Design of Air-to-Air Heat Exchangers

• Highest Efficiency in Industry
• Seamless Air Channels
• Independent Plate Spacing for Each Airflow Path
• Certified Performance by Independent Test Lab
• Standard Operating Temperatures from -40 F to 220 F
• Optional Materials and Coatings Available for Special Requirements

Why Choose Heat-X-Changer?

Our heat exchanger's unique construction is a result of extensive engineering and research. The engineered airflow channels and close rib spacing provide maximum heat transfer among the highest in the industry - and versatile configuration options.
Heat-X-Changer's unique features include:

• Totally enclosed Seamless Supply Air Channels eliminate cross contamination of airstreams.
• Advanced Thermal Adhesive between plates and fins provides maximum heat transfer and withstands pressure differences of up to 15" w.g. without deforming air passages.
• Rigid Mounting of Plates eliminates settling or crushing of plates and allows for mounting the exchanger in vertical or horizontal configurations.
• 100% of Heat Exchanger Surface Can be Visibly Inspected and cleaned to ensure long term performance of the exchanger.

• Extruded Aluminum Separators provide a rigid, durable exchanger surface.
• Open Exhaust Air Channels enhance condensate drainage and resist frost formation, reduce fouling by eliminating obstructions that collect dirt or dust, and allow physical cleaning of exhaust airstream with brush or mild abrasive.
• Independent Spacing of Heat Exchanger Plates and Separators allows XeteX to provide custom exchangers to meet any pressure drop or performance requirements.

The standard heat exchanger unit is constructed of rigid thermally bonded plates separated by extruded aluminum spacers.

This unique cell assembly process eliminates exposed joints and provides a tight, leak-resistant seal. Cross contamination of supply and exhaust air is virtually eliminated.

XeteX's Heat-X-Changer heat exchanger is available in 11 standard sizes from 8" to 100" with over 30 different spacing options. For non-standard applications, the plates and separators can be independent sized to meet any special pressure drop or performance requirement.

Custom Designs

For special applications, our heat exchangers are also available in the following optional materials: epoxy coated aluminim, aluminized steel, stainless steel, and plastic.

Standard heat exchanger units are capable of operating at temperatures ranging from -40F to 220F. Custom built heat exchangers can handle temperatures up to 1000F where required.

Heat-X-Changer performance is certified by an independent testing lab according to ASHRAE Testing Standard 84-1991.

Configuration Options

XeteX's rigid construction of heat exchangers and crush-proof channels allow unlimited configuration options.

Single-Pass Unit with
Vertical Mounted Exchanger

Large Capacity Unit
with Double Heat Exchangers

Single-Pass Heat Exchanger

Single-Pass Unit with Horizontal Mounted Heat Exchanger

Vertical Unit with
Double-Pass Heat Exchanger

Indirect Evaporative Cooling with Water Spray System

Applications

Fresh Air Make-up

Increasing amounts of fresh air ventilation are required to satisfy state and local building codes. Heating and cooling these large amounts of ventilation air can be extremely expensive and, in some cases, cost prohibitive. Heat-X-Changer is the solution, bringing in the required amount of ventilation air at up to an 80% reduction in energy costs.

XeteX's heat exchangers can be custom-built to fit almost any process application, recovering exhaust heat and saving valuable energy dollars. Optional materials and coatings are available for high temperature or corrosive environments.

Indirect Evaporative Cooling

Indirect evaporative cooling is a process that takes advantage of the low cost of evaporative cooling without the additional moisture gained through direct evaporative cooling. XeteX's heat exchangers are ideal for indirect evaporative cooling since they have maximum
wetting area and can be completely sealed to prevent water migration into the supply air stream.

See Selection Procedures for an example of selecting an exchanger for indirect evaporative cooling using the effectiveness correction factors.

Double-Pass Heat Exchanger

For applications where systems run continuously or where utility costs are high, a counterflow double-pass exchanger is often the best option. The higher effectiveness (90%+) of the double-pass exchanger results in additional fuel savings which easily offsets the increased installation investment.

Fresh Air Make-up for Hot and
Humid Climates

The Dri-X-Changer precools the hot outdoor air and transfers that heat into the supply air for reheat. In comparison to a basic mechanical dehumidification system with reheat, the Dri-X-Changer can reduce the required air conditioning tonnage by up to 25% and overall energy consumption by over 40%.

Optional Heat Recovery Devices

Also available from XeteX are the following types of heat/energy recovery devices.

