Address Sore Spots in your Control Specs

08/01/2005


Every facility manager faces two questions when his or her building comes online: 1) Is everything working? and 2) How do I monitor these systems?

From this fundamental starting point, following are examples of key building systems that Broward County, Fla. finds important to monitor and some recommendations as to what this owner would hope engineers address in assembling their controls specifications.

Emergency power

Problem: Is incoming voltage present on all phases? How is it monitored? Is it with a relay on each phase? Is that the cheapest way?

Recommendation: Skip installing the relays, and instead, use our local utility's customer interface for peak shaving with an emergency generator or use a power-monitoring device.

Why? In an emergency, if any phase loses power, some equipment will shut down while some motors continue to run, and this can be damaging to the motor. A building automation system equipped in the above manner, however, can take immediate action to prevent said damage.

Problem: If all phases of power are lost, the equipment in the building will shut down.

Recommendation: UPS backup for the BAS.

Why? When the utility or emergency power returns, the BAS can properly re-sequence start-up, thus preventing equipment damage and spiking kilowatt demand, which results in higher electric bills. The same situation exists when going from generator to utility service, unless the transfer switch is the synchronized type. There is also the situation in which monitoring kilowatts consumed independent of the utility can be used to determine the veracity of the electric bill. Measured independently or obtained via a utility customer interface, this information can be used to activate load-shedding or peak-shaving schemes.

Water supply

Problem: Does a facility have a broken water line or a running toilet? For a building manager it would be nice to be notified if a water pipe in a building breaks, especially during unoccupied times. The same is true for a faucet, water fountain or commode that loses water over a weekend.

Recommendation: Install a flowmeter transducer on each incoming line.

Why? In the event of a broken pipe, a solenoid can be used to shut off the water supply. The exception is fire sprinkler lines that must remain open when fire alarm signals activate.

Furthermore, if externally supplied water is not available, the BAS should be able to notify the designated supply alternate. Water availability can be lost when the facility becomes unprotected by its fire-sprinkler system. Also, if cooling towers are present, the air-conditioning system can be programmed to minimize problems—but only on a temporary basis. Such monitoring capabilities and shut-off solenoids are relatively inexpensive and can save water and money far beyond the initial expense.

Here's some sample language we've developed to address these issues: Water consumed in cooling towers, decorative fountains or pools should be metered separately, as such usage is not subject to sewage disposal fees. This metering needs to be done with a meter approved by the utility supplying the water. Do not connect to the BAS.

General conditions

OK, those are a few examples of specific issues or desires. But what about general conditions? In other words, what specific control points do I desire as an owner?

Outside air. This can be monitored by temperature, humidity and carbon dioxide sensors. Outside air requirements should be related to the number of occupants as prescribed by law. As the number of occupants varies from day to day and hour to hour, it is cost-efficient to vary the amount of outside air that needs to be cooled and filtered to the proper amount. This can be controlled via the use of external and internal carbon dioxide sensors.

The enthalpy of outside air can also be used to reduce costs of air when this parameter is favorable, as compared to return air, which does occur even in southern Florida. Unlike the CO 2 situation noted above, in this case the maximum amount of outside air is desirable. A pressure-relief damper may be needed to prevent the outside doors from closing improperly.

Getting the maximum amount of outside air is also necessary if the building has a smoke control requirement. Virtually eliminating outside-air intake has been necessary when the outside air becomes laden with smoke or noxious odors.

Internal air. Inside air can be classified as discharge—often called supply, which can be confused with outdoor air being "supplied" to the building or its air handlers—space/return/exhaust or mixed air, which is a mixture of return and outside air.

Discharge air parameters must include temperature and analog pressure readings, even for non-VAV systems. Mixed-air temperature readings could be used to help determine the volume of outside air being brought into the building. As it is also necessary to maintain a slight positive pressure inside the building—to minimize untreated air infiltration—it is necessary to monitor this differential pressure parameter.

Interior space air parameters needed are: percentage of relative humidity, CO 2 and temperature. Humidity and return-air temperature sensors should be mounted near but not inside return ducts, because when a fan is off, the readings may no longer be valid. CO 2 sensors can be mounted near or inside the return ducts.

Building lighting. Lighting falls into two major categories: outside and inside. Exterior lights can be for security or aesthetic purposes, and are typically not on 24 hours a day. Security lights that might be on all night should be on different circuits from aesthetic lights that are only on during evening hours. Exterior lights do not need to have any feedback but should be controlled by a photocell that is connected to the BAS. This way, a different schedule can be executed for each application as well as provide the ability to turn on lights during the day for maintenance purposes.

Interior lighting—except for emergency lights—should be controlled by the BAS, based on time of day, or by motion detectors and depending on the specifics of space geometries—or a combination of both. BAS proof of operation is not required. Manual "on" override for all lighting circuits, however, should be provided. Manual "off" should be accomplished via the required circuit breakers.

