Green Buildings

Recovering energy using HVAC heat pipes

Tuesday, January 7, 2014

Heat pipes can be used in a building’s HVAC system to recover energy from the warming and cooling phases. Both applications of the systems can result in significant energy savings for building owners.

Here, Mazen Awad of Heat Pipe Technology Inc. explains how the process works, and why building owners may want to take note.

How do you recover energy from heat pipes?

Heat pipes are simple air-to-air heat exchangers, which are comprised of metal tubes that are charged with a specific refrigerant when a vacuum is created.

Heat pipes recover heat by guiding it through phase change. On one side of the heat pipe system, which can be a tube or multiple tubes, there is a warmer air stream. The warm air heats the refrigerant, which boils as it extracts energy from the air stream. After the refrigerant becomes a vapour it travels to the cold side of the system, where the refrigerant undergoes a phase change and reverts to a liquid. The process releases the heat absorbed from the warm side by distributing it to the cold side.

How can heat pipes be used in a building’s HVAC system?

There are two applications for heat pipes in building HVAC systems. The first is in ventilation systems, where heat pipes recover energy from exhaust air to either precool hot summer air, or preheat cold winter ventilation air.

The second way occurs in hot humid climates. When dehumidifier heat pipes are wrapped around the cooling coil, the coil extracts more moisture from the air stream. The overcooled air, which is too cold for practical use, is then reheated to a more comfortable temperature before being supplied to the conditioned space.

Both applications can improve indoor air quality, as well as save building owners money. Savings can amount to 50 per cent of energy usage, which lowers the operating cost per square foot in a building. Heat pipes also have no moving parts, meaning they are reliable and require no maintenance.

How do heat pipes work at different times of the year?

In hot humid climates, wraparound dehumidifier heat pipes help extract more moisture from the air, thus reducing relative humidity in the space and making it more comfortable. If overcool/reheat is used to control humidity, heat pipes can save on the reheat energy.

In ventilation systems during the summer months, heat pipes can precool ventilation air, lowering the energy required for summer cooling. During winter, heat pipes can preheat the air, lowering the energy required for winter heating.

What types of buildings are using these systems?

Any building could use this system, but from an equipment standpoint, buildings must have central cooling and heating units to take advantage of heat pipe systems. Big users include healthcare, colleges, schools, institutional, hospitality and the military.

What is the maintenance like for these systems?

Because heat pipe are simple devises with no moving parts, it’s hard for owners to tell if they are working or not. Instrumentation is the key. Design engineers can specify temperature sensors that are hooked up to building controls that show temperature changes across those systems.

There is minimal maintenance required for these systems. Heat pipes need to stay clean, so proper filtration is important. Cleaning needs to be done on a regular basis, similar to coils that are installed in the same air stream.

Mazen Awad, B.Sc., is the senior vice-president of sales and marketing at Heat Pipe Technology Inc. He has worked with the company for close to 25 years. 

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