This is a continuation of last month’s column on the hidden consequences of water and energy retrofit considerations.
I then refocusedmy attention to the top of the system, on the circulation return. I found some areas where the return was fluctuating between hot and cold, and more cold than hot. Interestingly enough, the main circulation return line did not experience the same fluctuations I was observing between the individual return risers. I began suspecting cross connections at the individual shower and bath tub fillers. In the mean time, the telephone in the front office continued ringing off the hook with irate seasoned citizens wanting to know when they would be able to get hot water.
The strange thing was that some parts of the building had excellent hot water, with no shortages or fluctuations. And even more strange, the restroom just outside of the mechanical room could not get any hot water to the lavatory faucets. None of this was making any sense to me or the installing contractor, so we decided to fall back and regroup, and look at the system as a whole. The pressure compensated shower valves have a pressure balancing spool inside whose function is to avoid hot water shocks if a toilet is flushed at the same time a person is in the shower. Those cartridges were rated for a maximum operating pressure of 125 PSI. The building had a pressure boosting pump on the incoming water main, and it was maintaining 150 PSI pressure. A quick check with the shower valve manufacturer found that if the pressure exceeds 125 PSI, that there is a real good possibility that the diaphragm that keeps the valve in balance could have been ruptured, and if it is ruptured, it will cause a cross connection between the hot and cold water lines.
At this point, roughly two thirds of the building was experiencing flat out shortages, or extreme fluctuations in hot water temperatures. I asked the building manager to make me a list of all units that were complaining, and whether the complaint was related to the kitchen riser, the bathroom riser, or both, and whether the complaint was a fluctuation or an outright shortage of hot water. I then developed a “map” of all of the offending apartments and their associated risers, and we began a unit by unit investigation, looking for failed shower cartridges. We would run the bath tub filler until hot water began coming from the faucet. We would then observe the tub faucet through the eyes of an infrared imaging camera. If the hot stayed hot, and the cold stayed cold, then we would open the hot water at the lavatory, and if the hot port of the shower valve went cold, we knew we had a failed, cross connected cartridge, and we would then replace that failed cartridge and retest with the infrared camera. We ended up finding around two dozen failed, cross connected cartridges throughout the building. We replaced all that we could find, and after nearly two months of hot water complaints, we were finally able to satisfy the hot water needs of the seasoned citizens. Once we had hot water flowing throughout the building, I reviewed the changes that had been made during the retrofit/conservation program in an effort to determine what had changed, and why they hadn’t realized that they had failed cartridges throughout the building in the first place.
The original system realized very little pressure drop on flow through the DHW system compared to the new system. The coils in the reverse indirect DHW generators have a significantly higher pressure drop on flow than would a large open vessel. Both systems would realize the same pressure drop on draw through the anti scald mixing station located in the mechanical room. The pressure boosting station had been a part and parcel of the system from day one, so nothing had changed there. As an interesting aside, there was a 10 horse power potable pressurization pump that was piped in parallel with the smaller pony pressure booster pump, and the transmission on the larger pump was not working, so when it was called upon, it was eating kilowatt hours, but was not producing any pressure differential. It was staged with a two stage control such that when demand exceeded the capacity of the smaller pony pump, the larger pump would turn on and the smaller pump would turn off. I permanently disabled the large pump and recommended replacement in the near future.
Tune in next month as we continue to look at the hidden consequences of energy and water conserving retrofit considerations. Until then, happy seasoned citizen hydronicing!
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