NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/energy/6558

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From: Essential Information <[e-mail]>
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Date: 31 Dec 92 13:54 PST
Subject: Re: Energy Ideas - HVAC-2
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NEW TRICKS FOR AN OLD SYSTEM

Many inefficient cooling systems could be improved by proper
maintenance and design. The efficiency and performance of a
heating, ventilating and air conditioning (HVAC) system depends
upon the performance and interaction of each component. The
performance of an efficient HVAC system often degrades when scale
accumulates on heat exchanger surfaces, dirt causes bearings on
motors to stick or changes in the system load increases the
pressure within piping. These problems can be corrected without
the purchase of new equipment.

Types of Cooling Systems

Because of the high heat capacity of water, water-cooled systems
are most commonly used for large-scale applications, i.e. large
buildings and district cooling systems. In these systems, a
cooling unit chills water to about 45o F. The cooling system then
circulates this water throughout a building or a district to
different air-handling systems. These systems take air from
conditioned space and pass it through a heat exchanger, where the
air loses heat to the cool water. The water is then returned to
the central chiller where it is again cooled. Smaller buildings
frequently use individual window air conditioning units.

Improved Efficiency With Proper Maintenance

In an article in the November, 1992 Energy User News ("Georgia
Tech Engineer Outlines HVAC Checklist," p. 4), Doug Moore, the
senior research engineer at Georgia Tech Research Institute,
outlined the steps necessary to maintain the efficiency of HVAC
equipment. For cooling systems, these steps include:

*    Checking the condition and tension of fan belts. A slipping
belt reduces air flow, can cause coil freeze-up and can result in
loss of cooling capacity.

*    Inspecting fan wheels for dirt or obstructions.

*    Cleaning the cooling and heating coils with factory-approved
coil cleaner.

*    Cleaning and inspecting condensate pans and drain piping.

*    Cleaning or replacing air filters (if you have standard
filters, replace them with high efficiency and high capacity
pleated filters).

*    Checking the operation of outside air and relief dampers,
and lubricating as required.

*    Draining and cleaning the cooling tower basin.

*    Cleaning the water distribution basin and clearing nozzles
of obstructions.

*    Checking the water treatment system and chemical level and
adjusting the bleed rate.

*    Checking the fan belts and gear boxes; adjusting or
lubricating them as required.

*    Cleaning pump strainers and verifying proper water flow
rates.

Economizer Installation

The use of equipment such as chillers can be minimized by
providing supplemental cooling with cold air, water or natural
ice during the fall and spring. When the outside air temperature
is sufficiently low and cooling is necessary to offset heat
generated by people, office equipment and lights, air can be
brought in from the outside. Ambient air can "precool" cooling
water, resulting in a lower cooling load for the chillers. Thus,
a smaller chiller can be used during this time of year, or a
chiller connected to an adjustable speed drive (see p. 9) can be
used to match the reduced load. Depending on the location, cool
water or even ice from nearby rivers can be brought to a facility
and used to precool or even completely chill water.

There are two types of economizer controls: dry-bulb control and
enthalpy control. The dry-bulb temperature is perceived
temperature without considering the latent heat of the water
vapor in the air. Dry-bulb control systems compare the outdoor to
indoor dry-bulb temperatures and use precooling when the outdoor
dry-bulb temperature is lower than the indoor dry-bulb
temperature. Enthalpy control systems use an economizer only when
the combined sensible and latent energy level (enthalpy) of
outdoor air is lower than the indoor air.

CASE STUDY:

Economizers at High School Campus
The Phoenix, Arizona Union High School District #210 installed
economizers and control systems in its buildings to permit the
use of outside air for cooling. When the outdoor air temperature
is lower than that of the inside air, the air handling system
precools the indoor air by passing both through a heat exchanger.
(Contact: Kenneth E. Wissinger, Assistant to the Superintendent
for Business and Operations, Phoenix Union High School District
#210, 4502 North Central Avenue, Phoenix, AZ 85012, (602)
271-3301.)

Redesigning the Cooling System

When adding or removing a building or area from a district or
building cooling system, it is important to rescale the cooling
system accordingly. Off-line chillers and cooling towers should
be isolated, and the chilled and condenser water flow rates
correspondingly reduced. Unnecessary pumps should be shut off.
Since many existing cooling systems are oversized, a series of
small pumps or an adjustable speed pump should be installed to
prevent overuse.

CASE STUDIES:

District Cooling Resizing at University
The district cooling system at Yale University in New Haven,
Connecticut was wasting energy to overcome bottlenecks in its
piping system. Undersized pipes and an inefficient chilled water
distribution system increased the pumping pressure in the system
and introduced greater friction losses. The chillers were
modified from two-pass to single-pass units and the piping was
changed throughout the system to reduce friction losses. The
university spent $980,000 to redesign its hydronic loop. The new
design has increased the chiller plant~s output capacity by 2,500
tons and cut fuel bills by $309,000 during a five-month period in
1991, yielding an estimated 1.5 year payback period. In addition,
the increase in the efficiency of the system avoided the
expenditure of $2.5 million for a new chiller. (Contact: Mike
Kieley, Chief Engineer, Sterling Power Plant, 309 Congress
Avenue, New Haven, CT 06510, [phone]).

Pumping Reduction at Airport
The City of Phoenix, Arizona reduced the number of pumps required
to circulate chilled water at the Central Plant for Airport
Terminal 4 by reducing the pressure differential of the secondary
loop from 12 to 5 pounds per square inch (psi). At 12 psi and a
10o F difference between the supply and return water, three 150
horsepower (hp) pumps are required. Lowering the pressure to 5
psi enables one 150 hp adjustable speed drive pump operating at
80 percent capacity to maintain the same 10o F difference.
Savings are estimated at 6,000 kWh and $420 per day. (Contact:
Dimitrios Laloudakis, Energy Conservation Manager, 2631 S. 22nd
Avenue, Phoenix, AZ 85009, [phone].)