Economizer exercise quiz Flashcards
What is an economizer?
uses the cooler temperatures outside to provide cooling
Why use an economizer?
free cooling without using compressor
what is the code requirement for an HVAC system?
to meet required outdoor air to space
what must happen to opperate the economizer?
call for cooling through economizer logic controller
what will the conditions have to be in for the compressor to energize?
when outdoor air is above enthalpy set point
what temperature mixed air temperature should be maintained and when will the dampers begin to modulate?
55F, when temp goes below 55F damper on economizer will modulate closed and mix with return air to maintain 55F
what must be energized to bring the compressor on in economizer mode?
y2 signal to the unit that allows compressor to turn on
what is recomended for the economizer to work properly? and why?
minimum 2-stage thermostat to function properly, you need another signal to turn on mechanical cooling to help economizer
what is a major cause of economizer problems?
economizer not being properly set up
Describe:
1. ExH -
2. Min Pos - 3. DCV Max & DVC set - 4. ABCD Enthalpy setpoint -
- setting controls at what point power exhaust energizes
- when terminals receive 24v the dampers will open to minimum position to bring in outside air
- potentiometers to position dampers in response to an input from the co2 sensors
- By region and preference is where set point should be. determines what position economizer will allow free cooling
when is the exhaust mode used?
with a power exhaust
what is the porpose of the time delay in exhaust mode and how long is it?
so exhaust fan does not put building into a negative pressure. About 45 sec
what must the thermostat be calling for in order to start the minimum position?
fan switch to “ON” G is energized
what is the mixed air temperature formula?
(OAT x OA%) x (RAT x RA%) = MAT
what is the MAT if you require 20% fresh air if OAT is 85°F and RA is 71°F?
(85 x 20) x (71 x 80) = 73.8F
what is used whith the IAQ setting?
co2 detector
where should the answer from 16 be located?
in the space or building
when is the freeze protection enabled?
OAT below 45F
explain why freeze protection is required when useing an economizer?
if temp drops below 45F, risk of air blowing on water lines could cause freezing
what is the relationship between humidity and temperature?
as humidity goes up, temperature goes down
what is the porpose of the discharge sensor?
to maintain a 55F discharge or mixed air into the space
what are the terminals is the discharge thermostat hooked up to? (Honeywell logic module)
T & T1
how do youtest the mixed air/discharge sensor?
attach ohmmeter to 2 wires on sensor and check the chart
what is imporyant to check on the enthalpy sensor?
polarity So and S+