AIRotor rotary enthalpy exchangers are available for applications when recovering air conditioning energy is critical. The standard AIRotor recovers both sensible and latent heat with total effectivenesses of up to 80%. For more information on AIRotor, contact XeteX or refer to the AIRotor brochure.

Heat pipe heat exchangers are available on a custom basis to meet special conditions where there are high differential pressures or limiting unit configurations.

Plate Air-to-Air Heat Exchangers

FUNCTION:

Fresh air passes through one side of an aluminum plate and contaminated air passes on the other side. Multiple plates are joined together in a special configuration to form the heat exchanger. Heated contaminated air flows through one set of air passages while the cold fresh air flows at a right angle through alternate, intervening passages. Heat is transferred from the contaminated air to the fresh air but the contamination remains in the contaminated air and is exhausted.

Heat exchangers produced by XeteX, Inc. have become increasingly popular due to their:

• Reliable Operation
• Separate Fresh & Contaminated Air Paths
• High Energy Recovery (Effectiveness)
• Low Energy Usage (Low Pressure Drop)
• Low Cost

EFFECTIVENESS:

Effectiveness (Temperature Efficiency) is a measure of the amount of heat available in the contaminated air that can be recovered in the heat exchanger. The heat the would be exhausted is re-used by heating the fresh air without purchasing additional fuel. Effectiveness is expressed as a percentage of the maximum amount of heat available. This percentage varies between 45% and 85% (for a single-pass exchanger) depending on application and selection. Effectiveness is increased by selecting heat exchangers with large face areas (lower face velocities for longer dwell time), closer plate spacing (larger heat transfer surface) and double pass airflow (counterflow heat transfer).

Effectiveness is also influenced by several airstream factors. Higher Exhaust SCFM airflow relative to Supply SCFM airflow provides higher effectiveness in the supply airstream and vice versa. Maximum overall heat recovery usually results from equal airflow amounts in both airstreams even though effectiveness is apparently minimized with equal airflows.

Moisture in the exhaust airstream also increases effectiveness. When outdoor supply air temperature is low, moisture in the exhaust air will condense on the plates. Latent heat will then be transferred to the supply air. This heat transferred into the supply air is sensible heat (temperature rise heat only) but exhaust latent heat (changing from vapor to water without temperature change) is useful to increase effectiveness.

CONSTRUCTION:

The XeteX heat exchanger consists of rigid thermally bonded seamless aluminum air channels separated by extruded aluminum spacers. This unique assembly process eliminates exposed joints and guarantees a tightly sealed heat exchanger package.

This design, which uses high quality, pure aluminum , allows up to 20" w.g. differential pressure between the two airflows without deformation in the sheets. Continuous, reliable performance is assured in all element sizes.

XeteX's heat exchangers are available in various widths and heights. Larger sizes are made by combining several standard size cores into one larger exchanger. Our heat exchanger's unique design uses large rectangular exchangers with seamless contaminated airflow paths. This exclusive design reduces exchanger parts, reduces leakage, and enhances cleanability.

Standard design heat exchangers are suitable for operation temperature ranges of -40F to 220F. Higher temperatures up to 1000F may be obtained through use of metals designed for high temperatures.

Epoxy or Heresite coated heat exchangers are available to prevent exchanger deterioration in corrosive airstreams. The heat exchanger can also be treated with XSeal, an exclusive assembly process, to make the exchanger completely air- and watertight for applications where complete sealing is required, or to further increase cell rigidity.

Single Pass Unit

PRESSURE DROP:

The exchanger's resistance to each airstream passing through it is called Pressure Drop. It is measured as the difference between the entering and exiting Static Pressures through the exchanger for each airstream and is expressed in inches of water gauge (w.g.). The pressure drop through an exchanger is normally shown in relation to the velocity of standard air (SCFM) going through the exchanger. For an installation where equal amounts of air are supplied and exhausted, the SCFM and mass flow rate of each airstream will be equal but the actual velocities in the exchanger will vary with the temperatures of the air. The warmer exhaust air will have a higher velocity and higher pressure drop since it has a larger volume and must travel faster through the exchanger to maintain an equal mass flow with the supply air. The cooler supply air is more dense and has a lower velocity through the exchanger and a corresponding lower pressure drop.

Pressure drop should be kept reasonably low due to the larger fan horsepower and energy required to maintain design airflows. A doubling of pressure drop (PD) will double the required fan horsepower (BHP) (i.e. BHP = K x CFM x PD). Also, increased pressure drop tends to increase pressure differential between airstreams which can be undesirable.