7.0 Rigid Heat Loss & Gain & Domestic Hot Water Estimates
The accurate sizing of GeoExchange systems is mandatory. The cost of a Geothermal heat pump system is approximately linear with performance. A geothermal heat pump installation that is oversized by a factor of two will nearly double the first cost. A fossil fuel heating system that has been oversized by a factor of two will add only about 25% to the cost. The oversized fossil system will fall short of achieving its published efficiencies because of short cycling.
The GeoExchange system is sized on the building loads for heating and cooling/ dehumidification. Although connected loads are an important consideration, the building itself places the loads on the earth. An oversized closed loop or well installation may become so expensive that the geothermal system would not be economically feasible. An under sized closed loop installation will fail at season extremes because of temperatures exceeding heat pump operational specifications. Well based or open systems may suffer the same fate, but are generally able to increase operational performance by pumping more water volume and increasing the bleed rate.
7.2 Requirements for Residential Facilities such as Prisons, Dormitories and Elderly Housing
Residential heating and cooling loads are universally estimated by a method known as Manual-J. Many states have recently adopted this estimating method as the sole source of heating and cooling loads for residences. Manual-J is a development of the Air Conditioning Contractors Association of America (ACCA) and derives its information from ASHRAE data. Hand derived Manual-J analysis tools are available through the ACCA headquarters.
Wright-Soft Corp publishes ACCA's version of Manual-J. Other organizations as Elite software and various manufacturers also have derived Manual-J analysis programs. Manual-J provides construction analysis, room-by-room analysis and over- _
view reports for the GeoExchange installer. frj
Heat pump equipment selection for residential applications is based upon the dominant load, either heating or cooling. Unlike air-to-air heat pumps the geothermal heat pump does not suffer from reduced performance, as the weather gets colder in the winter or hotter in the summer. Additionally, the cooler condenser in the summer yields cooler and better dehumidification on the evaporator side of the geothermal heat pump - even with some level of over sizing good dehumidification can occur with oversized cooling heat pumps. Some manufacturers have dual stage or dual speed compressors that allow approximately one-half the capacity of the heat pump during lower demand summer operation.
Figure 7-1 is an example of the Manual-J summary report and 7-2 of a construction report. The importance of the construction report cannot be overemphasized as a building not meeting the analyst's construction assumptions will not have an accurate heating and cooling design.
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