One of the unique aspects of the Hawaii Gateway Energy Center (HGEC) is its design as a thermal chimney to provide cool, fresh ventilation to occupants. Read how this unique design and heat exchange keep the Hawaii Gateway Energy Center cool without conventional air conditioning!

Buildings that are designed with conventional air conditioning use chillers to cool the air and mechanical systems with fans and ducts to distribute the air to occupants.  To minimize energy costs, approximately 75% of the air is re-circulated and only 25% is fresh.  This situation is not healthy for occupants, and energy consumption is intensive. 

At the HGEC, air conditioning and ventilation are achieved in a very different and innovative manner that minimizes energy consumption and provides 100% fresh air.  The visitor center is designed as a thermal chimney, which moves air by convection without the need for conventional mechanical system components.   The “thermal chimney” components consist of the building, a below-floor plenum, and a separate fresh air inlet structure that is located between the conference building and administration building.  Cooling comes from the deep seawater that is circulated in coils suspended in the fresh air inlet structure.  The way the system works is shown in the diagrammatic building section below:

The sun heats up the copper roof, which in turn warms the air in the ceiling plenum(A) through convection.  This warmed air rises in the ceiling plenum and is allowed to move upwards and exit the building through cylindrical exhaust stacks(B) at the high end of the roof. 

As the air moves up and out of the “chimneys “, new air is drawn into the ceiling plenum from the occupied conference and administrative spaces below(C).  A well insulated ceiling keeps the heat generated at the roof from radiating into the occupied space below. 

As air moves from the occupied space to the ceiling plenum, new air is drawn into the occupied space through ventilation floor grilles from a below-floor plenum(D).  This in turn draws fresh air into the plenum from the supply air inlet structure(E).   Suspended in the supply air inlet are coils circulating cold deep seawater.  As incoming air is drawn into the inlet it passes across the coils and is cooled on its way to the occupied spaces. 

As long as the sun shines, the thermal chimney design constantly moves air into and through the building (creating a thermosiphon), continuously providing cool, 100% fresh air to the occupants.   The only energy required is a circulating pump that provides a once-through flow of cold deep seawater to the cooling coils.  

A side benefit of this system is the collection and use of non-potable fresh water that condenses on the surface of the seawater cooling coils.  This condensation enters a floor drain and is routed to a 1,000 gallon below-grade storage tank for use in landscaping irrigation and other non-potable purposes. 

The HGEC is a good example of an effective thermal chimney building design that conserves energy and provide superior indoor air quality to occupants.                          9-22-09

Related Information: http://www.ferrarochoi.com/sustainarch/NELHA/index.html