ENERGY MANAGEMENT HANDBOOKS phần 4 pptx

HVAC SYSTEMS 265

building service personnel. For example the controls on

a unit ventilator include a room temperature thermostat

which controls the valve on the heating or cooling coil,

a damper control which adjusts the proportion of fresh

air mixed with recirculated room air, and a low-limit

thermostat which prevents the temperature of outside

air from dropping below a preset temperature (usually

55 to 60°F; 13 to 16°C). A common error of occupants or

building custodians in response to a sense that the air

supplied by the unit ventilator is too cold is to increase

the setpoint on the low-limit thermostat, which prevents

free cooling from outside air or, on systems without a

cooling coil, prevents cooling altogether. Controls which

are subject to misadjustment by building occupants

should be placed so that they cannot be tampered

with.

The energy consumption of thermally heavy

buildings is less related to either the inside or outside

air temperature. Both the heating and cooling loads in

thermally heavy buildings are heavily dependent on

the heat generated from internal loads and the thermal

energy stored in the building mass which may be dis￾Figure 10.13 Wet-side economizer schematic diagram.

266 ENERGY MANAGEMENT HANDBOOK

sipated at a later time.

In an indirect control system the amount of energy

consumed is not a function of human thermal comfort

needs, but of other factors such as outdoor tempera￾ture, humidity, or enthalpy. Indirect control systems

determine the set points for cool air temperature, water

temperatures, etc. As a result indirect control systems

tend to adjust themselves for peak conditions rather

than actual conditions. This leads to overheating or

overcooling of spaces with less than peak loads.

One of the most serious threats to the effi ciency

of any system is the need to heat and cool air or water

simultaneously in order to achieve the thermal balance

required for adequate conditioning of spaces. Figure

10.14 indicates that 20 percent of the energy consumed

in a commercial building might be used to reheat cooled

air, offsetting another 6 percent that was used to cool the

air which was later reheated. For the example building

the energy used to cool reheated air approaches that

actually used for space cooling.

Following the 1973 oil embargo federal guidelines

encouraged everyone to reduce thermostat settings to

68°F (20°C) in winter and to increase thermostat settings

in air-conditioned buildings to 78°F (26°C) in summer.

[In 1979, the winter guideline was reduced farther to

65°F (18°C).] The effect of raising the air-conditioning

thermostat on a reheat, dual-duct, or multizone system

is actually to increase energy consumption by increas￾ing the energy required to reheat air which has been

mechanically cooled (typically to 55°F; 13°C).

To minimize energy consumption on these types

of systems it makes more sense to raise the discharge

temperature for the cold-deck to that required to cool pe￾rimeter areas to 78°F (26°C) under peak conditions. If the

system was designed to cool to 75°F (24°C) on a peak day

using 55°F (13°C) air, the cold deck discharge could be

increased to 58°F (14.5°C) to maintain space temperatures

at no more than 78°F (26°C), saving about $5 per cfm

per year. Under less-than-peak conditions these systems

would operate more effi ciently if room temperatures were

allowed to fall below 78°F (26°C) than to utilize reheated

air to maintain this temperature.

More extensive discussion of energy management

control systems may be found in Chapters 12 and 22.

10.5.7 HVAC Equipment

The elements which provide heating and cooling

to a building can be categorized by their intended func￾tion. HVAC equipment is typically classifi ed as heating

equipment, including boilers, furnaces and unit heaters;

cooling equipment, including chillers, cooling towers

and air-conditioning equipment; and air distribution

elements, primarily air-handling units (AHUs) and fans.

A more lengthy discussion of boilers may be found

in Chapter 6, followed by a discussion of steam and

condensate systems in Chapter 7. Cooling equipment is

discussed in section 10.6, below. What follows here re￾lates mostly to air-handling equipment and distribution

systems.

Figure 10.14 depicts the typical energy cost dis￾tribution for a large commercial building which em￾ploys an all-air reheat-type HVAC system. Excluding

the energy costs associated with lighting, kitchen and

miscellaneous loads which are typically 25-30 percent

of the total, the remaining energy can be divided into

two major categories: the energy associated with heat￾ing and cooling and the energy consumed in distribu￾tion. The total energy consumed for HVAC systems

is therefore dependent on the effi ciency of individual

components, the effi ciency of distribution and the ability

of the control system to accurately regulate the energy

consuming components of the system so that energy is

not wasted.

