By, Doug Carruthers 
In our article Warning: Graphic Geothermal Content we explained how to read and use the then new ‘Zone Load and Operating Profile Graph’ for design and sales. At the end of the article we made note of the fact that understanding the distribution of energy as a percentage of bin hours within an operating mode was the tricky part for many new designers and homeowners.
During equipment selection designers tend to fix on the % Sizing. % Sizing is important but it doesn’t tell the whole story. It simply expresses the equipment’s rated capacity as a percentage of the worst case peak heating load. It is a snapshot that doesn’t consider that there are very few hours in a year where the equipment will need to satisfy peak load requirements. Which begs the question, how do you really tell if equipment is undersized?
In his latest stroke of insight Ryan said: ‘Calculate the percentage of the total energy that is provided by the geothermal and display that directly below the heat pump’s percent sizing value.’
Seems obvious now... so we added the output "% Energy From Geothermal" to the zone pages and reports directly below '% Sizing'.
How Does This Help?
Well, now when you are selecting a heat pump that is ‘undersized’ for a space you can see that even though your equipment is sized to 75-80% based on capacity, the geothermal system may in fact supply 95-99% of the total heating energy required by the system. This makes it even easier for you to optimize your heat pump selections during the design. Plus, it gives you a quick way to explain to your customers why it is ok that the equipment you selected is ‘undersized’.
Think of it as a shortcut to explaining the bin hours on the ‘Zone Load and Operating Profile Graph’, which, in our humble opinion, is still one of the most useful graphical tools for understanding and explaining geothermal system operation.
Don’t Forget Operating/Installation Costs
It should be noted that just because the selected equipment is well matched to the space requirements, it doesn’t necessarily mean that it will be the cheapest to operate or install. Play around with combinations of multiple smaller units versus a single larger unit. What you find might surprise you.