur. In semi-open plants, metal-sheath infrared heaters can directly heat frozen components, such as aggregate hoppers, and reduce material handling problems caused by freezing temperatures (Fig. 4).


Metal-sheath heaters can be cycled to hold a predetermined temperature. This allows for a greater comfort level and increases overall energy savings.

Gas or electric?

The choice between gas and electric infrared depends upon building design, installation concerns, and maintenance preferences. Gas radiant heaters should not be used in uninsulated or poorly insulated buildings because they produce water vapor that can condense on surfaces with temperatures below the dew point.

When gas heaters are used, byproducts of combustion are usually vented outside. This allows outside air to come in and increases the heating load. Nonvented gas infrared heaters should not be used with ceiling fans because the fans push noxious fumes down to the work floor level.

Electric infrared heaters produce no by-products of combustion and can help reduce condensation in buildings.

Both electric and gas infrared utilize energy 100%. Electric infrared converts 70-80% of input into radiant heat, while gas infrared converts only 40-60%. The remaining input energy becomes convection heat, which rises up toward the ceiling and must be recirculated by fans. Only the radiant heat can be directed as needed.

Installation

Determining the number and arrangement of infrared heaters for a given location is a job best done by an infrared heating expert. Understanding some of the installation basics, however, can aid in the development of heating plans.

Electric infrared heaters can be mounted from the ceiling or along walls and angled down into the room. With ceilings 10 to 25-ft high, metal-sheath or quartz lamp infrared heaters are recommended. On ceilings more than 25-ft high only quartz lamp infrared heaters should be used.

Electric infrared heaters can be mounted 3-24 in. from a nonflammable ceiling. Depending on size, most nonvented gas infrared heaters require at least 4-5 ft of ceiling clearance.

Whenever possible, occupants should be heated by infrared from two sides. A typical mistake when installing infrared heaters is to mount them directly overhead. Doing this only heats the workers' shoulders and the tops of their heads, while their lower body receives little or no radiant heat.

Thorough, comfortable heating can be achieved by angle-mounting metal-sheath heaters, using asymmetric reflectors in quartz heaters, or utilizing multiple-heater applications. Heat patterns can also be bounced off some walls to help achieve an even heat balance.

There are a variety of controllers available for infrared heaters. Metal-sheath heaters can be cycled to hold a preset temperature by use of a percentage input timer. Because metal-sheath heaters take approximately two minutes to warm up or cool down, the cycle can maintain a very steady, even heat. Quartz lamp heaters are normally zoned, allowing energizing of 25%, 50%, or 100% of the system.

Economy

Even if a building is heated by forced-air, there are many advantages and economies to using infrared. With supplemental infrared heat, the forced-air heat can be adjusted to provide a lower ambient heat level that is augmented by infrared heat. This results in both a cost and energy savings.

— Edited by Joseph L. Foszcz, Senior Editor, 630-320-7135, jfoszcz@cahners.com





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