The article “Absorption-Heat-Pump/Boiler Systems” (by James Pettiford, Erin Sperry, Melissa Wadkinson, and Fabio Spreafico, September 2010, http://bit.ly/hmS991) misses the point. In my opinion, any effort to improve energy efficiency must also improve economic efficiency.
First, the heating requirements of new buildings have been reduced dramatically by code and good practice. Thus, technical and economic justification of more-efficient and more-expensive heating systems is more difficult.
Second, the energy table in the article assumes a building is fully heated and ventilated 24/7 during winter. That rarely is the case; it inflates heating energy to make the system appear more attractive.
Third, no mention of the assumed internal heat gains is made. Many new buildings are self-heating, with internal heat gains to outdoor temperatures well below the authors' 54°F assumption, reducing heating-energy requirements.
Fourth, more-typical one-shift operation with night setback substantially reduces heating-energy consumption without changing first cost.
Fifth, in many buildings, the authors' concept requires the use of a hydronic heating system, rather than a unitary or electric heating system. With the low-temperature hydronic system suggested, the size and costs of distribution equipment are greater.
Sixth, no mention of the increased first costs, parasitic loads, and increased maintenance and service of the authors' system is made.
Lastly, no mention of actual applications in this country is made.
Larry Spielvogel, PE, FASHRAE
L.G. Spielvogel Inc.
Bala Cynwyd, Pa.
We recognize that more-efficient technologies often require greater capital investment. However, the hybrid concept described in the article can substantially reduce the cost premium for achieving the quantum leap in efficiency needed to reach the national goal of reducing carbon-dioxide emissions by 80 percent by 2050.
For certain applications, the hybrid system can achieve substantial capital-cost savings by reducing the size of ground loops or bore fields by up to 40 percent. Additionally, the cooling capability of the absorption heat pump can enable a considerable reduction in the capital-cost requirement of electric chillers, with the added bonus of reduced electrical demand charges during peak summer periods.
We recognize every building has unique heating- and cooling-load profiles that must be evaluated carefully for proper selection and sizing of HVAC equipment. The heat-pump-plus-boiler system offers the designer broader flexibility in meeting the thermal requirements of a building and the economic needs of the owner.
Many buildings with large internal heat gains during occupancy require significant heating at night and on weekends. While heating loads can be lower during short periods of non-occupancy, there will be abundant hours during which the absorption heat pump would accomplish its purpose of significantly reducing fuel consumption.
One especially notable feature of the absorption heat pump is that it can perform simultaneous heating and cooling. This could be especially useful in high-internal-heat-gain buildings in which some zones (or ventilation-air-preheating systems) require heating while others require cooling.
The absorption heat pump can produce 140°F supply water and, thus, function quite well within lower-temperature design criteria for thermal distribution systems.
We agree with a growing number of HVAC-industry members that smart hydronic systems provide an economically attractive means of providing thermal comfort and energy savings superior to that of traditional heating and cooling.
Thousands of buildings in Europe enjoy the benefits of absorption-heat-pump-based heating and cooling. The authors believe that we here in the United States should emulate the new, higher standards of performance that have been set abroad. In the coming months, we will seek to publish articles describing the results of field studies conducted in Europe.
We believe technology innovation can lead to even more efficiency in the use of precious energy resources.
James Pettiford and Erin Sperry,Fulton Heating Solutions, and Melissa Wadkinson,Fulton Thermal Corp.,Pulaski, N.Y.
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