The size (and heating, cooling, or air-moving ca￾pacity) of HVAC equipment is determined by the me￾chanical designer based upon a calculation of the peak

internal and envelope loads. Since the peak conditions

are arbitrary (albeit well-considered and statistically

valid) and it is likely that peak loads will not occur

simultaneously throughout a large building or complex

Figure 10.14 Energy cost distribution for a typical

non-residential building using an all-air reheat HVAC

system.

Space

cooling

Other

uncertain)

(magnitude

Kitchen

& process

Domestic

hot water

Cooling of reheat

Pumps

Fans

Lighting

Reheat

Space heating

HVAC SYSTEMS 267

requiring all equipment to operate at its rated capacity,

it is common to specify equipment which has a total

capacity slightly less than the peak requirement. This

diversity factor varies with the function of the space.

For example, a hospital or classroom building will use

a higher diversity multiplier than an offi ce building.

In sizing heating equipment however, it is not un￾common to provide a total heating capacity from several

units which exceeds the design heating load by as much

as fi fty percent. In this way it is assured that the heating

load can be met at any time, even in the event that one

unit fails to operate or is under repair.

The selection of several boilers, chillers, or air￾handling units whose capacities combine to provide

the required heating and cooling capability instead of

single large units allows one or more components of

the system to be cycled off when loads are less than the

maximum.

This technique also allows off-hours use of specifi c

spaces without conditioning an entire building.

Equipment Effi ciency

Effi ciency, by defi nition, is the ratio of the energy

output of a piece of equipment to its energy input, in

like units to produce a dimensionless ratio. Since no

equipment known can produce energy, effi ciency will

always be a value less than 1.0 (100%).

Heating equipment which utilizes electric resis￾tance appears at first glance to come closest to the

ideal of 100 percent effi ciency. In fact, every kilowatt of

electrical power consumed in a building is ultimately

converted to 3413 Btu per hour of heat energy. Since this

is a valid unit conversion it can be said that electric re￾sistance heating is 100 percent effi cient. What is missing

from the analysis however, is the ineffi ciency of produc￾ing electricity, which is most commonly generated using

heat energy as a primary energy source.

Electricity generation from heat is typically about

30 percent effi cient, meaning that only 30 percent of the

heat energy is converted into electricity, the rest being

dissipated as heat into the environment. Energy con￾sumed as part of the generation process and energy lost

in distribution use up about ten percent of this, leaving

only 27 percent of the original energy available for use

by the consumer. By comparison, state-of-the-art heating

equipment which utilizes natural gas as a fuel is more

than eighty percent effi cient. Distribution losses in natu￾ral gas pipelines account for another 5 percent, making

natural gas approximately three times as effi cient as a

heat energy source than electricity.

The relative efficiency of cooling equipment is

usually expressed as a coeffi cient of performance (COP),

which is defi ned as the ratio of the heat energy extracted

to the mechanical energy input in like units. Since the

heat energy extracted by modem air conditioning far

exceeds the mechanical energy input a COP of up to 6

is possible.

Air-conditioning equipment is also commonly

rated by its energy effi ciency ratio (EER) or seasonal en￾ergy effi ciency ratio (SEER). EER is defi ned as the ratio

of heat energy extracted (in Btu/hr) to the mechanical

energy input in watts. Although it should have dimen￾sions of Btu/hr/watt, it is expressed as a dimensionless

ratio and is therefore related to COP by the equation

EER = 3.41 • COP (10.4)

Although neither COP nor EER is the effi ciency

of a chiller or air-conditioner, both are measures which

allow the comparison of similar units. The term air-con￾ditioning effi ciency is commonly understood to indicate

the extent to which a given air-conditioner performs to

its maximum capacity. As discussed below, most equip￾ment does not operate at its peak effi ciency all of the

time. For this reason, the seasonal energy effi ciency ratio

(SEER), which takes varying effi ciency at partial load

into account, is a more accurate measure of air-condi￾tioning effi ciency than COP or EER.

