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This project is the first of a four-phase programme to develop an integrated, gas-fuelled rooftop air conditioning system. The project's objectives were to develop a technical and economic performance database for a natural-gas-fired desiccant dehumidifier operating in a quick-service restaurant and to define the technical and economic performance characteristics required for such a system. A desiccant dehumidifier system using off-the-shelf equipment was designed and installed in a quick-service restaurant in Houston, Texas. The HVAC system and the building interior were monitored with a computer-based data acquisition system. The field test demonstrated that the basic rooftop air conditioning system does not maintain design conditions. Indoor relative humidity exceeded 80% while dry-bulb temperature exceeded 80 deg F (26.6 deg C). The natural-gas-regenerated desiccant dehumidifiers maintained the relative humidity at the 50% design point. The field-test desiccant dehumidifiers proved to be too unreliable for restaurant use, however. One of the units failed frequently due to problems associated with the controls and gas burners. The other unit generally operated satisfactorily. A technical and economic analysis of four HVAC system options utilising desiccant dehumidifiers in four US cities indicated either improved comfort control or energy cost savings compared with current HVAC practice, but generally not both. Also, the first cost of an advanced, desiccant-based HVAC system will have to be comparable to current equipment. Based on the field test and a four-city analysis of system options, technical and economic criteria for a commercial unit were defined. The field test of natural-gas-reactivated desiccant dehumidifiers in a quick-service restaurant demonstrated that (1) comfort control could be improved, (2) current desiccant equipment is too expensive and unreliable for the restaurant industry, and (3) even with improvements it is unlikely that market penetration will be realised unless first cost is low and/or a value can be assigned to improved comfort control.

KEYWORDS: gas fired, desiccants, dehumidifiers, roof mounted, air conditioning, performance, economics, databases, natural gas, restaurants, USA, heating, ventilation, monitoring, site testing, relative humidity, temperature.

Citation: Symposium, ASHRAE Transactions, vol.97, Pt. 1, New York 1991