ASHRAE Journal - August 2011 - 49

technology award case studies
delay, confirmation of liquid refrigerant ahead of the HRP and a soft start. The liquid refrigerant pressure was raised by a sufficient amount, to maintain its liquid state at the expansion valve without adding measurable heat. The compressor would then start just like it was summertime. That cured the building owner’s cold start issues. Now that the HRP was incorporated in the refrigeration circuit, we could allow the head pressure to float with the outside air temperature. So, instead of a fixed minimum head pressure of 225 psig (15.5 barg), we could operate the system down to 120 psig (8.3 barg). As head pressure falls, compressor capacity increases while power input requirements decrease. With an HRP in the circuit, there is no loss of net refrigeration effect because there is a 100% pure column of liquid refrigerant always available at the expansion device inlet. Therefore, solving the building owner’s winter start-up problems resulted in verifiable energy savings. As part of this upgrade, the owners asked if we had a method to shut off the compressors for the winter and still provide cooling, while staying within the same footprint of the chiller. In response to that request, we engineered the system so we could get a modest amount of “free cooling.” We accomplished this by shutting off and bypassing the compressors. While the compressors were off, we ran the HRP, thereby circulating liquid refrigerant into the chiller barrel. We witnessed a phase change and some cooling. We then added control points to the existing building DDC system, automated control valves and some additional piping. We also added a VFD to control the condenser fans and added a bypass circuit to allow the liquid refrigerant to enter the evaporator/chiller barrel without going through the expansion device. So, in the free cooling mode the direct expansion chiller became a close cousin of a flooded system. Not having a fixed head pressure takes some getting used to. On a hot day in July,
August 2011

Pre-retrofit
Condenser Fan No. 1 Condenser Fan No. 2

Discharge Piping

CHWR

CHWS

Pump Down Solenoid Valve

N/O

Filter Drier & Sight Glass Muffler Suction Piping

Evaporator Chiller Barrel

Expansion Valve Compressor

Figure 1: Refrigeration piping before hybrid refrigeration system installation.

Post-retrofit
Condenser Fan No. 1 Receiver Refrigerant Temperature In Pump Down Solenoid Valve Condenser Fan No. 2

Refrigerant Temperature Out

Discharge Piping

Liquid Level Sensor Discharge Pressure

CHWR

CHWS

N/O N/C

Bypass Check

N/O

Filter Drier & Sight Glass

N/C N/O

Evaporator Chiller Barrel
Liquid Level Sensor

Muffler Compressor

Suction Pressure Expansion Valve

HRP

Suction Line Accumulator

Figure 2: Refrigeration piping after hybrid refrigeration system installation. the head pressure may be 250 psig (17.2 barg). As the temperature drops toward evening, the compressor discharge pressures may drop to 140 to 150 psig (9.7 to 10.3 barg). As the seasons change, the pressures may stay at a steady 120 psig (8.3 barg) as the condenser VFD changes the speed of the fan motors. Eventually, the late fall or early winter temperatures cause the controller to shut down the compressor and isolate it. The system pressure once again falls to whatever the
ASHRAE Journal 49