In general, equipment effi ciency is a function of

size. Large equipment has a higher effi ciency than small

equipment of similar design. But the rated effi ciency of

this equipment does not tell the whole story. Equipment

effi ciency varies with the load imposed. All equipment

operates at its optimum effi ciency when operated at or

near its design full-load condition. Both overloading

and under-loading of equipment reduces equipment ef￾fi ciency.

This fact has its greatest impact on system effi cien￾cy when large systems are designed to air-condition an

entire building or a large segment of a major complex.

Since air-conditioning loads vary and since the design

heating and cooling loads occur only rarely under the

most severe weather or occupancy conditions, most of

the time the system must operate under-loaded. When

selected parts of a building are utilized for off-hours

operation this requires that the entire building be condi￾tioned or that the system operate far from its optimum

conditions and thus at far less than its optimum effi -

ciency.

Since most heating and cooling equipment oper￾ates at less than its full rated load during most of the

year, its part-load effi ciency is of great concern. Because

of this, most state-of-the-art equipment operates much

closer to its full-load effi ciency than does older equip-

268 ENERGY MANAGEMENT HANDBOOK

ment. A knowledge of the actual operating effi ciency of

existing equipment is important in recognizing econom￾ic opportunities to reduce energy consumption through

equipment replacement.

Distribution Energy

Distribution energy is most commonly electrical

energy consumed to operate fans and pumps, with fan

energy typically being far greater than pump energy ex￾cept in all-water distribution systems. The performance

of similar fans is related by three fan laws which relate

fan power, airfl ow, pressure and effi ciency to fan size,

speed and air density. The reader is referred to the

ASHRAE Handbook: HVAC Systems and Equipment for

additional information on fans and the application of

the fan laws.3

Fan energy is a function of the quantity of airfl ow

moved by the fan, the distance over which it is moved,

and the velocity of the moving air (which infl uences

the pressure required of the fan). Most HVAC systems,

whether central or distributed packaged systems, all￾air, all-water, or a combination are typically oversized

for the thermal loads that actually occur. Thus the fan

is constantly required to move more air than necessary,

creating inherent system ineffi ciency.

One application of the third fan law describes

the relationship between fan horsepower (energy con￾sumed) and the airfl ow produced by the fan:

W1 = W2 × (Q1/Q2)3 (10.5)

where

W = fan power required, hp

Q = volumetric fl ow rate, cfm

Because fan horsepower is proportional to the cube

of airfl ow, reducing airfl ow to 75 percent of existing

will result in a reduction in the fan horsepower by the

cube of 75 percent, or about 42 percent: [(0.75)3 = 0.422]

Even small increases in airfl ow result in disproportional

increases in fan energy. A ten percent increase in airfl ow

requires 33 percent more horsepower [1.103 = 1.33],

which suggests that airfl ow supplied solely for ventila￾tion purposes should be kept to a minimum.

All-air systems which must move air over great

distances likewise require disproportionate increases in

energy as the second fan law defi nes the relationship

between fan horsepower [W] and pressure [p], which

may be considered roughly proportional to the length

of ducts connected to the fan:

W1 = W2 × (P1/P1)3/2 (10.6)

The use of supply air at temperatures of less than

55°F (13°C) for primary cooling air permits the use of

smaller ducts and fans, reducing space requirements

at the same time. This technique requires a complex

analysis to determine the economic benefi t and is sel￾dom advantageous unless there is an economic benefi t

associated with space savings.

System Modifi cations

In examining HVAC systems for energy conser￾vation opportunities, the less effi cient a system is, the

greater is the potential for signifi cant conservation to

be achieved. There are therefore several “off-the-shelf”

opportunities for improving the energy efficiency of

selected systems.

All-air Systems—Virtually every type of all-air

system can benefi t from the addition of an economizer

cycle, particularly one with enthalpy controls. Systems

with substantial outside air requirements can also ben￾efi t from heat recovery systems which exchange heat

between exhaust air and incoming fresh air. This is a

practical retrofi t only when the inlet and exhaust ducts

are in close proximity to one another.

Single zone systems, which cannot provide suf￾ficient control for varying environmental conditions

within the area served can be converted to variable air

volume (VAV) systems by adding a VAV terminal and

thermostat for each new zone. In addition to improving

thermal comfort this will normally produce a substantial

saving in energy costs.

