I promised to cover the hardware details of the numerous heat sources that will be incorporated into Hydronicahh in this series of articles. I will start with the solar thermal system.
This portion of the system will consist of two 32-sq.ft. flat plate glazed solar collectors, setup as a drain back system. These collectors will be tied to a 120-gal. reverse indirect DHW heater. The incoming cold water will first pass through a DHW preheat tank that is connected to the roof's trickle down cooling system. During the winter, this device may be bypassed due to a lack of available heat. From here, the incoming cold well water will then flow through a waste heat recovery heat exchanger that is connected to the building's main sewer drain. This heat exchanger is manufactured by GFX Technologies, www.gfxtechnology.com.
Through the use of this single waste heat recovery device, I reduced my DHW loads by a whopping 50% to 60%. That number is huge, and it basically tells me that I will have excess solar energy available to use for space heating through the numerous large surface hydronic based radiant emitters. Essentially, there will be very few BTUs that fall on the face of the solar collectors that are not utilized for either space heating or DHW preheating, which will result in a very high seasonal performance factor.
After the water has been run through the waste heat recovery heat exchanger, it will then be directed to the auxiliary DHW heating system, another reverse indirect, which will be backed up by a modulating condensing boiler, Lochinvar Knight model WB050, www.lochinvar.com, to bring the final water temperatures to an adequate temperature to avoid water borne pathogens, Legionella in particular. The auxiliary water heater storage tank will be maintained at 140°F, during occupied periods for sanitation purposes, but will be mixed down with an anti-scald mixing valve to around 125°F to the points of use. When the home is unoccupied, the DHW tank will be maintained at a minimum of 45°F. The Knight boiler will also serve as one of the space heating sources, but will be low on the list of available priorities due to cheaper, more renewable energy availability.
After extensive research into biomass wood gas generation units, I have decided to leave a place for it in my grand scheme of things. However, instead of utilizing that particular methodology immediately, I have decided to make my own wood-based heat generator, using my outdoor fire pit as the heat source. Who doesn't love an outdoor fire? This is one of those untried and unproven areas that is not an off-shelf application. I will be constructing the fire pit out of concrete lined with fire bricks with a conical shaped design. In the very center bottom of the fire pit will be a 6-ft. steel pipe to allow the introduction of combustion air into the center of the fire's combustion zone. A type K copper tubing heat exchanger will be imbedded into the conical shaped concrete fire pit to pick up the free radiant energy associated with the operation of the fire pit. There will be a pressure relief valve and oversized expansion tank on this loop to protect it from potentially dangerous high operating pressures, and there will be an uninterruptable power supply to insure pump operation in case there is a power failure, during an intense burn period.
The thermal energy produced by this system will be directed to two super insulated 240-gal. storage tanks, which are actually recycled LP storage tanks. There will be a remote flat plate heat exchanger to transfer the heat from the glycolized water in the fire pit loop to the non-glycolized water in the storage tanks, and a transfer circulator that will allow the wood-heated water to be the first priority energy available during demands for heat. If the wood fire pit heat source has completely maxed out the 480 gallons of storage at its maximum operating temperature of 180°F, then any excess energy will be diverted to the horizontal loop heat exchangers of the ground source heat pumps. This should raise the soil temperatures, which can then be extracted by the five- stage ground source heat pumps, and placed back into the loop of utilization. The fire pit will never be operated automatically, and if I do get hit with an inadvertent power shortage, I can snuff the fire quickly by dousing it with water to avoid any dangerous situations.
Please note that as I have explained, this method of heat production has not been tested, and I do not recommend that anyone else attempt to recreate this system without first consulting a qualified engineering professional.
Tune in next month as we continue our journey through Hydronicahh. Until then, happy high-altitude ground-source heat pump hydronicing.
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 720-479-9313.