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PRO-C Series

The PRO-C Series

ASHRAE Standard 62 deﬁ nes the minimum outdoor

air ventilation rate required to achieve acceptable indoor air

quality. This standard, which is incorporated in all the U.S.

model building codes (BOCA, Southern, and Uniform),

recommends that outdoor air quantities be increased from 5

cfm per person to 15 to 20 cfm per person to avoid adverse

health effects. The increased ventilation air rates concern

many owners, architects, and engineers with regard to their

impact on humidity control, operating costs and construction

costs.

By recovering up to 80 percent of the total energy

normally exhausted from facilities, the PRO-C provides an

effective solution to the ventilation mandate. When a PRO-

C is combined with a Carrier rooftop unit, it allows for a

three-to-four-fold increase in the outdoor air quantity (5 to

20 cfm/person) without an increase in operating costs.

If a facility is designed to include unitary packaged

HVAC equipment or heat pumps, the addition of a PRO-C

is especially beneﬁ cial. In addition to reducing the cost of

operation, the PRO-C system greatly improves humidity

control; something that is important for providing acceptable

indoor air quality.

Preconditioning and Good IAQ

The PRO-C Series Energy Recovery Ventilator is an

outdoor air preconditioner speciﬁ cally designed to reduce

the energy required to cool or heat the outdoor air by as

much as 80 percent. The PRO-C also allows the Carrier®

3 through 12.5 ton HJ, TM, and TF rooftop air-conditioner

systems to effectively and economically accommodate the

three-to-four fold increase in outdoor air quantities, which

is recommended by the ASHRAE Standard 62, Ventilation

for Acceptable Indoor Air Quality. This unique capability allows

both new and existing buildings to beneﬁ t from healthy

indoor environments.

The PRO-C is designed to improve humidity control

when combined with the Carrier rooftop equipment. Because

the unit preconditions the incoming air to the packaged

equipment, the required refrigeration capacity can be reduced

by as much as 50 percent. Thus, the costs of the PRO-C

and its installation are typically offset by the reduced size of

the Carrier system. Generally, any ﬁ rst cost premium is paid

back within the ﬁ rst year of operation.

Humidity Control and IAQ

Unitary air conditioner and heat pump units are

controlled by temperature. When space conditions are

satisﬁ ed, the cooling coil or heating source is cycled off.

Since the ASHRAE Standard 62 recommends the continuous

supply of outdoor air, then warm/humid (cooling mode) or

cool/dry (heating mode) outdoor air is dumped directly into

the occupied space during those times.

As the outdoor air load changes, humidity levels can

ﬂ uctuate signiﬁ cantly with unitary HVAC equipment and heat

pumps. To achieve an acceptable indoor environment, space

humidity conditions should be maintained between 30 and

60 percent relative humidity. The probability of microbial

problems, i.e., mold growth, is greatly enhanced at 70 percent

relative humidity and above.

How It Works

The PRO-C Series is a packaged system, which includes

supply and exhaust air fans, outdoor and return air ﬁ lter and

a TEC total energy recovery wheel. The TEC wheel recovers

both sensible (temperature) and latent (moisture) energy; it

cools and dehumidiﬁ es the outdoor air during the cooling

season, while heating and humidifying the outdoor air in the

heating season.

The TEC wheel utilizes a ﬂ uted aluminum substrate,

which is uniformly coated with a fast-acting, adsorbent

desiccant. As the transfer media slowly rotates between the

outdoor and exhaust airstreams, the higher temperature air

gives up its sensible energy to the aluminum. This energy is

then given up to the cooler airstream during the second half

of the revolution. (See Figure 1.)

Just as the temperature is captured and released, so is the

moisture. TEC’s desiccant coating has an enormous internal

surface area and a strong attraction for water vapor. Since the

opposing airstreams have different temperature and moisture

contents, their vapor pressures differ. This difference causes

the transfer of latent energy.

Outdoor Air

(H) 5°F, 4 gr/lb

Supply Air

(H) 54°F, 25 gr/lb

Return Air

(H) 70°F, 32 gr/lb

Exhaust Air

(H) 21°F, 9 gr/lb

Figure 1. An inside view of the PRO-C ventilator with typical

operating conditions during the cooling (C) and heating (H)

season respectively.