VAV systems which utilize fans with inlet vanes

to regulate the amount of air supplied can benefi t from

a change to variable speed or variable frequency fan

drives. Fan effi ciency drops off rapidly when inlet vanes

are used to reduce airfl ow.

In terminal reheat systems, all air is cooled to

the lowest temperature required to overcome the peak

cooling load. Modern “discriminating” control systems

which compare the temperature requirements in each

zone and cool the main airstream only to the tempera￾ture required by the zone with the greatest requirements

will reduce the energy consumed by these systems.

Reheat systems can also be converted to VAV systems

which moderate supply air volume instead of supply air

temperature, although this is a more expensive altera￾tion than changing controls.

Similarly, dual-duct and multizone systems can ben￾efi t from “smart” controls which reduce cooling require￾ments by increasing supply air temperatures. Hot-deck

temperature settings can be controlled so that the tem￾perature of warm supply air is just high enough to meet

HVAC SYSTEMS 269

design heating requirements with 100 percent hot-deck

supply air and adjusted down for all other conditions

until the hot-deck temperature is at room temperature

when outside temperatures exceed 75°F (24°C). Dual duct

terminal units can be modifi ed for VAV operation.

An economizer option for multizone systems is

the addition of a third “bypass” deck to the multizone

air-handling unit. This is not appropriate as a retrofi t

although an economizer can be utilized to provide cold￾deck air as a retrofi t.

All-water systems—Wet-side economizers are the

most attractive common energy conservation measure

appropriate to chilled water systems. Hot-water systems

benefi t most from the installation of self-contained ther￾mostat valves, to create heating zones in spaces formerly

operated as single-zone heating systems.

Air-water Induction—Induction systems are sel￾dom installed anymore but many still exist in older

buildings. The energy-effi ciency of induction systems

can be improved by the substitution of fan-powered

VAV terminals to replace the induction terminals.

10.6 COOLING EQUIPMENT

The most common process for producing cooling

is vapor-compression refrigeration, which essentially

moves heat from a controlled environment to a warmer,

uncontrolled environment through the evaporation of

a refrigerant which is driven through the refrigeration

cycle by a compressor.

Vapor compression refrigeration machines are

typically classified according to the method of op￾eration of the compressor. Small air-to-air units most

commonly employ a reciprocating or scroll compres￾sor, combined with an air-cooled condenser to form

a condensing unit. This is used in conjunction with a

direct-expansion (DX) evaporator coil placed within

the air-handling unit.

Cooling systems for large non-residential buildings

typically employ chilled water as the medium which

transfers heat from occupied spaces to the outdoors

through the use of chillers and cooling towers.

10.6.1 Chillers

The most common type of water chiller for large

buildings is the centrifugal chiller which employs a

centrifugal compressor to compress the refrigerant,

which extracts heat from a closed loop of water which is

pumped through coils in air-handling or terminal units

within the building. Heat is rejected from the condenser

into a second water loop and ultimately rejected to the

environment by a cooling tower.

The operating fl uid used in these chillers may be

either a CFC or HCFC type refrigerant. Many existing

centrifugal chillers use CFC-11 refrigerants, the manu￾facture and use of which is being eliminated under the

terms of the Montreal Protocol. New refrigerants HCFC￾123 and HCFC-134a are being used to replace the CFC

refrigerants but refrigerant modifications to existing

equipment will reduce the overall capacity of this equip￾ment by 15 to 25 percent.

Centrifugal chillers can be driven by open or

hermetic electric motors or by internal combustion

Table 10.1 Summary of HVAC System Modifi cations for Energy Conservation

System type Energy Conservation Opportunities

All-air systems (general): economizer

heat recovery

Single zone systems conversion to VAV

Variable air volume (VAV) systems replace fan inlet vane control with variable frequency drive fan

Reheat systems use of discriminating control systems

conversion to VAV

Constant volume dual-duct systems use of discriminating control systems

conversion to dual duct VAV

Multizone systems use of discriminating control systems

addition of by-pass deck*

All-water systems:

hydronic heating systems addition of thermostatic valves

chilled water systems wet-side economizer

Air-water induction systems replacement with fan-powered VAV terminals

*Requires replacement of air-handling unit

270 ENERGY MANAGEMENT HANDBOOK

engines or even by steam or gas turbines. Natural gas

engine-driven equipment sized from 50 to 800 tons of

refrigeration are available and in some cases are used to

replace older CFC-refrigerant centrifugal chillers. These

engine-driven chillers are viable when natural gas costs

are suffi ciently low. Part-load performance modulates

both engine speed and compressor speed to match the

load profi le, mainta ining close to the peak effi ciency

down to 50 percent of rated load. They can also use heat

recovery options to take advantage of the engine jacket

and exhaust heat.

