Geowell™ Technology > HVAC System Modeling & Performance Simulation

HVAC System Modeling, Performance & Simulation

ARB/Geowell is well known for its thermal modeling of geothermal standing column well (SCW) HVAC systems and seasonal simulation capability. The operational model of a SCW was developed and verified through numerous case histories, some of which are offered on this website. Key to success of the model is the utilization of the results of specific thermal testing at the site, which include (K,α,τ) “effective” thermal conductivity, thermal diffusivity and thermal relaxation characteristic, respectively. Without this information, one is left estimating performance from wells drilled in the vicinity, which can lead to inappropriate designs and costly corrections.

Simulation includes the geothermal well field design, the plate heat exchanger, the building heat pump characteristics, the building (hr x hr) anticipated block load, and the geothermal HVAC control system. All of these elements are required to properly simulate building HVAC performance. One note of caution: typical building load programs, such as ANSYS, DOE2, TRACE, etc, are good estimation tools for sizing HVAC equipment to meet peak loads by zone, but must be interpreted for actual use in any simulation.

The Figure above is an example of one such (hr x hr) simulation for the peak summer month of July. The graph gives representative well temperatures (supply, return and bottom-hole) in a simulation that includes the heat dissipation from 35 ton heat pumps whose capacity and energy efficiency ratio (EER) vary with entering water temperature (EWT). In this particular design, a 10% bleed was instituted as the supply (upcomer) temperature reached 75^ºF. It is noteworthy that by bleeding a small portion of the water returning from the building to a separate diffusion well, one is able to arrest completely the well temperature rise.