In a conventional closed loop system the pipes are buried in the ground. If a suitable body of water is available then it’s possible to consider a closed loop water collector. Instead of being buried in the ground the pipe array is simply sunk to the bottom of the lake, large pond or river. This reduces the cost of ground works required and can provide a more efficient solution.
The first thing that needs to be established is whether the available water source is suitable.

1. Lakes and ponds - There are two main issues with lakes and ponds, the size of the body of water (area and average depth) and whether water flows into and out of the lake. Many man-made lakes have streams flowing into them. This means that the water in the lake is quite regularly replaced even with a fairly small flow rate. This allows us to continue extracting energy from the lake for longer than if it was an entirely static body of water. A lake or pond with a flow can therefore be much smaller than a static body of water for a given amount of heat abstraction. The degree of shade created by trees around the lake or pond will also affect it’s suitability as a collector. The sunnier the better!

2. Rivers and streams - Flow is usually not the issue for a river or stream. Heat extraction is normally required during the winter months when more rain falls so water levels are unlikely to be a problem. Getting permission from the Environment agency can be more problematical for a river based collector. You may be able to divert river water into a suitable “sump” on your own land where it borders a river and use that as a pond to form the collector.

3. Sea - It is possible to use the sea for a closed loop collector. Gaining permission may present difficulties as may tidal flows and ranges. Careful planning and design is required.

Once we’ve established that the body of water is suitable then the detailed design of the collector can be carried out. There are a couple of approaches to installation of this type of collector. Coils of HDPE plastic pipe (diameter 32-40mm) are joined together on dry land (using fusion welding) and formed into a sort of raft that is then floated out into the lake. As the pipes are filled they sink to the bottom of the lake. They may be secured on blocks to keep them off the bottom and to stop them drifting off in strong currents. If the lake can be drained then this can make the installation process a little easier.

Another approach is to use so called “Slim Jim” collectors. These are in effect stainless steel radiators that are bolted together into the required sized unit to suit the heating needs of the system before also being placed on the bottom of the lake or river. These have the advantage of being easier to remove later for servicing, for example if a lake needs dredging.

Econic have experience of designing and installing closed loop water systems and can advise whether this approach would be suitable for your project.