Turbine-driven compressors are typically used on

very large equipment with capacities of 1200 tons or

more. The turbine may be used as part of a cogeneration

process but this is not required. (For a detailed discus￾sion of cogeneration, see Chapter 7.) If excess steam is

available, in industry or a large hospital, a steam turbine

can be used to drive the chiller. However the higher load

on the cooling tower due to the turbine condenser must

be considered in the economic analysis.

Small water chillers, up to about 200 tons of capac￾ity, may utilize reciprocating or screw compressors and

are typically air-cooled instead of using cooling towers.

An air-cooled chiller uses a single or multiple compres￾sors to operate a DX liquid cooler. Air-cooled chillers are

widely used in commercial and large-scale residential

buildings.

Other types of refrigeration systems include liquid

overfeed systems, fl ooded coil systems and multi-stage

systems. These systems are generally used in large indus￾trial or low-temperature applications.

10.6.2 Absorption Chillers

An alternative to vapor-compression refrigeration

is absorption refrigeration which uses heat energy to

drive a refrigerant cycle, extracting heat from a con￾trolled environment and rejecting it to the environment

(Figure 10.15). Thirty years ago absorption refrigeration

was known for its low coeffi cient of performance and

high maintenance requirements. Absorption chillers

used more energy than centrifugal chillers and were

economical only if driven by a source of waste heat.

Today, due primarily to the restriction on the use

of CFC and HCFC refrigerants, the absorption chiller

is making a comeback. Although new and improved, it

still uses heat energy to drive the refrigerant cycle and

typically uses aqueous lithium bromide to absorb the

refrigerant and water vapor in order to provide a higher

coeffi cient of performance.

The new absorption chillers can use steam as a

heat source or be direct-fi red. They can provide simul￾taneous heating and cooling which eliminates the need

for a boiler. They do not use CFC or HCFC refrigerants,

which may make them even more attractive in years

to come. Improved safety and controls and better COP

(even at part load) have propelled absorption refrigera￾tion back into the market.

In some cases, the most effective use of refrig￾eration equipment in a large central-plant scenario is

to have some of each type, comprising a hybrid plant.

From a mixture of centrifugal and absorption equip￾ment the operator can determine what equipment will

provide the lowest operating cost under different con￾Figure 10.15 Simplifi ed absorption cycle schematic diagram.

HVAC SYSTEMS 271

ditions. For example a hospital that utilizes steam year

round, but at reduced rates during summer, might use

the excess steam to run an absorption chiller or steam￾driven turbine centrifugal chiller to reduce its summer￾time electrical demand charges.

10.6.3 Chiller Performance

Most chillers are designed for peak load and then

operate at loads less than the peak most of the time.

Many chiller manufacturers provide data that identifi es

a chiller’s part-load performance as an aid to evaluat￾ing energy costs. Ideally a chiller operates at a desired

temperature difference (typically 45-55 degrees F; 25-30

degrees C) at a given fl ow rate to meet a given load.

As the load requirement increases or decreases, the

chiller will load or unload to meet the need. A reset

schedule that allows the chilled water temperature to

be adjusted to meet thermal building loads based on

enthalpy provides an ideal method of reducing energy

consumption.

Chillers should not be operated at less than 50 per￾cent of rated load if at all possible. This eliminates both

surging and the need for hot-gas bypass as well as the

potential that the chiller would operate at low effi ciency.

If there is a regular need to operate a large chiller at less

than one-half of the rated load it is economical to install

a small chiller to accommodate this load.

10.6.4 Thermal Storage

Thermal storage can be another effective way of

controlling electrical demand by using stored chilled

water or ice to offset peak loads during the peak de￾mand time. A good knowledge of the utility consump￾tion and/or load profi le is essential in determining the

applicability of thermal storage. See Chapter 19 for a

discussion of thermal storage systems.

