Chapter 9 Flashcards
Heat and humidity measurement terms
1) Sensible Heat (change of temperature) - the heat tat changes the temp of a substance
2) Latent heat (change of state) - does not change the temp; it is the heat that is absorbed or released by a substance when that substance changes state
3) British thermal unti (BTU) - measures the quantity of heat; the amount of heat that flows from one substance to another in one hour; the amount of heat that must be added to 1 lb of water to raise the temp 1 degree
4) Dry Bulb (DB) temp- the temp as indicated by an ordinary thermometer
5) Wet bulb (WB) temp - temp indicated by a thermometer with its a bulb covered by a water-wetted wick
5) Relative humidity - a measure of the water vapor in the air
6) Dew Point - the temp at which a sample of air will have a RH of 100%
7) R Value - measures the resistance to heat flow and is the reciprocal of the U Value
8) U Value - the rate of heat flow through materials; the overall coefficient of transmission
What is Mean Radiant Temperature (MRT) and how does it relate to radiation?
An average of the temperatures of all the surfaces in a direct line of sight of the body. If the MRT is lower than the body temperature, the body radiates heat to the surfaces around it. If the MRT us higher that the temp of the skin and clothing, the surfaces surrounding the person radiate heat towards the person.
How does load impact HVAC design?
When a system is designed, the total heat load for each space is carefully calculated and designed accordingly.
HVAC design consideration
1) RH does not adversely affect comfort as long as it is between 30 and 60%.
2) Air temp and MRT should be programmed and designed together
3) Tempered air is often introduced into the space neat the outside walls and windows to minimize the cold wall effect
4) Air velocity is not important if it is less than 50 feet per minutes
5) Short cycles of temperature and humidity changes are sources of discomfort and should be avoided
Optimum indoor HVAC design conditions for temp and humidity
between 71 degrees at 50 percent RH in winter to 76 degrees at 50 percent RH in summer
Benefits of building zoning
You have better control over the temp controls of different areas
Types of internal heat loads
1) People
2) Lighting - most significant source
3) Equipment - appliances
4) System - ducts and piping
Types of external heat loads
1) Solar 2 - 10 hour lag;
2) Ventilation and infiltration - outside air
SBS an BRI (building related sickness) symptoms
1) SBS -general discomfort, adverse reactions, or sickenss
2) BRI - diagnosed illness (legionnaires)
