Can anyone share experience/calculations for a closed loop laid into a stream, please? Our contractor suggests digging a pond beside the stream and laying coils into the pond. I picture maintaining a pond, (i.e., removing silt, keeping out passersby, etc.) could require a lot more than having the loop(s) in the base of the stream under a layer of sizeable rocks (to keep the tubing from being dislodged during high water flows). Experiences and opinions welcome, please! Thank you!
Are you the guinnea pig for this or has the contractor done it before? Nothing wrong with being the guinnea pig as long as the cost allows for a complete do-over to another type of exchanger if the pig runs off. If you are not the pig, talk to the people who have it allready and ask about happiness and comfort.
I'm drawn to the idea of exchanging heat with moving water... However, the problem with moving water is that, well, it moves...sometimes a whole lot. What happens in that stream during 10 and 100 year flood events? Do trees, couches, bathtubs, propane tanks and every other manner of human and natural debris head downstream at a gallop, tearing up everything in their path? Heavy stuff dragging along the bottom could shred geo loops no matter how well buried. Are there permitting issues with dumping "Sizeable rocks" in the stream? Rocks weigh less when underwater and shift easily in high currents. Conversely, does the stream ever dry out completely such as during a hot dry period? That could be a huge bummer for heat transfer at a time when you really need max cooling.
I'm glad you share my interest in moving water heat exchange! Our stream never runs dry. During downpours it rises and flows vigorously, but we are near enough headwaters that debris is no problem. Currently it is at a summer low with good flow; typical flow is ~4x current; downpour flow is probably 100x current. Permitting is a challenge we need to pursue. The Corps. of Engineers had to approve changes when the stream banks were improved. Using the stream is my idea vs. the contractor's preference to dig a pond beside the stream. I'm really anxious to learn of anyone else's experience using a steam vs. a pond, please!
I'll bite, it is an interesting idea. You may want to keep in mind that the temperature of the water is more important than the convection effect. The stream will be hotter in the summer & colder in the winter than water underground (thus 10 ft deep ponds will average daytime & night time temperatures over say, 3 days, weighted towards the more recent temperatures vs stream temperatures averaging say over 3 to 6 hrs [depending on depth of streams]). Also efficiencies are obtained in geothermal designs by having narrow delta T's at both ends (condensor & evaporator). In other words, the compressor is expecting 45-60F water not 35F & 80F water (see manufacturer's tables for actual water temps & COP or SEER values). Soooo, pond is probrably the better idea (but a 250 ft well/ton would have much more stable temperatures). Have fun!
While a pond may have more stable temps that is not the same thing as more favorable temps.... A glacial river cooling loops for a geo in July for instance would likely trump local pond loops........ So the answer would be found with a lot of other design detail. Most importantly to the observer, always remember when pros talk about loop efficiency, they mean you can get the btus you need with less feet of loop. This does not mean you will automatically spend less money heating or cooling your home. j
Stream loop geshoo - we have designed riverbed and streambed closed loops as well as designing a number of other stream related systems. The nature of the watercourse is important. How wide - how deep? Does it have an alluvial or gravel bed in the drainage either beside the stream or under it. Have you considered a stilling well or a weir/sluice gate? In the Dubois river, we permitted a jetty into the river and set plates behind the jetty - When permitting with the COE we called it fish habitat. Did the same thing with coils covered with Elk netting and large cobbles - they work well. Sometimes there is quite a bit of water in a gravel bed beside the river. We have built collection systems using slotted pipe or water well screen to collect and also disperse the water - A pump and dump if you will. I would be happy to talk to you about it.