10.6.5 Cooling Towers

Cooling towers use atmospheric air to cool the

water from a condenser or coil through evaporation. In

general there are three types of cooling tower, named for

the relationship between the fan-powered airfl ow and the

fl ow of water in the tower: counterfl ow induced draft,

crossfl ow induced draft and counterfl ow forced draft.

The use of variable-speed, two-speed or three-speed

fans is one way to optimize the control of the cooling

tower in order to reduce power consumption and provide

adequate water cooling capacity. As the required cooling

capacity increases or decreases the fans can be sequenced

to maintain the approach temperature difference. For

most air-conditioning systems this usually varies between

5 and 12 degrees F (3 to 7 degrees C).

When operated in the winter, the quantity of air

must be carefully controlled to the point where the

water spray is not allowed to freeze. In cold climates it

may be necessary to provide a heating element within

the tower to prevent freeze-ups. Although electric resis￾tance heaters can be used for this purpose it is far more

effi cient to utilize hot water or steam as a heat source if

available.

10.6.6 Wet-side Economizer

The use of “free-cooling” using the cooling tower

water to cool supply air or chilled water is referred to

as a wet-side economizer. The most common and effec￾tive way of interconnecting the cooling tower water to

the chilled water loop is through the use of a plate-and￾frame heat exchanger which offers a high heat transfer

rate and low pressure drop. This method isolates the

cooling tower water from the chilled water circuit main￾taining the integrity of the closed chilled water loop.

Another method is to use a separate circuit and pump

that allows cooling tower w ater to be circulated through

a coil located within an air-handling unit.

The introduction of cooling tower water, into

the chilled water system, through a so-called strainer

cycle, can create maintenance nightmares and should

be avoided. The water treatment program required for

chilled water is intensive due to the required cleanness

of the water in the chilled water loop.

10.6.7 Water treatment

A good water treatment program is essential to

the maintenance of an effi cient chilled water system.

Filtering the cooling tower water should be evaluated.

In some cases, depending on water quality, this can save

the user a great deal of money in chemicals. Pretreating

new system s prior to initial start-up will also provide

longer equipment life and insure proper system perfor￾mance.

Chiller performance is based on given design pa￾rameters and listed in literature provided by the chiller

manufacturer. The performance will vary with building

load, chilled water temperature, condenser water tem￾perature and fouling factor. The fouling factor is the re￾sistance caused by dirt, scale, silt, rust and other deposits

on the surface of the tubes in the chiller and signifi cantly

affects the overall heat transfer of the chiller.

10.7 DOMESTIC HOT WATER

The creation of domestic hot water (DHW) repre￾sents about 4 percent of the annual energy consumption

272 ENERGY MANAGEMENT HANDBOOK

in typical non-residential buildings. In buildings where

sleeping or food preparation occur, including hotels,

restaurants, and hospitals, DHW may account for as

much as thirty percent of total energy consumption.

Some older lavatory faucets provide a fl ow of 4 to 6

gal/min (0.25 to 0.38 l/s). Since hand washing is a func￾tion more of time than water use, substantial savings can

be achieved by reducing water fl ow. Reduced-fl ow fau￾cets which produce an adequate spray pattern can reduce

water consumption to less than 1 gal/min (0.06 l/s). Flow

reducing aerator replacements are also available.

Reducing DHW temperature has also been shown

to save energy in non-residential buildings. Since most

building users accept water at the available tempera￾ture, regardless of what it is, water temperature can be

reduced from the prevailing standard of 140°F (60°C)

to a 105°F (40°C) utilization temperature saving up to

one-half of the energy used to heat the water.

Many large non-commercial buildings employ re￾circulating DHW distribution systems in order to reduce

or eliminate the time required and water wasted in

fl ushing cold water from hot water piping. Recirculating

distribution is economically attractive only where DHW

use is high and/or the cost of water greatly exceeds the

cost of water heating. In most cases the energy required

to keep water in recirculating DHW systems hot exceeds

the energy used to heat the water actually used.

