Open-Loop Heat Pump System/Process Water Use

Hi Kara, 

I haven't had a project with this type of system, so I can't answer from experience, but I did find other guidance within the credit requirements that elaborate a little more on the table. If you look at the Step-by-Step Guidance section, Step 5 states "Design equipment-cooling systems to limit or eliminate potable water use and to capture and reuse excess generated heat. Install air-cooled or closed-loop cooling instead of open-loop (i.e., oncethrough) systems for medical equipment. Redundancy for cooling in critical applications may be required; as emergency backups, consider recirculating systems, draining technology, and holding tanks, as well as nonpotable water sources for air-cooled vacuum pumps and once-through cooling systems."

At a glance, it would seem that the system you describe is what the credit wants you to avoid; however, if you look at the language above, specifically, it finishes the sentence with "...systems for medical equipment." To me, this complicates the sentence and confuses things in terms of application.  

Maybe someone else will be able to chime in with some more advice or experience, but if it were my project, I'd contact GBCI (http://www.gbci.org/contact) and ask them for clarity on the language. If you do this, please do let us know what the response is.

The open loop GSHP system you describe in no way goes against the intent of the prerequisite to "reduce indoor water consumption". The goal of this credit is to reduce the amount of potable water being used for 2 reasons: 1. Because water is a limited resource and we don't want to waste the water. 2. Treating and pumping water and sewage takes a lot of energy and we don't want to waste that energy. Running ground water through your heat pumps (or through a heat exchanger first) and then injecting it back into the aquafer doesn't waste water and doesn't waste energy. If you're fully balanced and able to inject all of the water you extract, the amount of water in the aquafer remains unchanged and no energy was used for treatment. The reason for the once-through language is to prevent people from frivolously using water that has been treated to drinking water standards (lots of energy), sending it all back to the sewer system to be treated again (even more energy), and reducing the amount of water available for other purposes (drinking, agriculture, rivers and wetlands, etc.). The worst case would be people running municipally provided potable water through their cooling equipment one time and then dumping it directly into a sewage system to be treated again.

I would think you could easily clarify this with GBCI and if they understood the system at all they'd allow it. We've done lots of these in old LEED projects, but that was before this prerequisite and I haven't tried it since. We aren't really seeing any open loops any more because of all of the maintenance issues. We're actually in the process of converting an old open loop system to a closed loop system right now. Clients / engineers we work with are generally choosing closed loop over open for the maintenance / reliability reasons, but assuming you're adequately grouted to avoid contamination between aquafers, I don't see much of an environmental benefit of closed over open. Some of our earliest projects would be designed to bleed ground water (dump it directly in the sewer when the ground temperature would get too hot) but this is no longer allowed by most regulatory agencies. A system designed to bleed would be exactly the kind of thing the prerequisite is trying to avoid so proving this is not your intention should be part of your explanation to GBCI.

That was way better than my response. Thank you, Nathan.