directly heat the domestic water more efficiently and allow the maintenance staff to shut down their existing boiler plant in the warmer months. Metropolitan supplied a skid-mounted 98% efficient Navien condensing domestic heating system that modulates and heats the existing domestic tank without any short cycling. A unique feature of these units is the ability to cascade them for high-Btu applications. The system included eight tankless
Built in the 1800s, the 8,000-square-foot University of Illinois President’s Mansion is occupied by the University President and sits on 10 acres of land. During formal events, hot water, or the lack of it, was a constant issue — especially during graduation, sporting events and meetings. If more than three people showered at the same time, the hot water supply would run out.
During these events, hot water or the lack of it was a constant issue — especially during graduation, sporting events and meetings. If more than three people showered at the same time, the hot water supply would run out. The existing hot water heating
system consisted of two 100-gallon natural gas tank water heaters that were only 60% efficient when new, and lacked sufficient hot water even when the house was only partially occupied. Given the existing system was a
tank system, heating the water when the mansion was vacant was an expensive issue as well. Tank systems have an eternally lit pilot flame and will turn on to heat the water periodically even when demand is at its lowest, unlike a tankless system that only uses energy on demand. Also, as minerals are prone to build- up in the tank over time, the heaters sometimes become less and less efficient thereby adding to the energy costs. Metropolitan Industries replaced
the old tank water heaters with three Navien NR240A natural gas tankless water heaters, each with a Btu rating of 199,000. These new water heaters — installed in June 2010 — provide an endless supply of continuous hot water and with 98% efficiency, reduces energy costs associated with the Mansion. The systems are on a recirculation loop that saves an average of 12,000 gallons of water per year because the need to “wait” for hot water to arrive at the tap is eliminated. Since the installation, supply issues
have been eliminated and the costs of heating the water were drastically reduced.
Sunny Hill Nursing Home After reading an article written by
Metropolitan released in a trade magazine and also attending a
seminar conducted by Metropolitan Industries, the Maintenance Director of Will County approached HVAC Division manager Matt Brickey for his input regarding replacing existing commercial hydronic boilers with a skid-mounted Navien package. The nursing home used their
massive hydronic boilers to supply heat to their domestic hot water storage tank through an internal shell and tube heat exchanger. The problem with this configuration is inefficiency because the huge boilers would short cycle 24/7 due to satisfying the load quickly, turning off, and then turning back on again shortly thereafter due to a drop in domestic water temperature. Short cycling causes numerous
issues for a heating system. One, it causes more stress on the boiler components by constant expansion and contraction. Boiler parts will wear and fail quicker than their intended life cycle. The second issue is the amount of wasted heat energy that is thrown up the stack. Each time a boiler turns on, or off, it goes through a purging process. During this process, a substantial amount of energy is lost in the form of wasted heat when the boilers short cycle.
Metropolitan’s solution was designing a heating system that can
water heaters, a variable speed supply pump that circulates domestic water from the tank to the heaters, a control system that monitors tank temperature and adjusts pump speed accordingly by sensing the flow and all the necessary piping and valves manufactured on a prefabricated skid for a complete functional system. This system also allows for ease of installation by the contractor because field work is limited to making piping connections from the tank to the skid, bringing electrical power to a single point connection, and running the CPVC exhaust & intake to the outside wall. The anticipated natural gas energy
savings during the summer months is expected to be a whopping 50% to 75%. In both project examples, the end
user saved money because of reduced energy demand by using Navien condensing tankless water heaters. Metropolitan Industries stocks a large supply of these units in their shop ready for immediate delivery, and can fabricate large custom
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Pictured is a prefabricated domestic heating system skid consisting of eight 98% efficient Navien tankless water heaters, a variable speed supply pump that circulates domestic water from the domestic storage tank to the heaters, a control system and all the necessary piping & valves manufactured by Metropolitan Industries Inc. for Sunny Hill Nursing Home.
commercial systems for contractor installation. l
phc july 2011
www.phcnews.com
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