To overcome this waste of energy there is a trend

to convert recirculating DHW systems to localized point￾of-use hot water heating, particularly in buildings where

plumbing facilities are widely separated. In either case

insulation of DHW piping is essential in reducing the

waste of energy in distribution. One-inch of insulation

on DHW pipes will result in a 50% reduction in the

distribution heat loss.

One often-overlooked energy conservation oppor￾tunity associated with DHW is the use of solar-heated

hot water. Unlike space-heating, the need for DHW is

relatively constant throughout the year and peaks dur￾ing hours of sunshine in non-residential buildings. Year￾round use amortizes the cost of initial equipment faster

than other active-solar options.

Many of the techniques appropriate for reducing

energy waste in DHW systems are also appropriate for

energy consumption in heated service water systems for

industrial buildings or laboratories.

10.8 ESTIMATING HVAC

ENERGY CONSUMPTION

The methods for estimating building heating and

cooling loads and the consumption of energy by HVAC

systems are described in Chapter 9.

References

1. ASHRAE Handbook: Fundamentals, American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc., Atlanta,

1993.

2. ASHRAE Handbook: HVAC Applications, American Society of Heat￾ing, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta,

1995.

3. ASHRAE Handbook: HVAC Systems and Equipment, American So￾ciety of Heating, Refrigerating and Air-Conditioning Engineers,

Inc., Atlanta, 1992.

4. ASHRAE Handbook: Refrigeration, American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc., Atlanta,

1 9 9 4 .

K.K. LOBODOVSKY

BSEE & BSME

Certifi ed Energy Auditor

State of California

11.1 INTRODUCTION

Effi cient use of electric energy enables commercial,

industrial and institutional facilities to minimize operat￾ing costs, and increase profi ts to stay competitive.

The majority of electrical energy in the United

States is used to run electric motor driven systems.

Generally, systems consist of several components, the

electrical power supply, the electric motor, the motor

control, and a mechanical transmission system.

There are several ways to improve the systems'

effi ciency. The cost effective way is to check each com￾ponent of the system for an opportunity to reduce elec￾trical losses. A qualifi ed individual should oversee the

electrical system since poor power distribution within a

facility is a common cause of energy losses.

Technology Update Ch. 181 lists 20 items to help

facility management staff identify opportunities to im￾prove drive system effi ciency.

1. Maintain Voltage Levels.

2. Minimize Phase Imbalance.

3. Maintain Power Factor.

4. Maintain Good Power Quality.

5. Select Effi cient Transformers.

6. Identify and Fix Distribution System Losses.

7. Minimize Distribution System Resistance.

8. Use Adjustable Speed Drives (ASDs) or 2-Speed

Motors Where Appropriate.

9. Consider Load Shedding.

10. Choose Replacement Before a Motor Fails.

11. Choose Energy-Effi cient Motors.

12. Match Motor Operating Speeds.

13. Size Motors for Effi ciency.

14. Choose 200 Volt Motors for 208 Volt Electrical Sys￾tems.

15. Minimize Rewind Losses.

16. Optimize Transmission Effi ciency.

17. Perform Periodic Checks.

18. Control Temperatures.

19. Lubricate Correctly.

20. Maintain Motor Records.

Some of these steps require the one-time involve￾ment of an electrical engineer or technician. Some

steps can be implemented when motors fail or major

capital changes are made in the facility. Others involve

development of a motor monitoring and maintenance

program.

11.2 POWER SUPPLY

Much of this information consists of standards

defi ned by the National Electrical Manufacturers As￾sociation (NEMA).

The power supply is one of the major factors affect￾ing selection, installation, operation, and maintenance

of an electrical motor driven system. Usual service con￾ditions, defi ned in NEMA Standard Publication MG1,

Motors and Generators,

2 include:

• Motors designed for rated voltage, frequency, and

number of phases.

• The supply voltage must be known to select the

proper motor.

• Motor nameplate voltage will normally be less

then nominal power system voltage.

Nominal Motor Utilization

Power System (Nameplate) Voltage

Voltage (Volts) Volts ——————— ——————————

208 200

240 230

480 460

600 575

2400 2300

4160 4000

6900 6600

13800 13200

• Operation within tolerance of ±10 percent of the

rated voltage.

CHAPTER 11

ELECTRIC ENERGY MANAGEMENT

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