GEOptimize - GHX design

GCHP & GHX design consulting

The size of gas line needed to supply heat to a conventional heating, ventilation and air conditioning (HVAC) system can be selected from a chart. Likewise, a cooling tower or air cooled condenser can be selected from a supplier's catalog by referencing the peak dry and wet bulb temperatures. The selections are typically based on a peak heat loss / heat gain calculation for the project. If the selections can meet the peak heating and cooling loads, they will meet smaller heating and cooling loads the rest of the year...as long as someone pays the bills!

There isn't a catalog from which a ground heat exchanger (GHX) for a ground coupled heat pump (GCHP) system can be selected. The size and configuration of the GHX depends on the design and use of the building, design of the mechanical system and the land area available and geology of the site.

The goal of GEOptimize is to work with you and your design team to minimize the size and cost of the GHX and ensure the long term, efficient operation of the system.

Definitions

The Building: As the building is being designed there are opportunities to recommend changes that can have a significant impact on the peak heating and cooling loads of the building as well as the annual energy needs. Some of the changes that can have an impact include:

Glass specifications
Wall and roof construction
Lighting specifications and controls
Potential for connections to other buildings to build load diversity

The Mechanical System: While the design of the mechanical system is being developed there are opportunities to change the heating and cooling loads, as well as the annual energy loads of the building. Changes that can make a significant impact include:

Efficiency of the equipment selected
Distribution system design
Ventilation strategy
Domestic hot water production
Thermal energy storage - see IKEA case study and St. Pierre Church case study. You may also want to download an ASHRAE Journal article about the integration of energy storage with GCHP systems
Waste heat recovery
Hybrid options (fluid cooler, auxiliary heat source, solar thermal, alternate heat dissipation methods such as snow melt) - see IKEA case study

The Site & Geology: The land area available for construction of the GHX and the geology of the site is one thing a GHX has no control over. They have to work with what is there and develop a design that works efficiently with the building and mechanical system that is being built on the site.

Even though the site & geology are fixed, there are opportunities on many projects to give consideration to:

Different types of GHX (vertical, horizontal trench, horizontal bore, surface water and groundwater)
Integration of different GHX types (horizontal and vertical, vertical and surface water, vertical & groundwater, etc.)
GHX configuration (borehole depth, diameter, spacing, trench spacing, pipe size, pipe placement, grout specification, etc.)