Solar Hot Water and Space Heating System With Integrated Boiler

Overview

The overall design of the heat distribution system was done by Northeast Radiant Technologies of Gardiner, Maine.  One facet of their business caters to DIYers.  They also made suggestions on boiler specs that were passed on to George Phelps of Gilman Plumbing and Heating of Newport, Maine.  George worked with Quincy Hydronic Technology of Portsmouth, New Hampshire.

Installed system with boiler at upper left.

This system combines a 550 gallon drainback solar tank combined with a conventional propane fired boiler (Biasi Riva Plus).  The solar tank has two 60′ copper coils to heat domestic hot water and two 90′ coils for space heating.  Either part of the system can operate independently of the other or they can work together.  A temperature sensor in the tank is attached to a relay that cuts power to the boiler any time that the tank temperature is greater than 125 F.Read More

  This temperature was arrived at by running a flow test and determining that the DHW coil in the solar tank will deliver 120 F water continuously when the tank temperature is 125 F.Also the space heating coils will deliver essentially 125 F water to the input of the boiler.  Since this is above the normal temperature required for supply to the floor, there is no need for the boiler to run.  Both sets of coils in the solar tank can be shut off with ball valves, if need be, and then the boiler will provide DHW and space heating.The input and output of both sets of coils and the supply and return of the radiant floor have inline thermometers to provide information on system operation.  There are four SunEarth Empire EC-32 collectors, attached to the south wall of our log home, that have water pumped through them by a three speed Grundfos Alpha pump.  I have the pump set to operate at the middle speed. The pump is controlled by a Solar Thermal differential controller that senses the water temperature at the top and bottom of the tank and also the temperature of the air inside the collectors.  The controller is set to allow a maximum temperature of 140 F inside the tank. If the tank temperature is below 140, the controller is further set to start the pump any time the collector temperature is more that 16 degrees above the bottom water temperature.  The controller turns the pump off if the collector temperature falls to within 8 degrees of the tank water temperature. At this point all the water in the collectors drains back to the tank.  The controller has a safety feature which prevents starting the pump if the collector temperature is  above a preset upper limit to prevent steam generation.  The circulation piping has a Pentair flowmeter which shows water flow rate while the pump is running and acts a sight glass for tank water level when the pump is idle.

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The four Sun Earth collectors
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This system is used to provide heated water to two different types of radiant floor heating systems. One part of the heating system is the conventional Pex tubing in concrete floor in the basement area of the new addition.
The first floor of the addition uses Warmboard with Pex-Al-Pex under ceramic tile. The water is circulated through the boiler and the tank heat exchangers by a variable speed Grundfos pump.
The individual zones are regulated by thermostatically controlled valves. At the present time there are four zones working and plans are underway to install four more loops in the old part of the house. These will replace the existing forced hot air system currently in use.

Warmboard radiant floor heating.
System Schematic
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• System schematic diagram As shown in the schematic, all items in green are parts of the space heating side of the system and the items in red are part of the domestic hot water side.Read More

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  In normal operation valves 2,3,5 and 6 are normally open to allow water to flow through the respective heat exchangers. Valves 1 and 4 are normally closed.  If for any reason, it is desired to have the boiler operate without any boost from the solar tank, valves 1 and 4 would be opened and 2,3,5 and 6 would be closed.Pump A is part of the boiler installation and pump B is dedicated solely to pumping water to the solar collectors.Heat exchanger 1 consists of two 90′ coils of 3/4” copper connected in parallel.  Heat exchanger 2 has two 60′ coils but otherwise is the same as 1.The boiler that I used has a primary heat exchanger for space heating and a secondary for DHW.  Heat Storage Tank.  The tank was sized to accept a liner purchased from Tom Gocze at American Solartechnics in Searsport, Maine.    The inside dimensions are 55”x55”x48” h.  The tank is made from four panels for the side walls, a platform and a removable cover.  The cover is sealed on the edges with 0.5” round foam insulation to cut down on evaporation loss.    The construction of the tankverticallpanels, platform and cover are described below. panels, platform and cover are described below.