Objectives Ventilation analysis with HOP Human exposure/IAQ Ventilation and energy

House of Pressure Demonstration Blower door pressurization Combustion safety Pressure diagnostics (series leakage)

Human Exposure Indoor air is largely about health effects What mass of environmental fluids (air, water) do we ingest over a course of a day?

What metrics for human exposure? Concentration Exposure Dose Absorbed dose

Does Concentration Matter? Concentration Varies in space and time Exposure Dimensions of concentration × time

Presented Dose How much gets into body Dimensions of mass (usually) Assumes linear dose-response relationship

Absorbed Dose Not all of a dose is absorbed

Summary Concentration is not enough Ventilation has significant impact on indoor air quality You have tools for models

Source: DOE

Ventilation Sherman, M., and Matson, N., LBNL-39036

What are the components of energy use associated with ventilation? Sensible heat Energy associated strictly with an air temperature change Latent heat Energy associated with a change in absolute humidity Can be dominant portion of cooling load Fan energy Negligible if heating and using electric resistance

Infiltration and Ventilation Infiltrating air caries sensible energy q = M × C × ΔT [BTU/hr, W] M mass flow rate = ρ × Q [lb/hr, kg/s] ρ air density (0.076 lb/ft 3, 1.2 kg/m STP) Q volumetric flow rate [CFM, m 3 /s] C specific heat of air 0.24 BTU/(lb °F), kJ/(kg STP For similar indoor and outdoor conditions ρ and C are often combined q = 1.08 BTU min/(ft 3 °F hr ) × Q × ΔT Q [CFM]

Latent Infiltration and Ventilation Can either track enthalpy and temperature and separate latent and sensible later q = M × ΔH[BTU/hr, W] Or, track humidity ratio q = M × h fg × ΔW h fg = ~1076 BTU/lb, 2500 kJ/kg M = ρ × Q [lb/hr, kg/s]

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) For comfort parameters use Chapter 8

Absolute Temperature (T) (K, R) Dry-bulb temperature (t) [°F, °C] Wet-bulb temperature (t*) Dew-point temperature (t d ) Temperature

Humidity Humidity ratio (W) [lb/lb, g/kg, grains] 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,  ) [%] Saturation

What is enthalpy? Enthalpy is total energy in the air Sensible plus latent You can choose to track enthalpy, but then you don’t get any sense of sensible/latent split

Examples What is enthalpy of air in the classroom right now? Condensation on windows when taking a shower How cold does it have to be outside for condensation to form on windows? –Assumption is that windows are the same temperature as outside air –80 °F, RH = 80%

What conditions should you use for calculations? Design Outdoor – ASHRAE 1% and 99% values Indoor – ASHRAE comfort zone Energy use (i.e. operating) Hourly data TMY data

ASHRAE Weather 2001 Fundamentals ch.27

Summary Calculate sensible and latent energy separately Can combine into enthalpy Ventilation energy consequences are linear with Mass flow rate of air Humidity ratio difference Temperature difference

Ventilation and Energy Efficiency Avoid losses from ventilation Air-to-air heat exchanger Eliminate needs for fans Passive ventilation Offset cooling/heating load Economizer Nighttime flush

Avoid losses from ventilation Need to supply some amount of air Air-to-Air heat exchanger Adds efficiency multiplier to sensible (and sometimes latent) heat losses/gains due to ventilation Mechanical Increase reliance on ventilation instead of infiltration “Build tight, ventilate right.”