Economizer exercise quiz

Question 1

What is an economizer?

Answer 1

uses the cooler temperatures outside to provide cooling

Question 2

Why use an economizer?

Answer 2

free cooling without using compressor

Question 3

what is the code requirement for an HVAC system?

Answer 3

to meet required outdoor air to space

Question 4

what must happen to opperate the economizer?

Answer 4

call for cooling through economizer logic controller

Question 5

what will the conditions have to be in for the compressor to energize?

Answer 5

when outdoor air is above enthalpy set point

Question 6

what temperature mixed air temperature should be maintained and when will the dampers begin to modulate?

Answer 6

55F, when temp goes below 55F damper on economizer will modulate closed and mix with return air to maintain 55F

Question 7

what must be energized to bring the compressor on in economizer mode?

Answer 7

y2 signal to the unit that allows compressor to turn on

Question 8

what is recomended for the economizer to work properly? and why?

Answer 8

minimum 2-stage thermostat to function properly, you need another signal to turn on mechanical cooling to help economizer

Question 9

what is a major cause of economizer problems?

Answer 9

economizer not being properly set up

Question 10

Describe:
1. ExH -

 2. Min Pos - 
3. DCV Max & DVC set -
 4. ABCD Enthalpy setpoint -

Answer 10

1. setting controls at what point power exhaust energizes
2. when terminals receive 24v the dampers will open to minimum position to bring in outside air
3. potentiometers to position dampers in response to an input from the co2 sensors
4. By region and preference is where set point should be. determines what position economizer will allow free cooling

Question 11

when is the exhaust mode used?

Answer 11

with a power exhaust

Question 12

what is the porpose of the time delay in exhaust mode and how long is it?

Answer 12

so exhaust fan does not put building into a negative pressure. About 45 sec

Question 13

what must the thermostat be calling for in order to start the minimum position?

Answer 13

fan switch to “ON” G is energized

Question 14

what is the mixed air temperature formula?

Answer 14

(OAT x OA%) x (RAT x RA%) = MAT

Question 15

what is the MAT if you require 20% fresh air if OAT is 85°F and RA is 71°F?

Answer 15

(85 x 20) x (71 x 80) = 73.8F

Question 16

what is used whith the IAQ setting?

Answer 16

co2 detector

Question 17

where should the answer from 16 be located?

Answer 17

in the space or building

Question 18

when is the freeze protection enabled?

Answer 18

OAT below 45F

Question 19

explain why freeze protection is required when useing an economizer?

Answer 19

if temp drops below 45F, risk of air blowing on water lines could cause freezing

Question 20

what is the relationship between humidity and temperature?

Answer 20

as humidity goes up, temperature goes down

Question 21

what is the porpose of the discharge sensor?

Answer 21

to maintain a 55F discharge or mixed air into the space

Question 22

what are the terminals is the discharge thermostat hooked up to? (Honeywell logic module)

Answer 22

T & T1

Question 23

how do youtest the mixed air/discharge sensor?

Answer 23

attach ohmmeter to 2 wires on sensor and check the chart

Question 24

what is imporyant to check on the enthalpy sensor?

Answer 24

polarity So and S+

Question 25

how many mA should you read if the temperature is 80°F 60% Relative humidity?

Answer 25

slightly over 8ma

Question 26

what tools are required to test the enthalpy sensor?

Answer 26

psychrometer and DC ammeter

Question 27

what two terminals do youmeasure between when testing the enthalpy sensor?

Answer 27

to S on the sensor and the negative lead to either the wire or S on the controller

Question 28

what should be happening if you do not see voltage on terminals TR1 - 4?

Answer 28

outdoor damper should be open and compressor #1 should be running

Question 29

when will you see power at TR & TR1, whats the voltage?

Answer 29

should have 24v anytime the blower is running

Question 30

wher is Y1 connected to on the module and what does it tell the economizer to do?

Answer 30

terminal 1 is Y1 into the module, looks to see if OA is suitable for cooling

Question 31

if T to T1 are open and a jumper accross So to + what shoul you see on a single enthalpy economizer?

Answer 31

LED is on and outside air damper closes to a minimum position

Question 32

if the damper is closeing instead of opening what should you check if useing a belimo motor?

Answer 32

check switch on motor to ensure you have proper rotation

Question 33

during a regular maintenance what should you pay attention to, to prevent a failure of cooling operations?

Answer 33

electrical connections if loose or corroded

Question 34

if the economizer fails, what terminals do you jumper to bring on mechanical cooling?

Answer 34

R and Y2