Mid Term Review

Question 1

List 5 things you can do to a space?

Answer 1

Heat it
Cool it
Dehumidify
Humidify

Question 2

Two ways to get fresh air into a house?

Answer 2

Infilitration
Ventialtion

Question 3

Sizing a HRV into a house, whats the percentage ?

Answer 3

40%

Question 4

House us 2000sqft. 8ft ceiling, find cubic feet ? 40%
20F outside
70F inside

Answer 4

Remember (.4) and (60%) Find CFM -> remember (1.08) and use equation with TD

20008=16,000c.u.FT4
.4 from the 40% = 6400 cu.FT/HR. Divide it by 60
6400/60= 107cfm
Qs= 1.08CFMTD -> Qs= 1.08107 50, TD from 70-20=50
5,778Btus/HR

Question 5

3 Ton Evap
Too much cause coil to ice up (T/F)
Less would cause coil to ice up
(T/F)

Answer 5

Too much in coil is (False)
Less in coil is (True)

400

Question 6

Difference between comfort cooling coil compared to commercial comfort coil is ?

Answer 6

Radiator is tighter in comfort cooling

Commerical coul is wider

Question 7

Per ton how many CFM

Answer 7

400

Question 8

Whats summer temp comapred to winter temp ? Offsets what ?

Answer 8

Summer is 75/50
Winter is 70/35 and winter tempature offests with humidity.

Question 9

Where is the distributer?

Answer 9

Before the Evaporator.

Question 10

3 ways heat leaks into a building?

Answer 10

Infiltration
Conduction
Convection

Question 11

Which one will increase or decrease heat gain?

Answer 11

Hint (All the above)

Direction the house is facing
Insulation
Types of window/door

Answer 12

Dx direct expansion
Geothermal
Evaporation cooling

Question 13

Location of common parts refridgeration components?

Answer 13

Metering device- in where the evaporator coil is, inside unit
Accumalator- outdoor, suction line, before compressor

Question 14

Difference between sensible and latent heat?

Answer 14

Lowering wet bulbs or humidity is latent heat

Lowering measurable temp is sensible heat

Question 15

75 Air 50% humidity - measuring in the plenum, what will happen to thr relative humidity?

Answer 15

Relative humidity goes higher
It’ll be 38 in the Evap 55F out the evap temp, 6 degree difference.

Question 16

15

Question 17

Multiple thermostat, houses parts diff temp?

Answer 17

ZONE SYSTEMS

Question 18

Lower Amp Draw ?

Answer 18

Undercharge

Question 19

Walk in cooling with TXV, whats the charging method?

Answer 19

Subcool

If fixed bore = superheat

Question 20

Medium temp refrigerant low on charge?

Answer 20

Superheat will be much higher than normal.

Question 21

In a refrigerant system low superheat is?

Answer 21

Overcharge

Question 22

See higher then expected AMP draw?

Answer 22

Overcharge, dirty coil, airflow issues

Question 23

High side pressure, convert into tempature, liquid line temp subtract from that what’re you looking at?

Answer 23

Subcool

Question 24

3 careers that are involved in installing AC unit?

Answer 24

Mechanical
Electrical
Sheet metal

Question 25

How can I control head pressure?

Answer 25

Variable Frequency Drive(VFD) Modulating compressor Fan cycling switch All the above

Question 26

Residential comfort cooling vs. commerical cooling?

Answer 26

No, they’re different including usage & needs

Question 27

230v +/-10% what voltage can it run at?

Answer 27

253 -> 207 better to run 208/230. 253 down to 177 broader range. Rated voltage up 253 down 207.

Question 28

High head pressure on a cap system equals what?

Answer 28

Reduce System Capacity

Question 29

Difference between R22 and R410?

Answer 29

Lower condensing temp

Question 30

If the compressors running what other components runs?

Answer 30

Commerical systems: evaporator fan, condensor may or may not be on.

Question 31

What is more efficient Air cool or water cool?

Answer 31

Water cool *GIVEN WATER TEMP* Add 20% 55 (105F) 55+ 20 = 85 85+30=115 10-15 for R410A

Question 32

Central Air Split System 3 loads on a residential system for call of cooling is?

Answer 32

1) compressor 2) condensor fan 3) Evap Fan

Question 33

Where to mount disconnect?

Answer 33

Line of sight between 25 Ft of equipment. Fill in the blank

Question 34

40 cut-in - 25 lb differential = 15 lb cut-out

Answer 34

40-25 = 15lb cut-out

Question 35

Two common safety controls?

Answer 35

1) Low pressure control 2) high pressure control

Question 36

24v 75VA -> 75VA / 24V = 3.125A

Answer 36

24v 40VA= 1.66A

Question 37

Wiring up more than 1 transformer?

Answer 37

Wire in parallel only

Question 38

Indication of _____ charge? Ice in evaporator

Answer 38

Undercharge

Question 39

Typical approach temp for indoor coil?

Answer 39

35 approach temp. Return Air - boiling temp 75F - 55F = 20 degree TD

Question 40

Schematic true line circuits. 208v - step-down Control voltage.

Answer 40

Trace the line of voltages passing.