Heaters. Heaters have two major functions: heat the space during cold weather and provide humidity control year-round. In order to determine when the heaters have been activated, or if they are operating properly, each should have amperage feedback.

Each heater should also have hand-off-automatic (H-O-A) controls. Electric heaters are also used in hot water tanks, but as this use is very limited in office buildings, no BAS connections are needed. This a very different story for hospitals, hotels and restaurants.

Motors. It is important for a building operator to have motor amperage information in order to know if all the motors are running as scheduled and within proper ratings. Small motors that are operated by a wall switch—i.e., "pancake"-type exhaust fans—and whose operation can be easily verified by sound or sight, do not need to have any connections to the BAS. While there are many kinds and sizes of motors, for BAS purposes there are basically two applications in which they are used: constant speed at 60 Hz and variable speed.

Again, here is some sample language we've developed along these lines: Fixed-speed motors that operate 24/7 do not need to have an on/off (binary) connection to the BAS, but all other motors require binary control. All variable-speed motors also need digital control for the variable-speed drive mechanism. Bypass or H-O-A capability is required for all motors.

Building Control Points List

Inputs

Outputs

System Features

General

Analog

Binary

Digital

Analog

Alarms

Programs

Measured

Calc.

1234567891011121314151617

System, Apparatus, Or Area Point Description

Amperage

GPM/Line

Temp/Unit

Humidity

CO2

Pressure

KW

Enthalpy

Drop Out Relays

Pressure

(triangle)P In vs. Out

Shaft Position

Photo Cell

KWH

Start/Stop

Motion Detector

VFD/DDC

Dial Out

Enthalpy

CO2 Control

Temp Control

% RH Control

H-O-A

Electric-Utility Each Leg

O

O

X

O

X

(If) Emergency Generator

X

X

X

X

X

Water-Utility Each Line

X

X

X

X

Outside Air

X

X

X

X

X

X

OA Damper

X

X

2

M

X

X

X

Lights-Outside

X

X

X

Lights-Inside

O

O

X

Motors

X

X

M

X

Duct Heaters

X

X

X

X

X

Discharge Air

X

X

X

Return Air

X

X

X

X

X

Filters

X

HVAC Water

X

X

X

O

O

Water Values

2

M

X

IA Dampers

2

M

X

Space Areas

X

O

X

X

F Air Pumps (+/-)

X

X

Input/Output Summary

X - Required
2 - Required (2 Position Style)
M - Required (Modulating Type)
1 Binary Input From Fire Alarm Panel
O - Optional



Following is a checklist of other monitoring requirements for specific M/E/P equipment:

Fire alarm panels: binary input.

Motors: analog amperage readings.

Fans: pressure readings. Furthermore, all HVAC-related fans need VFD controls. This does not apply to ceiling fans which typically have wall controls.

Pumps: analog pressure differential signal(s) and GPM for each loop. This is not required for fire pumps, jockey pumps, or booster pumps.

Compressors or vacuum units: one analog PSI sensor per unit.

Valves: two-position and modulating. Proper control signals are also required. No feedback information is necessary if analog pressure or GPM readings are available.

Isolation valves: H-O-A and binary control. Confirmed via loop GPM.

AHU chilled-water valves: only an analog output control signal is required as proper operation should be confirmed via discharge air temperatures.

Dampers: two-position and modulating. Need proper control signaling is required for discharge, return, outside air and exhaust.

Discharge and return dampers are two-position (open/shut) and need H-O-A and binary control. Confirmed via duct pressure and motor amperage.

Outside air dampers for IAQ purposes should be modulating and are controlled via CO2 levels with H-O-A type override controls.

Fire dampers: End-switches.

Exhaust dampers for smoke evacuation: binary and H-O-A controls required as are end-switches.

Filters: analog pressure differential readings to indicate condition. In this case, binary signals are not acceptable as a filter may be missing or leaking.

Cooling Towers: Only one Condenser Water Return (CWR) temperature is required but one Condenser Water Supply (CWS) sensor per tower or cell is necessary; water-level detection—magnetic or pressure—is also required per basin as a means of insuring against over or under filing the tower basin(s). Automatic isolation valves per unit are also required if there is more than one tower or cell.

Chillers: Chilled-water supply (CHWS) and return (CHWR) temperatures. Only one CHWR is needed in parallel configurations, but each chiller needs its own CHWS sensor. Automatic isolation valves are required per unit if there is more than one chiller. Each chiller must be able to indicate failure status. "Run" status is not acceptable. Motor amp readings are also mandatory.

Electric domestic hot-water units: Binary and H-O-A relay(s) for kW control where there are large amounts of hot water usage.

Boilers/circulatory units: a shut off solenoid is required if gas or liquid fuel is supplied.

Emergency generator(s): output amperage and transfer switch shaft position required. Binary and H-O-A control to start unit for maintenance or peak shaving and to interrupt fuel flow in the event of fuel spill.



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