ASHRAE Journal - January 2009 - (Page 35) these often offset each other and are not likely to significantly change by adding a heat pump to a system. Electrical demand charges are a significant portion of most commercial electric utility bills, but they were not presented for simplicity. Adding a heat pump, which is expected to operate during even the hottest portions of the operating season, will increase the demand charges. However, because the heat pump’s cooling capacity is displacing cooling that a chiller would normally contribute, only the net difference between the power of the heat pump and the equivalent power of a chiller must be added to calculate the additional demand charge for the heat pump. In most cases, the increase in demand charges is normally less than 5% of the total use costs and has a relatively minor effect on the total economic evaluation. Green Technology Benefits For this facility, one option is to provide four 1,050 ton (3693 kW) chillers with a redundant 1,050 ton (3693 kW) chiller and two 13,500 kBtu/h (3957 kW) boilers with a redundant 13,500 kBtu/h (3957 kW) boiler. If the proposed 800 ton (2814 kW)/13,500 kBtu/h (3957 kW) heat pump is installed in lieu of the redundant chiller and boiler, and the four chillers are marginally increased in size to 1,133 ton (3985 kW) each, the full heating and cooling redundancy is maintained. The capital saved by not supplying either the redundant chiller or the redundant boiler can be used to offset the cost of the heat pump. Conclusion Reducing the consumption of fossil fuels to power HVAC equipment reduces the amount of CO2 emitted to the atmosphere. It is true that replacing a fossil fuel boiler with an electric drive heat pump causes the building electrical consumption to increase and this will increase CO2 emissions at the utility power plant. However, this is more than offset by the significant reduction in CO2 emissions by not burning as much fossil fuel to heat the building. Also, if the facility owners and designers are interested in obtaining LEED® certification for the building, the addition of a heat pump can help. The U.S. Green Building Council’s LEED rating system offers credits for exceeding the efficiency requirements of ASHRAE Standard 90.1. Substituting a heat pump for a hot water boiler helps to achieve this goal. Capital Constraint Solutions Water-to-water heat pumps have a COP of 3.50 or higher, while a typical hot water boiler has a COP of 0.85. That makes heat pumps worth investigating for many types of facilities. This article has examined some of the system design guidelines, energy consumption calculations, green technology benefits, and capital constraint solutions of a water-to-water heat pump applied in a facility that has simultaneous needs for chilled and hot water. Given the many benefits that heat pumps offer, it is possible this technology will soon become a design standard in hospitals, pharmaceutical plants, hotels, and campus utility plants. In spite of the tremendous economic and environmental benefits that heat pumps offer, designers may still find it difficult to incorporate a heat pump into an existing system, due to capital budget constraints. If the building owner is open to creative financing, then the additional equipment, facility, and design costs can be financed with future economic benefits. In new facilities, another approach to reducing the capital outlay is to eliminate or reduce the size of the redundant chillers by taking advantage of the chilling capacity of the heat pump. The Arizona hospital example can be used to demonstrate this approach. For this particular facility, the design loads are approximately 4,200 tons (14 770 kW) cooling and 27,000 kBtu/h (7913 kW) heating. Standard design practice for this criticalcare facility dictates that a plant with multiple chillers be installed to meet the design load and provide redundant capacity in the unlikely event that one of the chillers is offline for maintenance or repairs during a peak-capacity period. The standard practice is to use an “N + 1” redundancy approach. The boiler system requires N + 1 redundancy for the same reasons. January 2009 www.info.hotims.com/22183-135 ASHRAE Journal 35 http://www.unitedmetal.com http://www.unitedmetal.com http://www.info.hotims.com/22183-135
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.