Class Objectives Stress the importance of HVAC Identify and compare factors that affect thermal comfort in buildings Calculate quantities from a psychrometric chart

HVAC Affects: Energy use (outdoor air quality) Peak demand Indoor air quality Occupant comfort and productivity Building cost

Primary energy vs. End use energy 1kWh (3.6MJ) of source energy (fuel) ≠ 1kWh of electric energy End use energy amount of energy delivered to consumer electric, heating, cooling Primary energy amount of energy delivered to consumer energy sources used to produce this energy + Example: conversion and transmission losses in power plant and delivery systems

Energy efficiency vs. Thermal efficiency Heating the residential house Thermal efficiency 100% Electric heater Power plant 100% Primary energy (gas) ~ 33% Electric energy End use ~ 33% For heating Energy efficiency 33% Thermal efficiency 75% Furnace heater Transport End use ~73% For heating 100% Primary energy (gas) ~ 97% Gas energy Energy efficiency 73% Page 17 Tao and Janis

LEED – Leadership in Energy and Environmental Design Green building rating system High-performance and sustainable buildings Voluntary (at this moment) national standard Affect Location environment – sustainable site Use of energy Use of water resources Use of building materials IAQ Design process

Thermal Comfort Combination of Human body - Indoor environmental factors Personal factors Human body - in thermal equilibrium with the environment

Thermal comfort equation - P.O.Fanger Energy balance for human body Metabolic Heat - Work = Energy that body release

Thermal comfort Metabolism – health condition and activity Clothing level Air Temperature Mean Radiant Temperature Air Velocity Humidity P.O. Fanger PPD – Predicted Percentage of Dissatisfied Scale 5-100%

Thermal comfort Factors that we control in buildings Air Temperature Humidity Air velocity Surrounding Temperature

Overview Psychrometric quantities Heat loss and gain Cooling, heating, and ventilation loads Cooling and heating equipment Air equipment and controls

Willis Haviland Carrier - Carrier 1911 "Rational Psychrometric Formulae”

Psychrometric Chart Need two quantities for a state point Can get all other quantities from a state point Can do all calculations without a chart Often require iteration Many “digital” psychrometric charts available Can make your own Best source is ASHRAE Fundamentals (Chapter 6)

Temperature Absolute Temperature (T) (K, R) Dry-bulb temperature (t) [°F, °C] Wet-bulb temperature (t*) Dew-point temperature (td) Mean radiant temperature (tr) Operative temperature (to) Effective temperature (ET*)

Which temperature do you expect to be higher? Wet-bulb Dry-bulb

Wet-bulb temperature (t*) Temperature measured by a psychrometer Lower than dry-bulb temperature Evaporating moisture removes heat from thermometer bulb The higher the humidity Smaller difference between wet-bulb and dry-bulb temperature

Dew-Point Temperature, td Define temperature at which condensation happen td is defined as temperature of that air at saturation i.e. RH = 100% Surfaces below the dew point temperature will have condensation Measured with a chilled-mirror apparatus

If you have a sample of air at its dew-point temperature? The water will condense out. It will be pure water vapor. Putting the sample in a sealed container and heating it will cause condensation. Putting the sample in sealed container and cooling it will cause condensation.

Humidity Humidity ratio (W) [lb/lb, g/kg, grains] [grains/lb = 1/7000 lb/lb] Relative humidity (RH, ) [%] Saturation

Humidity Ratio, W Mass of water vapor/divided by mass of dry air Orthogonal to temperature Not a function of temperature Most convenient form for calculations involving airflow Very hard to measure directly

Relative Humidity, RH or  Ratio of partial pressure of water vapor to partial pressure of water vapor at same T and P at saturation Strong function of temperature For constant humidity ratio Higher temperature, lower relative humidity Saturation

Relative Humidity Driving force for moisture transport Human comfort Moisture absorption/desorption Can be measured with Resistive sensors Capacitive sensors Horse hair

Conclusions Define thermal comfort parameters Define all quantities on a psychrometric chart and use it to do calculations

Reading Assignment Chapter 1 and Chapter 2 (Section 2.1 & 2.2) Tao and Janis Next class – Thursday 5 minutes quiz at the beginning of the class