PERFORMANCE TANKLESS WATER HEATERS
LITTLE O
50% of hot water draws last one minute or less and 75% of all draws occur within less than 15 minutes of one another
.
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Behavioural studies show that tankless water heaters may be less energy effi cient than they fi rst appeared. Researchers Paul Glanville, Douglas Kosar and Jason Stair crank up the heat
ver the past decade, tankless water heaters (TWH) have garnered an increasing share of the North American gas-
fi red, residential water-heating sector in an otherwise stagnant market. Despite residential, gas-fi red storage water heaters (SWH) still being more prevalent than TWHs in North America by almost a factor of 10, roughly 20% fewer were shipped in 2012 than 10 years ago, while TWHs enjoyed a threefold growth during the same period1
For end users, the value is clear: water is
heated as it is demanded and, with little to no onboard storage, the standby thermal energy loss is negligible, leading to a signifi cantly higher effi ciency. Additionally, TWHs are sized with thermal inputs of up to fi ve times that of SWHs, and may be
controlled right down to 5% of maximum design output, making it possible for them to meet sustained hot water demands over a wide range of fl ow requirement. For these reasons – and others – end users appear to have gladly paid the higher installed cost for TWHs – relative to SWHs – which often led to the venting being upgraded and gas piping upsized. Tankless water heating is certainly not
a new technology, with European and Japanese manufacturers introducing
products to the US marketplace in the 1970s2
. But there are a number of factors
driving this current growth, including: ● Advances in water-heating technology
and controls establishing TWHs as high- effi ciency alternatives to gas-fi red SWHs, especially those with a condensing effi ciency greater than 90%
● New and prominent market drivers, particularly the enactment of Energy
Star for residential water heaters in 2009, followed by utility and government incentive programmes
April 2013 CIBSE Journal 39
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