McQuay RPR User Manual

System Solutions From McQuay

McQuay Evaporative Condenser
Rooftop System

How can I benefit from the substantial energy savings of
evaporative condensing in a cost-effective, factory-packaged
rooftop system?

McQuay RoofPak™ applied rooftop systems can be specified
with an evaporative condenser, allowing you to benefit from
substantial energy savings at the reduced design and
installation costs of a factory-packaged system. Evaporative
condensers can save as much as 40% on energy versus air­cooled alternatives, and they often draw less energy than any
alternative HVAC system.

Features

• Seven sizes from 75 to 150 tons.

• Blow through (Model RPE) or draw through (Model
RDE) cooling.

• Modular flexibility with multiple filter, fan, coil, heating
and specialty equipment options to match strict
application requirements.

• Factory assembled and tested units minimize field labor
for installation and commissioning.

• Walk-in service vestibule with raised floor grate and drain
pan contains water connections and most electrical, water
treatment and refrigerant service components.

Benefits

Reduced Energy Consumption

• Up to 40% savings in condensing unit energy
consumption versus air-cooled alternatives.

• Reduced peak electrical demand at design conditions
allows unit electrical service to be downsized for lower
installation costs and electrical demand charges.

• Airfoil fan selections require up to 20% less energy than
competitive forward curve fans.

• Patented UltraSeal™ low leak dampers minimize losses
(0.5% at 1.5” external static pressure).

• Factory-installed variable frequency drives further reduce
energy consumption.

Designed For Long Life and Easy Maintenance

• Stainless steel spray enclosure and sump, copper tube
bundles and polypropylene spray tree provide superior
corrosion resistance.

• All refrigerant service can be performed inside the walk-in
service vestibule – away from compressor noise and
outdoor conditions.

• Sufficient space is available inside the service vestibule to
house water treatment equipment required to prevent
scale build-up and microbial growth.

• Easy removal and replacement of spray nozzles, condenser
tube bundles and sump reduce service costs and down
time.

McQuay RoofPak™ Evaporative Condenser Rooftop System

Model RPE (shown) – 75 to 150 tons (blow through cooling)
Model RDE – 75 to 150 tons (draw through cooling)

Evaporative Condensing Reduces Energy Consumption

Air-cooled condensers reject heat to the ambient dry bulb
(typically 95°F design) as air passes over the condenser
surface. Evaporative condensers use a water spray that coats
the condenser tubes (Figure 1). As air passes over the tubes,
the spray evaporates and cools the tubes down toward the
ambient wet bulb (typically 75°F). The lower condensing
temperature reduces compressor work and energy
consumption, resulting in lower electrical demand and
consumption. In addition, the electrical service to the unit
can be sized for lower amps to reduce installed costs.

Air-Cooled Condenser Evaporative-Cooled Condenser

Figure 1 – Evaporative condensers use the cooling effects of
evaporation to reduce compressor work and electrical demand
and consumption.

Typical Savings Versus Air-Cooled Rooftop
Systems*

To illustrate the savings generated by evaporative condensing,
consider a two-story shopping mall using several 125-ton
VAV rooftop units and occupied 365 days a year. Tables 1 to
3 show the McQuay RPE condensing unit savings if the mall
is located in Los Angeles, New York and Las Vegas.

Table 1 – McQuay RPE versus a typical air-cooled rooftop unit
for a Los Angeles area mall.

Conditions Air-Cooled

Design Ambient Dry Bulb/Wet Bulb 95°F/72°F 95°F/72°F
Electrical Consumption Rate (per kW Hour) $0.15 $0.15
Electrical Demand Rate (per kW) $24 $24

Efficiency (kW/ton) 1.15 0.85

Condensing Unit

Electrical Cost $30,200 $22,100

Percent Savings 27%

McQuay

RPE

Table 3 – McQuay RPE versus a typical air-cooled rooftop for a
Las Vegas area mall.

Conditions Air-Cooled

Design Ambient Dry Bulb/Wet Bulb 110°F/72°F 110°F/72°F
Electrical Consumption Rate (per kW Hour) $0.07 $0.07
Electrical Demand Rate (per kW) $8 $8

Efficiency (kW/ton) 1.40 0.85

Condensing Unit

Electrical Cost $19,042 $11,351

Percent Savings 40%

McQuay

RPE

Tables 1 to 3 show evaporative condensing savings of $5,500
to $8,100 (or 27% to 40%) of your annual condensing unit
energy costs versus air-cooled systems.* The superior design
of McQuay RoofPak applied rooftop air handling section can
significantly increase these savings with features that include:

• More efficient airfoil fan selections versus commonly- used
forward curved fans.

• Blow through cooling coil selection and Optimal Air
Temperature systems reduce design cfm and fan energy
costs.

McQuay RPE Energy Costs Are Competitive
With Any HVAC System – Even Water-Cooled
Chillers

Using the 0.85 kW/ton condensing unit efficiency, Figure 2
shows a comparison of a McQuay RPE evaporative condenser
rooftop system with a 0.55 kW/ton water-cooled chiller
system.* In this case, we assumed that the chiller system
would have constant flow pumps and that it unloads to 0.46
kW/ton.

The energy performance of the two systems is very
comparable (Figure 2). The RPE offers a significant part load
advantage and the chiller offers a small full load advantage.
Given that most air-conditioning systems operate at 60%
load or less over the great majority of a typical year, the
McQuay RPE may be the best equipment choice for energy
savings and installed costs.

Chiller Offers Minor Full Load Advantage

Table 2 – McQuay RPE versus a typical air-cooled rooftop for a
New York area mall.

Conditions Air-Cooled

Design Ambient Dry Bulb/Wet Bulb 95°F/75°F 95°F/75°F
Electrical Consumption Rate (per kW Hour) $0.11 $0.11
Electrical Demand Rate (per kW) $18 $18

Efficiency (kW/ton) 1.15 0.88

Condensing Unit

Electrical Cost $17,860 $12,375

Percent Savings 31%

McQuay

RPE

RPE Offers Significant Part-Load Advantage

Figure 2 – McQuay RPE unit versus a 0.55 kW/ton water­cooled chiller system.