Commercial Architecture October 2017 - 42

PROJECT

hvac
What if the solar collectors cannot provide any temperature
boost, as might be the case when the fog rolls in or during an extended rainy period? "The tankless system simply compensates for
what the solar system cannot provide," said Morehouse. Even extensive maintenance is not a concern, according to Koch: "We
have designed the tankless system with a bypass. If the collectors
must go offline, the heaters will still function on their own to meet
demand."
THE INSIDE TRACK

The ACCO organization is as enthusiastic about tankless water
heating as their counterparts at AvalonBay. Koch cites the energy
savings, of course, stressing the high turndown ratio of a multiunit system. At Hayes Valley, each heater has a minimum output
of 16,000 Btu/hr. at a flow rate of 1/2-gal./min. "If a tenant turns
on a hot-water outlet at 3:00 a.m.," he explained, "we can comfortably and efficiently meet that isolated demand without firing
all nine units." But a few hours later when many residents may be
Each building has 32 solar collectors connected to a pressurized, 1,950-gal. storage tank where the heat energy is stored, awaiting a
call for hot water. The solar collectors boost the temperature of the incoming water supply so the tankless water-heater units need not
work as hard to meet the set-point temperature of 120 F.

showering, the heaters' maximum outputs-199,900 Btu/hr./unit,
or nearly 1.8 million Btu/hr. for all nine-should be more than
sufficient to meet demand.
The modular configuration also streamlines installation and
maintenance, minimizing cost and inconvenience. All 18 tankless
units at Hayes Valley were installed by two ACCO plumbers in
two days, said Koch. Nor was an expensive crane needed to lift the
70-lb. units onto the roof for installation onto steel screens: "The
units are so light with no storage, the rooftop weight load was never a concern," he commented. "Plus, the screen mounts provide
our installation and maintenance crews accessibility to the front
and sides of each unit."
Likewise, if an individual tankless unit needs servicing, it can
be easily isolated and removed for repairs without depriving the
entire building of hot water. "Instead of using a crane to place a
large piece of equipment onto the roof," said Koch, "you simply
wheel the replacement model on a hand cart up five floors using
the service elevator."
The lone problem ACCO has encountered with tankless relates

the solar collectors boost the incoming water by only 10 to 20 deg.,

to the increased amounts of silt in the water because of the drought

with the system providing 30% to 40% of the heat energy required

in California. "Lower water tables throughout the state resulted in

to meet demand. In summer, that "solar fraction" jumps to 80%,

silt in the plumbing," said Koch. "So ACCO now equips all our

for a year-round average of 64%. Greenpoints become available

tankless installations with strainers that filter the incoming water

when the renewable-energy fraction reaches 40%, which is why

before it enters the heaters. Problem solved."

AvalonBay was interested in the SLP system.

So does tankless technology has the inside track for any com-

"The system is designed to produce 7,250 therms of energy,"

mercial project involving ACCO? That is certainly the case when

Morehouse continued. "With the water heaters having a thermal

the company functions as the design-build contractor from the

efficiency of around 96%, the system should offset approximately

outset of a project. In such instances, "we will likely evaluate that

7,552 therms of natural gas, or the equivalent of 40 metric tons of

project in a way that will lean toward tankless," said Koch.

carbon dioxide saved per year."

Morehouse is excited about the prospects for solar-and tankless-in California, as the state drives toward a net-zero energy goal
for new residential buildings by the year 2020. In fact, he expects
low-rise and mid-rise structures to be seriously considered for inclusion on the new net-zero stipulation. "Getting as efficient as

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possible is the central reality for every developer, designer, and
installer in our current world," he concluded. "Tankless is definite-

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ly something that will be seen as a great benefit to the overall effi-

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ciency of buildings, and we believe our solar-thermal system is an
excellent complement to that technology." CA

COMMERCI A L A RCHI T EC T URE

OCTOBER 2017

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