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ICM January-February 2017

Boiler Facts... George R. Carey, Jr. Vice President, Fluid Industrial Associates gcarey@fiainc.com twitter: @Ask_GCarey Why every home needs a DHW recirculation line People here in the U.S. are accepting the concept of using less—whether gas for their automobiles, electricity in the house, fuel to heat their homes— and people are throwing fewer things away and recycling more. The use of water also needs to be part of the “using less” concept. All of the major governing boards (American Society of Heating, Refrigerating and Air-Conditioning Engineers, American Society of Plumbing Engineers, Occupational Safety & Health Administration and the Figure 1. Traditional type hot water circulating system Veterans Affairs Administration) either have or are in the process of updating their codes and design criteria to address the subject. We are quickly becoming aware of the fact that this natural resource is not unlimited in its supply. Did you know that water covers 70% of the earth’s surface and that 97% is salty water and only 3% is fresh water? I am sure most of you have seen where local municipalities impose water bans or restrictions on water usage, i.e.; watering lawns, etc… Did you know that the average residential home (3 bedrooms/4 occupants) wastes about 12,000 gallons a year by simply waiting for hot water? In some of the larger homes, the waste can be as high as 20,000 gallons of water a year! In fact, based on about 25 million homes, almost 290 billion gallons of water are wasted every year! By educating your customer on the benefits of domestic hot water (DHW) recirculation, they will experience virtually instant hot water at all their fixtures, while conserving water. What is a hot water recirculation line? It is a pipe that is installed off of the hot water supply line after the furthest fixture in the home and piped back to the water heater. The line is very small, usually 1/2" and has a small bronze circulator installed on this line. The circulator circulates hot water back to the water heater and then re-circulates it back out to the furthest fixture. Now whenever someone opens the hot water faucet at a sink or turns on a shower, they no longer have to wait for hot water—it is “sitting” right there waiting to be used! That is another benefit to your customer—time. They no longer have to wait for the hot water which is a common homeowner complaint. Based on some average home sizes, length of run and pipe size, it is common to have to wait 1–2 minutes for the hot water to arrive. In addition to the inconvenience this causes, the waste of water is incredible. In fact, the American Society of Plumbing Engineers (ASPE) developed guide lines in 1998 to help promote conservation. Specifically the guidelines were: • Maximum distance for un-recirculated dead end hot water supply line branches is now specified as 25 feet maximum or a maximum of 31 seconds hot water delay time to any fixture • The use of low flow fixtures required by some municipalities increases the wait time for hot water at the fixture • 0–10 seconds = desired • 10–30 seconds = acceptable • Over 30 seconds = unacceptable A re-circulating line helps prevent waste and saves considerable time in waiting for hot water. It also saves money! Assuming 12,000 gallons of water are wasted per year, and using some average costs for water, fuel and sewerage costs, the total wasted water cost would be approximately $280. Four Things for Proper Sizing of DHW Recirculating Lines 1. The recirculation flow rate will be established by the hot water supply piping’s heat loss to the farthest fixture based on a given delta temperature. 2. The recirculation return line’s heat loss does not have to be considered. 3. The required flow rate to compensate for the heat 10 ICM/January/February 2017


ICM January-February 2017
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