Bringing Solar Energy to Colorado

Consumer Center
Solar Spa & Hot Tub Heating


This page contains solar spa and hot tub heating system information. Diagrams are shown for two different systems along with a description of how each system works. In the field, variations on each system do exist. What we are presenting here are the basic generic systems

However, before deciding on a spa or hot tub solar heating system you should make sure you have a good tight fitting cover. With an outdoor spa or hot tub, a large amount of heat is lost due to evaporation, radiation, and convection. If you use a cover when the spa or hot tub is not being used the heat losses will be minimized. Using such a cover will therefore reduce the size of the heating system, be it a conventional or solar heater.

Collector Considerations for Spa and hot tubs - Because of the higher temperatures encountered with spas and hot tubs than with swimming pools, unglazed collectors are not usually recommended. When using glazed collectors to heat a spa or hot tub, the possibility then exists to install a combination system, i.e., heat a second system such as a DHW or space heating storage tank.

 
Please click on the system that is of interest to you.

Open loop drain-back spa - hot tub heating system
Closed loop spa - hot tub combination heating system

Open loop drain-back spa - hot tub heating system - This system uses a separate pump for the solar heat loop. This is because the water flow rate produced by the spa pump is to large for the small number of solar panels needed to heat the spa or hot tub. When the spa or hot tub does not require heat, the spa pump circulates water from the spa, through the filter, the standard spa heater, and back to the spa. If heat is needed and the solar system cannot supply it, the standard spa heater then turns on. The pump is usually
controlled with a timer but in this case, is also controlled by the solar controller so if solar can supply heat, the spa pump is turned off. In this case, spa water is pumped up through the solar panels and back to the spa. The check valve between the filter and the spa prevents solar heated water from feeding backwards through the spa filter. The check valve below the solar pump prevents the pump from losing its prime when the system is turned off. The small pipe (about 3/8" - 1/2" diameter) shown above the solar pump allows the water in the collector supply line to properly drain back into the spa through the collector return line. The air vent/vacuum breaker combination at the top of the panels allows the panels to fill and drain properly. The controller continually monitors the sensors located at the solar collector panel and
Open loop spa drain back heating system
the return water line near the bottom of the spa. When the temperature at the collector sensor exceeds the temperature of the spa water return line by a pre-determined amount, usually 8 - 15º F, the controller turns the solar pump on and the spa pump off. The pumps stay in this status until the temperature difference between the panel and spa return line sensors drops to about 3 - 5º F.

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Closed loop spa - hot tub combination heating system - The closed-loop-antifreeze
spa or hot tub heating system consists of three loops; the heat collection loop and the heat delivery loop to the spa and the heat delivery loop to the second system, either a DHW system or space heating system. Let's first look at the heat collection loop. Starting at the solar pump just to the left of the expansion tank, fluid will be pumped up to the collector panels. Here, the panels will absorb energy from sun and transfer this energy, in the form of heat, to the collection fluid. The fluid will then return down to the the 3-way diverting valve. Depending upon the valve's position, the heat collection fluid will either be sent to the spa heat exchanger or the DHW (or space heating) heat exchanger. At either heat exchanger, heat will be transferred from the collection fluid side of the heat exchanger to the cooler spa or DHW side. The collection fluid will then complete it's loop by flowing from the heat exchanger, through the check valve, and back to the solar pump. The job of the expansion tank is to allow for the expansion and contraction of the heat collection fluid
 Closed loop antifreeze spa/DHW heating system
as it heats up and cools down. The spa pump, just to the right of the spa will normally be controlled by a timer.

The controller continually monitors the sensors located at the solar collector panel and the return line near the bottom of spa. When the temperature at the collector sensor exceeds the temperature of the spa water return line by a pre-determined amount, usually 8 - 15º F, the controller turns the solar pump and solar spa pump on. The pumps stay on until the temperature difference between the panel and spa return water line sensors drops to about 3 - 5º F. The controller also monitors the temperature of the DHW (or space heating) storage tank. A comparison is also made between the tank's temperature and the solar collector sensor. When the panel sensor temperature is 8 - 15º F, the controller turns the solar pump and DHW (or space heat collection) pump on. Although it may sound as if both spa and DHW systems can run simultaeously, this is not the case. The controller has a priority switch on it and only one system will be heated at a time.

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Contact CoSEIA at any of the addresses below.

Main office -
8745 W. 14th Ave., Lakewood, CO 80215
Denver metro phone: 303 333-7342
Non-metro phone: 1 866 633-9764
E-mail: info@coseia.org		 CoSEIA Records -
PO Box 77, Como, CO 80432
Phone: 719 836-4804
E-mail: coseiarecords@hughes.net

This page last updated on 10-3-05