Commercial Architecture March 2018 - 48

PROJECT

hvac

Important Requirements For IAQ

refrigerant (VFR) technology common with some larger
systems. That limitation, however, is about to change.
MOLD & MILDEW

15%

MICRO-COMPRESSORS

To eliminate the problem of unconditioned, raw, humid
outside air entering guestrooms through the fresh-air
door, some PTAC manufacturers have offered a solution:

TEMPERATURE

dropping in an independent, miniature 6- x 4-in. precon-

35%

FRESH AIR

15%

ditioning coil module. Just about the size of a soup can,
this micro-compressor sits on top of the primary system
by the fresh-air door in the dead space of the PTAC unit.
When the humidistat level reaches about 60%, the micro-compressor kicks on and dehumidifies incoming air.
However, several engineers expressed concern over

HUMIDITY

NOISE

10%

25%

the efficacy of such micro-compressors-doubting, for
example, whether the PTAC miniature drop-in air conditioner module can bring a humid 35 cfm (cubic feet/
min.) at 95 F to 72 F while also wringing out enough hu-

When hotel engineers were asked to identify the most important requirements for indoor-air-quality systems, temperature and noise
were the top factors.

midity to make that space neutral. While the fresh air
"exhaust" fans on these systems are rated at 35 cfm, the
airflow may be hampered as it travels around various obstructions, which results in increased resistance to flow

don't want the bed sheets to feel damp."

by manufacturers to specifically target the hospitality

Beyond humidity control, energy efficiency is espe-

market-because of their lower initial cost.

and effectively cuts the cfm in half.
"With hot, humid air pouring into a building," Mar-

cially desirable in markets where potential government

To introduce outside air into the guestroom, PTAC

riott's Terry Smith explained, "I must be sure that the

tax rebates or power utility rebates are available. Howev-

units have traditionally incorporated a tiny lever, or

dehumidification section can react fast enough to keep

er, just as important as efficiency is guest experience, in-

fresh-air door. However, the air in these systems is neither

the incoming airstream at roughly room neutral-70

cluding the noise level and aesthetics of the PTAC unit.

measured nor conditioned. Rather, it's simply raw, hot,

F/50% RH."

"Give me a $400 PTAC that's extremely noisy and

humid outside air, which forces the PTAC units to work

Lastly, as with any mechanical system, adding more

I've lost," said Marriott's John Seipp. (Most PTAC chassis

harder and worsens indoor comfort levels by introducing

moving parts may also increase maintenance costs, ener-

are in the $600 range).

unconditioned air into the indoor loop.

gy load, and noise level.

Despite the problems that unconditioned air can in-

"I think the micro-compressor is a great idea. It is a

MAXIMIZING COMFORT AND HEALTH

troduce, for many hotel chains, the benefits of PTAC

cost-effective solution," said John Seipp, "however, it

Fresh air is needed to reduce humidity, toxins, and patho-

units far outweigh the disadvantages, especially with re-

probably is going to be noisier for the size and adds an

gens inside hotel guestrooms.

cent innovations for introducing makeup air.

additional energy load."

"The more ventilation you provide, the lower the con-

Typically, PTAC systems are attractive, 42-in.-wide,

centration of whatever contaminants there might be,"

self-contained, all-in-one package wall units with plastic

VARIABLE-SPEED INVERTERS

said Roger Hedrick, principal engineer with NORESCO,

fronts and installed below a window in order to discharge

One significant development in energy efficiency for

Westborough, MA (noresco.com).

directly into the guestroom. These are combination air

the next generation of PTAC units will be the intro-

conditioners designed to provide the heating and cooling

duction of advanced variable-speed inverter technology.

for individual guestrooms.

Compared to a traditional constant-speed PTAC unit, a

Toxic chemicals include carbon monoxide, radon,
volatile organic compounds (VOCs), elemental particles,
smoke, and manmade fibers, and they can show up ev-

Select-service hotels use PTACs as an alternative to

variable-capacity inverter reaches a set point faster and

erywhere from furniture and carpet backing to rooms

hard ducting outside air into all the guestrooms, where

maintains precise temperatures with minimal energy use.

heavily sprayed with pesticides.

ceiling space in the corridor may limit the room for

Living pathogens-found naturally in the environ-

ductwork.
"Generally, the select-service hotels are relying on the

consumption than a variable-speed system. Unlike vari-

outside air coming through the PTAC," explained Marri-

able-speed technology, constant-speed units create wide

ott's Smith.

temperature swings, because when the unit is off, it is not

ment-include molds, mildew, dust mites, spores, pollens,
bacteria, microbes, and viruses.
"Fungus and molds go hand-in-hand with ventilation

Constant-speed PTAC units run at full capacity and
then shut off. This stop-start cycle results in higher power

dehumidifying or cooling until it starts up again.

and humidity control," said Lew Harriman of Ma-

Some PTAC manufacturers have lowered the carbon

son-Grant. Buildings are now constructed to comply

footprint of their units by using a more efficient refriger-

In variable-speed systems, on the other hand, the in-

with tighter standards than in years past. While the air-

ant with a lower global warming potential (GWP), such

verter varies the speed of the compressor motor to contin-

tight infrastructure offers superior insulation and energy

as the refrigerant, R-32.

uously regulate the temperature. At initial start-up, the

efficiency, it can also lead to a lack of fresh air indoors.

PTACs are also a more economical solution with the

unit reaches a designated set temperature and then reduc-

advantages of low cost, easy installation, and simple

es capacity as the set temperature is achieved by slowing

HAZARDS OF UNCONDITIONED AIR

maintenance. One disadvantage, however, is that PTACs

the compressor speed, which in turn drops the refrigerant

Select-service hotels often specify PTAC units-designed

don't use the more efficient inverter-driven, variable-flow

flow rate. The compressor never shuts off completely. The

COMMERCI A L A RCHI T EC T URE

MARCH 2018

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