One of the major headaches for engineers and contractors in today’s complicated construction projects is properly balancing a multi-loop domestic hot water system (DHWS). Getting these systems properly balanced initially and having them stay balanced over the life of the building has, until now, been nearly an impossible job.
Furthermore, with today’s emphasis on more efficient building design and better operation and management, many practices of the past are no longer adequate or acceptable. No process or system can be ignored when looking for improvements. Even the seemingly simple task of supplying domestic hot water to all areas of a building requires another look to ensure that the most current and efficient methods are being employed.
In this article, we are going to take a look at DHWS, how balancing multi-loop systems works, and what some of the newest trends and technologies have to offer.
DHWSs are designed to keep the hot water supply at the desired target temperature and to minimize wait times and the wasting of water at the fixtures waiting for the hot water to arrive.
Note: The correct hot water design temperatures is a separate subject as to scalding verses Legionella control and is not a part of this article.
In order to have hot water at all locations, the circulator pump must send water through the system fast enough to overcome any heat loss of the circulating piping system. To ensure this target is maintained, the engineer selects the pump and piping so that the flow rate through the system is high enough to maintain the necessary temperature, but not so high as to cause excessive noise and potential pipe erosion due to excessive velocity in the piping.
Furthermore, the engineer must remember that the temperature drop across the system is dependent on the quantity of water circulated. See the ASPE Domestic Water Heating Design Manual for further data.
By Edward Saltzberg, P.E., CPD, FPE, FASPE & FNAFE