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12 Cards in this Set
- Front
- Back
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What is a buildings heating load? When does maximum heating load occur? |
It is a buildings maximum heat loss during the heating period. When the outside temp is lowest. |
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What's is the general design tem p for HVAC? What is HVAC basically a practical application of? |
Anywhere between 21.1 to 22.2
Psychrometrics |
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What is total resistance R? What are eqs for R? |
It is the total resistance to heat flow through the entire thickness of material.
R = 1 / C and k = R / L k is the conductivity, resistance per unit thickness of the material L is length or thickness. |
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What is eq for heat transfer through walls, Windows, doors, and ceilings? What is U and how is it found? |
Qdot = U*A*(Ti-To)
Overall heat transfer coefficient. U = 1/sum(R) = 1 / [1/hi + sum(L/k) + sum(1/C) + 1/ho]. |
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What is ventilation? What is sensible heat? What is latent heat? What are eqs for both? Which is usually more significant? |
Ventilation is providing air and humidification to an occupied space.
Sensible heat is pure thermal energy that increases airs dry-bulb temp
Latent heat is moisture that increases airs humidity ratio.
Qs = mdot*cp*(Tid-Tin)=Vdot*density*cp*(Tid-Tin). Where Tin is dry bulb temp of air entering room
Ql = mdotwater*hfg = mdotair*∆w*hfg= Vdot*density*∆w*hfg
Sensible loads usually more significant and ventilation can be determined solely on that. However latent becomes more considerable if large moisture sources are present |
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What is the sensible heat ratio? What is the latent factor? |
SHR = Qdotsensible / (Qdotsensible +Qdotlatent) LF = 1 / SHR |
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What is the bypass factor? What is the lever rule i can use to find it? how do i find it graphically? |
It is the ratio of the bypassed air to the total AMT of air.
BF = (Tmix - Tcond) / (Troom - Tcond) Plot the two points on the psychrometric graph. The indoor design conditions (dry bulb and wet bulb temps) and the sat temp (ususlly of air leaving a/c) or dew-point temp same thing. Then plot a line between the 2 pts. Then the BF will be the distance of the conditions of air entering the space to the Sat temp pt over the total length of the line plotted.
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How do you use sensible heating ratio on psychrometrics chart? |
Use them protractor at the top to find the slope and then plot the line. |
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What is saturation %? |
Another way to say relative humidity |
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When a problem mentions air passing through a reheater and being raised sensibly what does that mean? |
If temp is being raised sensibly it is a represented by a horizontal line on the psychrometrics chart |
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If I know the dry-bulb and wetbulb temps what can I find for air at those conditions on the psychrometric chart? |
v specific volume and w humidity ratio. |
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If I am given wet bulb and dry bulb conditions for air for in and them have the relative humidity % of exit air what do I on the psychrometric chart to find exit conditions? If it's adiabatic (no heat applied) |
Basically from the pt that corresponds to given db and wb temps from a line up and to the left following constant enthalpy until it intersects with relative humidity line. |
