Ground Source Heat Pump min water velocity

[trashcanman]

I am working on a GSHP project. A previous project the Arch wants to copy used two (2)water pumps/heat pump. The pumps pulled water from a piping supply loop and then discharged water back into a return loop. The main loop (going to wells and back)have no circulating pump. Thus, all water movement is by the small, inline circ pumps on each heat pump unit (fan, compressor, condensing & evap coil). It seems to me that with just 1 or 2 heat pumps running (with 2 or 4 water loop pumps running as well), that the water velocity in the wells would be low. What is the minimum recommended well water velocity for a closed loop system? I am speaking of a closed-loop type with a u-tube arrangement for each well. Thanks for the help.

 

[flyrfan]

There is no minimum velocity criteria in this instance, provided the water treatment is up to accepted standards. Just remember, the lower the velocity the larger the pipe size. You should be very sensitive to this.

However, you should target a maximum flow velocity of 8 FPS to minimize pipe size, pipe wall erosion & flow generated noise.

 

[GMcD]

There is also a requirement for a minimum flow velocity in the Canadian Standards to make sure you get turbulent flow in the pipe to maximize heat exchange. Anywhere from 3.5 to 5 fps is our design guidline.

Some resources:

http://www.geoexchangebc.ca/products.aspx

 

[paulcim]

The research experts I've spoken to recommend a minimum U-tube velocity of 2.5fps. That has become our office standard. If you plan to vary your loop flow (which I would recommend from an energy perspective) I would select a design point between 3.5 and 5fps as GMcD has suggested to ensure that you can still maintain good heat transfer under part-load conditions.