Ten-mile Creek has been a major source of water for Helena since the early 1900’s. Due to amendments to the Safe Water Drinking Act passed in 1986, the Ten-mile Water Treatment Plant was constructed during 1989-90. The plant has a maximum capacity of 9 million gallons per day (mgd) with future provisions to allow for future expansion which could increase the capacity to 11.25 mgd. Flow through the Ten-mile system from the source to the consumer is entirely by gravity. The only pumping that is required is for the backwashing filters at the plant and to provide water for the treatment plant process plumbing.
The new water source heat pump (WSHP) system works as follows: Treated plant water (primary water) is pumped by variable speed pumps through one side of a double wall plate-frame style heat exchanger. The primary water flow is drawn from the clearwell by a new vertical turbine pump that sits on the concrete deck above the clearwell. After flowing through the heat exchanger, the water is delivered back to the clearwell. On the other side of the double wall heat exchanger, the WSHP fluid is circulated by variable speed in-line centrifugal pumps. Heat is transferred from the warmer clearwell water to the WSHP fluid within the double wall heat exchanger; the heat absorbed by the WSHP fluid is boosted in temperature by the heat pumps to a useable temperature (approximately 100˚F) which then is transferred to the facility through heating coils, fans, and air distribution ductwork.
Digital controls monitor water temperatures and vary the primary flow rate to ensure turbulent flow in the heat exchanger and prevent freezing within the heat exchanger. The secondary heat pump loop utilizes propylene glycol for subfreezing operation during cold primary (incoming water to plant can be as low as 33F) temperatures. Electric energy use for the whole plant has been reduced by 50%.