Maximum Entering Water Temperature
As previously stated, typical HVAC conditions call for an entering water temperature of approximately 95ºF (35.0ºC). All BAC Cooling Towers are capable of withstanding temperatures of at least 120ºF (48.9ºC) with standard fill materials. For applications where the entering water temperature exceeds 120ºF (48.9ºC) view the comparison table to determine whether alternate fill materials are required for your project.
At a military base in the Southeastern US, an energy services company (ESCO) has proposed to retrofit more than 1,000 family residences with geothermal heat pumps as part of an energy savings performance contract (ESPC). Each residence is to have one heat pump with its own ground heat exchanger consisting of two or more vertical bores. A design firm hired by the ESCO sized the heat pumps to meet peak cooling loads, and sized the bore fields to limit the maximum entering water temperature (EWT) to the heat pumps to 95 F (35 C). Because there is some disagreement in the geothermal heat pump industry over the peak temperature to be used for design (some designers and design manuals recommend temperatures as low as 85 F[29 C], while equipment manufacturers and others specify temperatures of 100 F[38 C] or higher) the authors were requested to examine the designs in detail to determine whether the 95 F (35 C) limit was adequate to ensure occupant comfort, efficient operation, and low capital and operating costs. It was found that three of the designer’s assumptions made the bore field designs more conservative (i.e., longer) than the 95 F (35 C) limit would indicate. In fact, the analysis indicates that with more realistic assumptions about system operation, the maximum entering water temperature at the modeled residence will be about 89 F (32 C). Given the implications of a bore field that is shorter than required, it is likely that other designers are using similarly conservative assumptions to size vertical bore fields for geothermal heat pumps.