Page 207 - Boiler_Operators_Handbook,_Second_Edition

192 Boiler Operator’s Handbook

the register are available and a handy solution to iso- opinion of roof top units because so many of them are
lated problems. Since the register has to draw in room simply constructed to provide air-conditioning at the
air to mix it with the supply air the temperature of the lowest possible first cost. I concur with a number of
room can easily be detected at the register. Movement other engineers that say a typical rooftop unit will last
of the damper in the register is accomplished with a 10 years whereas a typical air handling unit installed
change in position of a bimetallic element in the room indoors will last more than 30 years. Self-contained
air stream. These registers are good for combating vari- refrigeration systems have twice the operating cost of
ations in cooling load in interior spaces where heating systems using chilled water. However the one thing I’ve
isn’t required. They are only a trimming device, capable noted on practically every roof top unit I’ve seen the
of making small corrections in the temperature of the access opening covers are simply pieces of sheet met-
room they’re in. Sometimes they’re a solution for that al along with the casing attached with a minimal num-
lady that’s always cold in the summer. ber of screws and within a year or two are bent, lacking
Almost every design drawing of an air condition- screws, and leaking outside air into the unit disrupting
ing system will show air quantities at each register.
When troubleshooting problems you can use a flow
hood (Figure 5-47) that provides a reading of air flow
through a diffuser or register and into the conditioned
space to compare the existing condition with design.
That will only tell you what the air flow is, and not nec-
essarily give you a reason to start adjusting things like
the damper on the register (if it has one). You can create
more problems in other spaces by adjusting things to
correct a problem in one space. Measure the actual air
flow through a register or diffuser to compare it with the
value on the design drawings and report problems with
airflow that can be attended to by a TAB technician.

RTUs Roof-top Units
RTUs (roof top units) are applied in many com-
mercial applications, schools, small office buildings,
and other applications where the first cost of a facili-
ty is the primary consideration. A unit that combines
all the equipment and pipe and tubing necessary to Figure 5-47. A flow hood
heat or cool spaces in the building are
prefabricated and rigged to the roof of
the building to connect to ducts that
distribute cool and dehumidified or
heated air to the spaces served by that
unit. In addition to steam or hot water
an RTU can be fitted with a natural gas
or oil fired furnace for heating. Typical
RTUs are shown in Figure 5-48.
Roof top units can also be fitted
with a variable speed drive and tem-
perature controls to serve variable air
volume systems as described for AHUs.
I will not go easy on this and tell it
like it is. I detest RTUs. They are a cheap
substitute for a well designed building
and air conditioning system and a pain
in the you-know-where. I have a low
Figure 5-48. RTUs