ASHRAE Journal - August 2011

Table of Contents for the Digital Edition of ASHRAE Journal - August 2011

ASHRAE Journal - August 2011
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
2011–12 Presidential Address: Sustaining ASHRAE Through Leadership
Retrocommissioning Older Buildings
Liquid Refrigerant Pumping in Industrial Refrigeration Systems
Technology Award Case Studies:
Hospital Upgrade: Heat Recovery, Geothermal Save Energy
Cool Weather Savings: Using Hybrid Refrigeration Systems for Chiller Retrofit
Special Section
InfoCenter
Standing Columns
Solar NZEB Project
Emerging Technologies
Special Products
IAQ Applications
Washington Report
People
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - August 2011 - Intro
ASHRAE Journal - August 2011 - ASHRAE Journal - August 2011
ASHRAE Journal - August 2011 - Cover2
ASHRAE Journal - August 2011 - 1
ASHRAE Journal - August 2011 - 2
ASHRAE Journal - August 2011 - Contents
ASHRAE Journal - August 2011 - Commentary
ASHRAE Journal - August 2011 - 5
ASHRAE Journal - August 2011 - Industry News
ASHRAE Journal - August 2011 - 7
ASHRAE Journal - August 2011 - 8
ASHRAE Journal - August 2011 - 9
ASHRAE Journal - August 2011 - Letters
ASHRAE Journal - August 2011 - 11
ASHRAE Journal - August 2011 - 12
ASHRAE Journal - August 2011 - 13
ASHRAE Journal - August 2011 - 14
ASHRAE Journal - August 2011 - 15
ASHRAE Journal - August 2011 - Meetings and Shows
ASHRAE Journal - August 2011 - 17
ASHRAE Journal - August 2011 - 2011–12 Presidential Address: Sustaining ASHRAE Through Leadership
ASHRAE Journal - August 2011 - 19
ASHRAE Journal - August 2011 - 20
ASHRAE Journal - August 2011 - 21
ASHRAE Journal - August 2011 - 22
ASHRAE Journal - August 2011 - 23
ASHRAE Journal - August 2011 - 24
ASHRAE Journal - August 2011 - 25
ASHRAE Journal - August 2011 - Retrocommissioning Older Buildings
ASHRAE Journal - August 2011 - 27
ASHRAE Journal - August 2011 - 28
ASHRAE Journal - August 2011 - 29
ASHRAE Journal - August 2011 - 30
ASHRAE Journal - August 2011 - 31
ASHRAE Journal - August 2011 - 32
ASHRAE Journal - August 2011 - 33
ASHRAE Journal - August 2011 - 34
ASHRAE Journal - August 2011 - 35
ASHRAE Journal - August 2011 - Liquid Refrigerant Pumping in Industrial Refrigeration Systems
ASHRAE Journal - August 2011 - 37
ASHRAE Journal - August 2011 - 38
ASHRAE Journal - August 2011 - 39
ASHRAE Journal - August 2011 - 40
ASHRAE Journal - August 2011 - 41
ASHRAE Journal - August 2011 - 42
ASHRAE Journal - August 2011 - 43
ASHRAE Journal - August 2011 - Hospital Upgrade: Heat Recovery, Geothermal Save Energy
ASHRAE Journal - August 2011 - 45
ASHRAE Journal - August 2011 - 46
ASHRAE Journal - August 2011 - 47
ASHRAE Journal - August 2011 - Cool Weather Savings: Using Hybrid Refrigeration Systems for Chiller Retrofit
ASHRAE Journal - August 2011 - 49
ASHRAE Journal - August 2011 - 50
ASHRAE Journal - August 2011 - 51
ASHRAE Journal - August 2011 - InfoCenter
ASHRAE Journal - August 2011 - 53
ASHRAE Journal - August 2011 - 54
ASHRAE Journal - August 2011 - 55
ASHRAE Journal - August 2011 - 56
ASHRAE Journal - August 2011 - 57
ASHRAE Journal - August 2011 - 58
ASHRAE Journal - August 2011 - 59
ASHRAE Journal - August 2011 - 60
ASHRAE Journal - August 2011 - Solar NZEB Project
ASHRAE Journal - August 2011 - 62
ASHRAE Journal - August 2011 - 63
ASHRAE Journal - August 2011 - 64
ASHRAE Journal - August 2011 - 65
ASHRAE Journal - August 2011 - Emerging Technologies
ASHRAE Journal - August 2011 - 67
ASHRAE Journal - August 2011 - 68
ASHRAE Journal - August 2011 - 69
ASHRAE Journal - August 2011 - 70
ASHRAE Journal - August 2011 - 71
ASHRAE Journal - August 2011 - 72
ASHRAE Journal - August 2011 - 73
ASHRAE Journal - August 2011 - 74
ASHRAE Journal - August 2011 - Special Products
ASHRAE Journal - August 2011 - IAQ Applications
ASHRAE Journal - August 2011 - 77
ASHRAE Journal - August 2011 - 78
ASHRAE Journal - August 2011 - 79
ASHRAE Journal - August 2011 - Washington Report
ASHRAE Journal - August 2011 - 81
ASHRAE Journal - August 2011 - People
ASHRAE Journal - August 2011 - 83
ASHRAE Journal - August 2011 - Products
ASHRAE Journal - August 2011 - 85
ASHRAE Journal - August 2011 - Classified Advertising
ASHRAE Journal - August 2011 - 87
ASHRAE Journal - August 2011 - Advertisers Index
ASHRAE Journal - August 2011 - Cover3
ASHRAE Journal - August 2011 - Cover4
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