Lecture Objectives: Review, Discuss HW1a, and correct some typos Define Typical Meteorological Year (TMY) Boundary Conditions at Internal Surfaces

Solar components Global horizontal radiation I GHR Direct normal radiation I DNR Direct component of solar radiation on considered surface: Diffuse components of solar radiation on considered surface: Total diffuse solar radiation on considered surface: Diffuse solar radiation on horizontal surface:

Ground and sky temperatures (correction are marked by red text) Sky temperature Swinbank (1963, Cole 1976) model -Cloudiness CC [0-1] 0 – for clear sky, 1 for totally cloud sky -Air temperature T air [K]  clouds = (1 − 0. 84CC)( e[8.45(1 − 273/ T air )] ) CC T sky 4 = · 10 −6 (1 − CC) T air 6 + T air 4 CC·  clouds Emissivity of clouds: For modeled T sky the  sky =1 (Modeled T sky is for black body)

Wind Direction Wind direction is defined in TMY database: “Value: 0 – 360 o Wind direction in degrees at the hou indicated. ( N = 0 or 360, E = 90, S = 180,W = 270 ). For calm winds, wind direction equals zero.” U windward leeward Wind direction: ~225 o N

Weather data Design condition vs. Operation condition Design whether parameters: Winter -Temperature Summer -Temperature and RH - Solar radiation – clear sky no pollution

Weather data for ES analyses Representative (typical) data Characteristic for the location and longer period of time TMY, TMY2, TMY3 database –Typical Meteorological Year 2 (TMY2) –data files are created from the National Solar Radiation Data Base (NSRDB) –a solar radiation and meteorological database ( for TMY2 and for TMY3)

Typical Meteorological Year Large number of locations Very compact data base You need to use data reader (write your one ore use already developed) Find more about TMY3 at:

Typical Meteorological Year Structure (many weather parameters) Real data (no averaging) ………………… JanuaryFebruary August December

Boundary Conditions at Internal Surfaces

Internal Boundaries Window Transmitted Solar radiation Internal sources

Surface to surface radiation ψ i,j - Radiative heat exchange factor Exact equations for closed envelope Closed system of equations Ti Tj F i,j - View factors

Internal Heat sources Occupants, Lighting, Equipment Typically - Defined by heat flux –Convective Directly affect the air temperature –Radiative Radiative heat flux “distributed” to surrounding surfaces according to the surface area and emissivity

Internal Heat sources Lighting systems –Source of convective and radiative heat flux –Different complexity for modeling

Surface Balance Conduction All radiation components Convection Convection + Conduction + Radiation = 0 For each surface – external or internal :

Air balance - Convection on internal surfaces + Ventilation + Infiltration h1 Q1 h2 Q2 Affect the air temperature - h, and Q as many as surfaces - m air c p.air  T air = Q convective + Q ventilation mimi Ts1 Tair Uniform temperature Assumption Q convective = ΣA i h i (T Si -T air ) Q ventilation = Σm i c p,i (T supply -T air ) Tsupply

Distribution of transmitted solar radiation DIRECT solar radiation

Distribution of transmitted solar radiation diffuse solar radiation

Transmission for single and double glazed window,,,

Heat transfer for double glazed window

Emissivity of window surfaces What is low-e window? - What is the difference between low-e and highly reflective window? Low-e - reduce the U-factor

Air balance – steady state Convection on internal surfaces + Infiltration = Load h1 Q1 h2 Q2 - h, and Q surfaces as many as surfaces - infiltration – mass transfer (m i – infiltration) Q air = Q convective + Q infiltration mimi Ts1 Tair Uniform temperature Assumption Q convective = ΣA i h i (T Si -T air ) Q infiltration = Σm i c p (T outdoor_air -T air ) Q HVAC = Q air = m·c p (T supply_air -T air ) T outdoor air HVAC In order to keep constant air temperate HVAC system need to remove cooling load

Air balance steady state vs. unsteady state Q1 Q2 Q HVAC = Q convection + Q infiltration mimi Tair HVAC For steady state we have to bring or remove energy to keep the temperature constant If Q HVAC = 0 temperature is changing – unsteady state m air c p  air  = Q convection + Q infiltration

Homework assignment 1b West 10 m 2.5 m South conduction T air_in I DIR I dif Glass T inter_surf T west_i T west_o T south_i T south_oi T air_out Styrofoam I DIR I dif Surface radiation Surface radiation Top view