Choosing between open-loop vs closed-loop ground source systems

As you start to investigate the world of ground source heat pumps, you’ll likely find that there are all sorts of decisions you’ll need to make about what your systems will look like. 

One of those can be choosing between whether to use an open-loop or a closed-loop system. Below, we briefly outline what each solution is, before providing some of their respective benefits and drawbacks, to help you make a decision.

What is a closed-loop system?

A closed-loop system is one in which liquid is pumped down into the earth to bring heat up in a closed system. That typically means that it is pumped down one tube into the depths of a borehole, then up another tube, before passing through the heat pump and the surface, and then repeating that same cycle over and over again. 

Benefits

The most significant benefit of closed-loop systems is that they are far more versatile than open-loop systems, and can be installed pretty much anywhere. This makes them a far more common choice. 

Drawbacks

Closed-loop systems are a lot more expensive to install. You often have to drill deep boreholes, and then bury hundreds of feet of plastic piping, a logistical feat that tends to cost thousands of pounds. 

What is an open-loop system?

With an open-loop geothermal system, you take groundwater directly from an aquifer, pass it through a heat pump, and then expel the water back into a discharge well, or a pond or drainage ditch. This water then enters back into the environment, passing back into the water cycle. 

Benefits

The biggest benefit of these kinds of solutions is their substantially reduced installation costs. You don’t have to bring a drilling rig to the property, drill boreholes, or install loops through which liquid can be pumped. If local environmental conditions facilitate this kind of system, it can be quite attractive for these reasons. 

Drawbacks

The main issue with open-loop systems is that they do depend on quite specific conditions. You need easy access to a steady aquifer that provides water at an appropriate temperature. 

Unlike closed-loop systems, they can be less reliable, with quality issues like silt or high mineral content impacting how well they work. 

Additionally, as you’re taking water from an aquifer, these kinds of systems are subject to many more environmental regulations. Even if you do have access to an appropriate aquifer, it’s very possible that local authorities won’t permit you to use it for these kinds of purposes. 

Ultimately, there are a whole range of calculations that need to be made when deciding which option to choose, and you’ll need to seek advice from a specialist service provider. 

However, if you do have access to a suitable aquifer for an open-loop system, it could very well be a good way of saving money on your ground source heat pump installation. It’s worth investigating further at the very least, as when combined with government grants, you could end up with a very affordable final installation figure.