ASHRAE Journal - May 2023 - 28

FIRST PLACE 2023 ASHRAE TECHNOLOGY AWARDS
device within this heat pump, controlled by a local programmable
thermostat controller located within each
suite. Each heat pump's energy recovery device uses a
core type of heat transfer surface to separate the outdoor
and exhaust airstreams, providing an energy recovery of
more than 50% with minimal cross contamination. This
is separate from all other suite ventilation systems.
Zone air distribution effectiveness in common areas
has an Ez value of 1.0, meeting the ASHRAE Standard
62.1-2010's requirement of, " Ceiling supply of warm air
less than 15°F (8°C) above space temperature and ceiling
return provided that the 150 fpm (0.8 m/s) supply air jet
reaches to within 4.5 ft (1.4 m) of floor level. " Ventilation
air for amenity areas is provided through stand-alone
core type energy recovery ventilation units, providing
ventilation, per ASHRAE Standard 62.1-2010.
FIGURE 2 The wastewater energy recovery system.
Domestic Hot Water
Hot Water
Use
Warm
Drainage
Waste
Holding Tank
Cooled
Drainage Out
Heat
Recovery Unit
Domestic Cold Water In
Parking garage levels are ventilated through intake
and exhaust air wells, strategically placed to properly
ventilate across the entire garage area. Makeup air and
exhaust air are drawn across from opposite ends of each
parking garage level to effectively sweep air across the
garage to meet indoor air quality requirements.
In terms of building operations, a direct digital control
(DDC) building automation system (BAS) controls the
major mechanical equipment. This includes the domestic
water pumps, hydronic pumps, boilers, central heat
pump, main control valves, domestic water heaters,
wastewater heat recovery equipment, parking ventilation
and corridor pressurization makeup air unit.
Innovation
The project team used several innovative solutions to
recover and reuse energy to improve the overall efficiency
of the building and reduce energy consumption,
including the use of geothermal field technology.
28
ASHRAE JOURNAL ashrae.o rg M AY 2023
Recovered Heat
Water
Heater
Preheated
Domestic Water
Preheat
Tank
CASE STUDY
Often, the preferred type of geothermal system is
horizontal. This is relatively shallow-between 6 ft and
10 ft (2 m and 3 m)-with pipes routed horizontally
over a large nearby area wherever possible. Due to this
requirement, horizontal systems are typically suited to
large or rural areas. Because of 70 Gloucester's built-up
location and constrained footprint, a vertical geothermal
system was selected instead.
The heating and cooling plant contains a 200 ton
(703 kW), 2,400 MBH modular geothermal chiller, one
3,000 MBH (878 kW) and two 1,400 MBH (410 kW) condensing
boilers. The geothermal system supplies the vast
majority of the building's heating load and all of the 24/7
cooling load through a geothermal heat exchanger, with
a total unit capacity of 2,639 kBtu/h (774 kW) for cooling
and 3,420 kBtu/h (1002 kW) for heating.
The geothermal field comprises 64 boreholes that each
reach a depth of 600 ft (183 m), with a total length of
38,000 ft (11 582 m) of piping. The size was calculated to
use up the available footprint area of the parking garage
beneath the building, while also achieving a depth that
would provide enough heating and cooling capacity for
the calculated annual loads of the building. All buried
pipe is made of high-density polyethylene piping.
A propylene glycol solution, chosen to minimize
toxicity of the solution in the loop, is pumped through
the 4 in. (102 mm) borehole piping underground.
During summer, the geothermal water loop rejects heat
into the surrounding soil, charging the ground as a heat
sink. The ground is then a heat source in winter when
the geothermal water loop absorbs captured heat from
the ground.
The wastewater energy recovery system was another
innovative feature of the project (Figure 2). Heat energy
in the outgoing sanitary wastewater is reused to pre-heat
the domestic hot water before it's heated by the domestic
hot water heaters. The system circulates water from a
large sanitary waste retention tank, and extracts heat
using a refrigeration cycle. The heat is rejected into a
domestic water preheat tank, which the building's main
domestic water heaters draw from, as opposed to drawing
directly from incoming domestic cold water. This
design reduces the energy required to heat the domestic
hot water for the building and relieves some of the load
on the domestic water heaters.
For more information on this project, visit
https://tinyurl.com/JournalExtras.
COURTESY OF SMITH + ANDERSEN
https://tinyurl.com/JournalExtras http://www.ashrae.org
ASHRAE Journal - May 2023

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