Case Study

Transit Facility, Toronto

An example of the use of HGS for an 8500m² transit facility, near Toronto Canada shows the immense power of the algorithm

1. Building Demand Data

The hourly heating and cooling loads, shown here graphically, were first imported into HGS.

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2. Design Parameters

The user then enters cost and design data, such as the local electricity cost, and the heat pump COP, and software beings calculating the optimal supply mix between a Ground Source Heat Pump and conventional or secondary system.

3. HGS’ Peak Shaving Strategy

The software employs a peak shaving strategy, shown in the graphs below. It places a line across the demand curves, and calculates the economic outlook of having a GSHP meet the demand below the line, and an auxiliary system meet the remainder of the demand above the line. The software does this hundreds of times, moving the line up and down until it finds the mix of GSHP and auxiliary system with the best economic outlook.

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4. Optimized Hybrid Design

The software then produces an economics graph, such as the one below for the transit facility.

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α is the percentage of the peak demand that could be met by the GSHP for any given design. I.e., each value of alpha, represents a different possible design. The software user can easily see how the system installation costs (initial costs) increases with alpha, since more drilling is needed for a larger GSHP, and how the annual operating costs (Net present value of operation costs) decreases with alpha, since more electricity consumption is offset with a larger GSHP. The curve representing the net present value of total costs has a local minimum. This point represents the optimal design for the particular building.

5. Optimized by HGS vs. Standard Design Procedure

The table shows a cost comparison using different design strategies.

Peak cooling demand met by GSHP Ground Loop Length Net Present Value Initial Costs Payback Period
0% (conventional only system) 0 m $775,704 $51,141 N/A
48% (From HGS) 3317 m $709,252 $234,680 12 years
100% (GSHPs only) 5705 m $783,680 $374,294 19 years

Amazingly, using HGS has reduced the payback period from 19 years to 12 years! The system designer is empowered to demonstrate to the client, that installing an HGS-optimized system will save them thousands of dollars compared to doing nothing!