Page 129 - Zero Net Energy Case Study Buildings-Volume 2

THE EXPLORATORIUM
CASE STUDY NO. 11
Heating, Ventilating and Cooling Systems
With all the historic preservation limitations placed on the standard ZNE design strategies for building envelope, daylighting and natural ventilation, the mechanical system for heating, ven- tilating and cooling provided the best opportunity for injecting high energy efficiency into the overall design. The ready availability of seawater from San Francisco Bay, in particular, led the design team to consider the use of high efficiency water-source heat pumps to produce heated and chilled water.
In addition, the requirement to strengthen the pier deck, and the decision to create a new con- crete floor slab for that purpose, provided another opportunity for even higher efficiency heating and cooling through the use of a radiant floor system. Using the high-efficiency heat pump sys- tem to generate the heated or chilled water, a high level of thermal comfort can be maintained at lower temperature setpoints for heating and higher temperature setpoints for cooling compared to air systems, thus lowering energy demand. This is a natural fit of these two types of mechani- cal system components, which are the basis of the system that was ultimately designed and installed. There were still many challenges for the designers to overcome, however, before these great efficiencies could be realized.
First of all, the cost of this system would clearly be higher than a standard heating and cooling system that would be the alternative, especially considering the special conditions created by the use of seawater and the related maintenance. The design team evaluated life cycle costs for the two approaches and determined that the heat pump system with radiant floors would achieve a payback on the extra investment in 7 to 10 years, including the special design features and ex- pected maintenance costs associated with the use of San Francisco Bay water, compared with the standard boilers, chillers and air systems.
The Exploratorium opted for the heat pump approach based on a number of factors in addition to the simple idea that the lease period was much longer than the payback period estimated for the system:
• The space requirement for the central plant equipment is much less for the heat pump sys- tem because of higher efficiency of the system and the elimination of any need for a cooling tower;
• Historic preservation restrictions would be triggered by the larger mechanical plant for the standard system, especially since the equipment would have to be located on the pier deck; • Use of natural gas boilers in the standard system would require additional solar photo- voltaic panels to offset the gas energy used (and carbon generated) if the Exploratorium wanted to claim complete ZNE performance, which is a project goal;
• The connection of the building’s energy system to the natural environment in the case of the heat pump system is part of the Exploratorium’s narrative, consistent with its mission of demonstrating such connections to the public.
Other challenges arose in the design of the system itself, which had to be executed at a very large scale and with great care for its impact on San Francisco Bay in the vicinity of the pier. The system as designed consists of eight 50-ton water-source heat pumps, located in a central plant area. Heat exchangers are required because of the need to separate corrosive seawater from the heat pump equipment; this equipment is actually visible to the public through a display window. (See illustration on opposite page.)
The design and specification of the overall system is similar to that used successfully in nearby public aquarium projects and was well known to the design team. With these designs, the sea- water is pumped up into the central plant area where the equipment is in a protected setting that is easily accessible rather than locating the heat exchange coils in the seawater where the equipment is susceptible to wave action and organic deposits.
Zero Net Energy Case Study Buildings, Volume 2
Construction photos showing installation of new structural concrete floor and tubing for radiant heating and cooling system (above). (Photos cour- tesy of EHDD Architecture)
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