This is the final part of my series on the greening of the Jetson House, the iconic home that has been around since the early 1960s and has been seen by pretty much anyone who has driven the corridor of Interstate 70 between Denver and the western side of the Continental Divide. See Related Articles (below) for Parts 1 and 2.
The existing hydronic system was a mix of steel panel radiators, hydronic fan coil units and tube in concrete radiant floors. There are four zones of radiant floors. Two zones of fan coil units, eight zones of steel panel radiators and one zone of snowmelt. Each one of these loads would require a different water operating temperature based on demand conditions at the given weather conditions. The decision was made early on to utilize what I consider to be the state of the art modulating-condensing boiler, as manufactured by Lochinvar Corp. The control logic on this boiler is extremely flexible and allows for three different outdoor reset schedules, and allows for domestic hot water priority. Based on altitudinal derating requirements and appliance efficiency, two Lochinvar WHN 285 boilers were chosen. These boilers communicate between themselves through a two wire bus. Only one boiler was set up for the production of domestic hot water, and this boiler was dedicated as the lead boiler with the other boiler being the follower boiler. The master control logic that comes as a part of these boilers rotates the lead boiler with the follower boiler once it gets 50% more run time than the follower boiler, although all control decisions are still made by the designated lead boiler. This evens out the wear factors on the working components.
In keeping with the projects goal of energy conservation, the decision was made to utilize a variable speed, constant pressure circulator for both the low temperature radiant floors, as well as the higher temperature panel radiators distribution system. I used the WILO Eco for these applications. The actual control of the individual flow to the zones is performed via 24 volt zone valves. As the zones are called upon by the individual room thermostats, their calls are received and controlled by a conventional Taco zone valve control relay box. Depending upon which zone is calling, either high temperature or low temperature dictates which outdoor reset control program is initiated on the master boiler control. If a high temperature zone calls, and then subsequently a low temperature zone calls, the low temperature zone supply water temperature is protected by a thermostatic nonelectric control valve to limit the water temperature going to the radiant floor heating circuits. If only the low temperature circuit is calling, then that is the reset schedule used by the boilers control logic.
One key feature of the Lochinvar onboard control logic is the ability to share the load between the boilers. It is an adjustable feature that determines the point where the second boiler is brought on line. I set this feature for 60%. In other words, on any given call for heat, once the lead boiler reaches 60% of its capacity, the controller brings the second boiler on line, and lowers both units to 30%. This is done because these boilers thermal efficiency is the greatest when operating in the lower input regimes. As the load decreases, and the load becomes less than 60%, then it reverts back to single boiler operation.
An additional feature of the boiler control that was put into play is the alarm feature. If either of the boilers goes into a hard reset safety condition for whatever reason, a set of dry contacts will close. This set of dry output (alarm) contacts was connected to the homes’ energy management system, and if that signal is received, it immediately sends an e-mail to the owners cell phone notifying him that there may be an issue with the boiler system. The home will most probably be a weekend home, and will not be continuously supervised, so this feature is very important in making sure that his investment doesn’t end up in the middle of a crisis management situation due to no heat. With this system intact, the owners will be made aware of any potential situations long before pipes freeze and burst, causing the possibility of a significant property loss. In addition to the alarm contacts, the owner wanted the ability to enable the snowmelt system remotely. The home automation system has the ability to allow the owner to call the system up on the Internet, and turn the snowmelt system on. He can do this in anticipation of an incoming snow storm. As I’ve discussed numerous times, the snowmelt systems I’ve worked on and installed work much better proactively then they do reactively. We considered the possibility of installing an automatic control for the snowmelt system, but the homeowners are very hands on, and wanted as much personal control over the operation of the system as was reasonably possible.
In these days of budget conscious operations, this project proves that with the right conditions, that energy conservation can be performed on historically designated buildings, and not significantly affect the exterior visual esthetics of the project as a whole. This completes my series on the greening of the Jetsons’ house. Tune in next month as I relate a story about the leak detection job from hell. Until then, happy historically designated hydronicing!
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