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24 Cards in this Set
- Front
- Back
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How do you plot a system balancing chart? |
(1) find your system capacity and evaporator temperature difference. 12,000 BTU/hr 10F difference (2) plot a point at 34F and 0 capacity and another point at the ideal balance point. (12,000 btu/hr and 24F SST) Connect the line (3) plot all the evap and compressor lines. (4) choose the system that has the same or lower SST. choose the system with the same or higher capacity |
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What is the condenser correction factor? |
Condenser capacity = evap tonnage x CCF
10 tons x 1.35 = 13.5 tons |
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Measurements needed for CCF? |
Back (Definition) |
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If you are given 3 condensers IN THE SAME BOX and each unit is rated for 18,000 BTU/hr at 10F TD what will be your second point is at (0 capacity and 40 set point) |
40F - 10F = 30F SST 3x 18,000 = 54,000 BTU/hr (X,Y) = (30F, 54,000 BTU/hr)
This only works if they have the same TD. If they dont then (because evaps are linear) you need to adjust all the capacities to be at the same TD. |
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What is your evap capacity at 7.5 TD If the evap is 3000BTU/hr at 10 F TD. |
(3000Btu/hr x 7.5 F)/ 10 TD = 2250 BTU/hr |
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Shift in box temperature? |
(1) draw your evap line as you would (x(box temp), y(0 capacity)) and (x(box temp -TD), y(rated capacity at TD))
(2) Move the box temp and 0 capacity (40F,0BTU/hr) to your new box temp. (3)move the theoretical TD and theoretical capacity (usually 10F TD at the rated capacity for the evap) (4) draw the new Evap line (5) find the new balance point (6) find the new actual capacity and actual temperature TD. |
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If you have a temperature penalty how does that effect the evap line on the graph, capacity and TD? |
(1) draw your first evap point: (box temp, 0 BTU/hr)= (x(1),y(1)) (2) draw your second evap point: theoretical TD then at rated capacity. This will give you your second point. (X(2),y(2)) (3) now draw your evap line and condenser line, find the actual capacity and actual SST. (4) now subtract your temperature penalty (ex:5F) and the evap line will move left. Your capacity will decrease and your TD actual will increase. (x(1),y(1)) -> (x(1)- 5F, y(1)) (X(2),y(2)) -> (X(2)-5F, y(2)) Your capacity before you added the temperature penalty was higher and your SST was higher. |
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What is my run time?
Theoretical Capacity is 19000 BTU/hr Actual capacity is 20,000 BTU/hr System uses electric defrost (18hrs max) |
(19,000 x 18 hr)/ 20,000 = total run time (What you need btu/hr x max run time)/ (what you have btu/hr) 17.1 hrs a day |
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Too short of a run time issues? |
Less oil return. |
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What is considered a bad evaporator TD? |
Below 8TD or above 15TD |
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Expected run time hours |
16 hours for natural defrost 18 hours for electric defrost 18 hours for time initiated 20 hours for hot gas defrost |
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Recommended td for walk in? |
Recommended TD 8-10 (walk in)
Reach in 15-20 (reach in) |
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TD below 8F is susceptible to? |
Bacterial growth |
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Walk in TD above 10F is susceptible to? |
Evaporator freezing up faster |
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Compressor capacity is rated in what? |
BTU/hr |
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When it comes to the capacity of the evap
It is known to be? |
The capacity is linear
The larger the TD the more it can absorb. |
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Compressor capacity are not linear the higher the suction pressure? |
More gas is processed through the compressor the HIGHER the capacity
The more refrigerant the denser it is the higher the pressure
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A shift in box temperature simply means we are using the same components just changing the…. |
Box design temperature |
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When considering temperature penalty on a balancing graph, we subtract the value of the…. |
Temperature penalty off the original balance point expected SST |
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A system capacity is usually expressed in? |
Tons of refrigeration |
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Why does a dirty coil freeze up? |
Dirty evap means lower SST Dirtier it gets the lower the SST. |
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An oversized evaporator will allow more flow than the compressor can handle? |
SST will increase and the TD will decrease |
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An undersized evaporator will cause a restriction in flow in regard to how much the compressor is allowed to process? |
This means the suction pressure will drop, increasing the TD |
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Why is getting a 2.5 ton coil acceptable in a location with no humidity? (Fixed orific system this works better) |
If the temperature difference is smaller then you wont remove as much humidity as quickly. |
