IN MY DECEMBER 2001 column, I discussed the heating system that I’d installed in my own “live-in laboratory” (“Lessons I’ve learned from ‘Thistled House,’” pg. 24). I said near the end of the column that the system was slated for an update in the near future. That change was slated to be replacement of the heat source (a 40-gal., fully outdoor reset control logic, dedicated water heater) with one of the new, prototype wall-hung condensing boilers.
The change took place, and I’m here to tell you that the fuel savings associated with the switch are nothing less than phenomenal.
Not being one to leave anything to chance, and in exchange for the use of the equipment, I installed flow meters on the gas side that can electronically record each cubic foot of gas, along with a calibrated visual flow meter on the closed-loop portion of the hydronic heating system. I purchased an extremely accurate data logger and set about checking the appliance for true net thermal efficiency. The goal of all this was to prove or disprove all the industry hype floating around about the efficiency of this emerging technology. What I found is quite interesting.
The setup is connected to the previously described distribution system. The boiler is a Heat Transfer Products Model T-50 wall-hung condensing boiler. The flue venting was run inside my existing 8-in. B-vent flue, and the combustion air is being pulled through the annular space between the existing 8-in. B vent and the 2-in. non-foam-core PVC exhaust vent. Somewhat like a concentric venting setup.
There are two pumps. One for the production of DHW through a donated, experimental DHW storage tank provided by the good folks at Amtrol, and one for the space heating loop.
The boiler was ordered with the optional Vision 1 reset controls, which allow the boiler to operate around a floating set point that is dictated by a preset outdoor reset curve. The boiler modulates around this floating set point based on real-time loading, and other internal gains that affect the real-time heat load requirements. The flow rate through the space heating portion of the system is always fixed at 3 gpm, which is somewhat less than the manufacturer recommends but, remember, this is an experiment after all, and I wanted to see what would happen in the real world.
The burner has the ability to modulate down to about 18,000 Btuh, and can run all the way up to 80,000 Btuh during a DHW call, but typically limits itself to 50,000 Btuh during a space-heating call. The calls for heat are segregated by the Vision 1 control logic.
Modulation is accomplished through the use of a variable-speed, pre-mix blower. This assembly ensures accurate input control while maintaining high combustion efficiency through its full range. This methodology is going to become the standard for sealed-combustion, high-efficiency, gas-fired appliances.
By having all the monitoring equipment that I had strapped to this system, I was able to determine its net thermal efficiency to the minute. I saw numbers that ranged from 88% efficient during the DHW production, all the way up to 99% efficiency during low-temperature, low-speed idle conditions. The interesting thing was, and continues to be, the fact that even at design conditions the appliance rarely runs at more than low idle.
The Vision 1 kit can be monitored separately by a computer modem link that is supplied to Vision 1 dealers. It allows you to monitor the boiler’s operation in real time, showing all the critical parameters such as fan speed, supply water temperature, return water temperature, gas valve function, pump functions, DHW and outside temperatures. You have the capability, if needed, to review the fault history of the appliance to see what major faults the system’s on-board computer has seen since the appliance was programmed at the factory. A valuable tool for troubleshooting, for sure.
I’ve connected this link to my home PC permanently so that I can monitor the operation of the system at any time. I can also log a history of all the controlled parameters for any period of time my heart desires. While this feature was not intended to be used by the typical homeowner, I am not your typical homeowner, and I find the information provided to be fantastic. I could sit for hours, staring at the screen, watching it modulate up and down as loads come and go, and seeing it ramp up to handle DHW loads, then ramp back down to handle space heating loads. It’s a hydronic geek’s dream.
Back to reality. After normal operation, the system has consistently shown a 30% reduction in energy consumption when adjusted for weather differences. I find the fuel savings to be nothing less than fantastic when you consider what I was using as a heat source prior to the installation.
Tune in next month when I introduce my new way of heating my domestic hot water. Until then, Happy High-Efficiency Hydronicing!
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.