Commercial Architecture October 2017 - 41

PROJECT

hvac

The twin-tower construction at Hayes Valley required the heaters be split into a pair of nine-unit systems. "A fully centralized system would have required
extending the water-heater return lines from one tower to another," explained design engineer Jeff Koch,
CPD, LEED AP, ACCO Engineered Systems, San
Leandro, CA, the company that designed the system
and installed the tankless units, in addition to the
waste and vent systems, storm drainage, and natural-gas and fuel-oil lines.
"By confining each system to its own structure, we
minimized the amount of return piping, reducing our
labor and making the overall system more manageable and efficient," Koch explained.
When a resident turns on a faucet or a shower, the

YOU CALL ME RAIN

tankless system at either tower senses the subsequent
water flow and activates the burner in one of the nine
rooftop units. If demand exceeds the capacity of that
initial unit, the system controller will trigger a second
tankless unit to fire, then a third, a fourth, and so on
until the need is fully met. As demand subsides, the
units shut down one by one.
The water supply itself comes through the solar-thermal system, which was designed and installed
by Sun Light & Power (SLP), Berkeley, CA. Also lobutes were apparent from the outset, AvalonBay still

cated on the roof, the system consists of 32 solar col-

had questions about tankless-primarily having to do

lectors on each of the two structures at Hayes Valley.

with the long term.

Each collector setup is connected to a pressurized,

"Because we hold onto the properties we build for
many years, the maintenance and the operations

1,950-gal. storage tank where the heat energy is stored,
awaiting a call for hot water.

sides of all these products and standards are very im-

When a demand for hot water arises, the so-

portant to us," said Susie Maglich, LEED AP BD+C,

lar-thermal system preheats the water supply through

director of design resources, AvalonBay Communi-

a pair of heat exchangers: the first between the collec-

ties. "So we wondered how the move from conven-

tors and the pressurized tank, the second between the

tional tank water heating to tankless would impact

tank and the municipal water that actually enters the

our Residential Services group.

tankless units. The latter operation is controlled by a

"For instance, we've learned that we need to flush

variable speed pump, a Grundfos MAGNA3, that cy-

these tankless units every year, and that flushing rou-

cles on and off with demand in response to the build-

tine is now part of our maintenance procedures. As a

ing's DHW demand. The glycol-water solution in the

result, tankless has become one of our preferred

collectors never comes in contact with the buffered

methods when we are pursuing LEED or Energy Star

water in the storage tank, and the latter never infil-

or wherever the local energy codes are particularly

trates the DHW supply, thus eliminating any poten-

stringent. We encourage our teams to go tankless to

tial concerns over Legionella bacteria.

help us achieve our goals."

HYDROTECH CALLS
ME OPPORTUNITY

The job of the solar collectors is to boost the temperature of the incoming water supply, so the tankless

INTEGRATING TANKLESS AND SOLAR

units need not work so hard to meet the set-point tem-

The installation at AvalonBay Hayes Valley uses 18

perature of 120 F, according to Martin Morehouse,

Noritz NCC1991-DV condensing tankless water heat-

solar-thermal engineer and estimator at SLP. "The

ers to meet domestic hot-water needs, including apart-

actual temperature boost the system provides varies,

ment sinks and showers, janitorial sinks, and even a

depending on the available heat in the storage tank,"

dog-washing area in the parking garage. The system is

which itself depends on the available sunlight.

a rooftop installation, capitalizing on San Francisco's

"During periods of low-to-moderate demand

year-round mild climate. The municipal water feed-

when the tank is hot, the solar pre-heat is able to meet

ing the tankless units is preheated by a solar-thermal

100% of the demand without the tankless units acti-

system to lighten the load, saving still more energy as

vating." [Note: A tempering valve caps the tank water

well as wear and tear on the heaters.

at the set point of 120 F.] During the cooler months,
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