Example of thermal radiation spectra for black and gray surfaces at room temperature

max = 5216 microns T(o R)

The CMB has a thermal black body spectrum at a temperature of 2.72548±0.00057 K.[4]

4. The Temperature of the Cosmic Microwave Background, Fixsen, D. J. ,The Astrophysical Journal, Volume 707, Issue 2, pp. 916-920 (2009)

(2.72 oK = 4.90 o R)

max = 5216 microns - oR

4.90 oR

max =1064.49 microns

04/19/23 2

micron10 microns10,000 microns1,000,000 microns 0.01 micron 0.0001 micron 0.000001 micron

CMB*

The invention of the laser, which stands for light amplification by stimulated emission of radiation, can be dated to 1958 with the publication of the scientific paper, Infrared and Optical Masers, by Arthur L. Schawlow, then a Bell Labs researcher, and Charles H. Townes, a consultant to Bell Labs. 

* Penzias story by Arthur Schawlow

Near-infrared NIR, IR-A DIN 0.75–1.4 µm 0.9–1.7 eVDefined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles.

Short-wavelength infrared SWIR, IR-B DIN 1.4-3 µm 0.4–0.9 eV Water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the

dominant spectral region for long-distance telecommunications.

Mid-wavelength infrared

MWIR, IR-C DIN; MidIR.[7] Also called intermediate infrared (IIR)

3–8 µm 150–400 meV

In guided missile technology the 3–5 µm portion of this band is the atmospheric window in which the homing heads of passive IR 'heat seeking' missiles are designed to work, homing on to the Infrared signature of the target aircraft, typically the jet engine exhaust plume. This region is known as thermal infrared, but it detects only temperatures somewhat above body temperature.

Long-wavelength infrared LWIR, IR-C DIN 8–15 µm 80–150 meV

The "thermal imaging" region, in which sensors can obtain a completely passive image of objects only slightly higher in temperature than room temperature, (for example, the human body), based on thermal emissions only and requiring no illumination such as the sun, moon, or infrared illuminator. Forward-looking infrared (FLIR) systems use this area of the spectrum. This region is also called the "thermal infrared."

Far infrared FIR 15–1,000 µm 1.2–80 meV (see also far-infrared laser and far infrared).

Microwave 1 mm – 1 meter 300 GHz – 300 MHz 1.24 meV – 1.24 µeV

Extraterrestrial daily horizontal irradiation as function of day of year, for north latitudes

It is measured by satellite to be roughly 1366 watts per square meter,[2] though it fluctuates by about 6.9% during a year - from 1412 W/m2 in early January to 1321 W/m2 in early July, due to the earth's varying distance from the sun.

Watts/m2 reach earth is considerably less and nearer to 1000 watts/m2

*m = number of air masses light must traverse

Clear day irradiance as function of zenith angle, under midlatitude conditions for visibilities of 5 km and 23 km at January 21 and July 21 for northern hemisphere

Normal I dir

Diffuse I diff

ASHRAE Clear Sky Model

ID =G ND = A * C N where G ND = normal direct radiation

exp (B/ sin B ) A = apparent solar irradiation at zero air mass B = atmospheric solar extinction coefficient Beta = solar altitude C N = clearness number

ID= G D = G ND coswhere theta is angle between sun’s rays and the normal to the surface

CLEAR SKY RADIATION ( H.C. Hottel)

I dir = Io[a o = a1* exp( -k/cos s)], Io = extraterrestial irradiance

I diff = (0.271*Io – 0.239 I dir)* ( cos )s

Liu and Jordan Diffuse Radiation on a Horizontal Surface

G t = G ND + G d + G R = ID + Id + IR

Correlation between diffuse irradiance and global irradiance (hourly averages, on horizontal) and hourly clearness index

k T = Iglo

IoCos(zenith

Hourly Clearness Index :

I diff = 0.09511-0.0164kT+4.388kT2 –16.638kT

3+12.336kT4

I glo

0.22<KT <0.80

I diff = 1.00 – 0.09kT , 0<k T<0.22 I glo

I diff = 0.165 , 0.80 <k T

I glo

KT = Daily Equivalent of k T

Monthly average daily total irradiation on vertical surfaces in January, April and July, as function of monthly average clearness

index and latitude

04/19/23 10

What if I lived in a tin shack in “the mission?”

Absorbed solar

radiation

Importance of thermal diffusivity of curtain wall.

ExternalOr

Internal Surface ??

N

U curtain wall = 0.180 BTU/hr-ft 2 F

U window installation = 0.60 BTU/hr-ft 2 F

U roof layer = 0.110 BTU/hr-ft 2 -F

N = 16 floors above 1st floor

13’

70 ‘

50 ‘U door = 0.200 BTU/hr-ft 2 F

6’

8’

25’

4’

04/19/23 12

Radiant Heat and Convective TransferA Simplification of the Complex, External Surface Boundary Condition

Radiant Energy must first be absorbed by surfaces that enclose the space and the objects in the space. When these objects and surfaces become warmer than the surrounding air, some of their heat transfers to the air by convective heat transfer.

Tsi (t)

T air (t)

What is relationship between Io(t) and cooling load (t), T air(t)?

Sol-Air Temperature Concept for Opaque Surfaces

q/A = hconductance* (T sol air surface – T es)

= hconductance * (T oa – T es ) + I sin() – *cos()*(IR)long

T sol air surface = Toa + I/hcond ) – (/hcond)*cos()*(IR)long …..Sol-Air Temp. to simplify wall heat transfer B.C.

T sol air temperature = Toa + I sin() - cosIR; Normally, IR)lw = 21 BTU/hr-ft2

ho ho

If /ho = 0.15 ( light colored surfaces) , then T = 3 – 4 o F

i.e., /ho = 0.30 for dark colored surfaces)Resulting in the temperature effects for various and ho T = 7 o F for = 0.9 and ho = 3 BTU/hr ft2F ,

Itotal(t) = Idir(t)+Idiff(t)+Iref(t)

BTU/hr-ft2

t(hr)SHGF

(glazing) Io (wall) Toa(oC)*10 Toa(oC) Toa(oF) T sol air (oF)0 0 0.0 1 0 0.0 156 15.6 60.08 60.12 0 0.0 150 15 59 59.03 0 0.0 172 17.2 62.96 63.04 0 0.0 172 17.2 62.96 63.05 2 2.3 161 16.1 60.98 61.76 137 157.5 172 17.2 62.96 110.27 204 234.5 194 19.4 66.92 137.38 216 248.3 217 21.7 71.06 145.59 193 221.8 233 23.3 73.94 140.5

10 146 167.8 244 24.4 75.92 126.311 81 93.1 256 25.6 78.08 106.012 41 47.1 261 26.1 78.98 93.113 37 42.5 267 26.7 80.06 92.814 35 40.2 267 26.7 80.06 92.115 31 35.6 261 26.1 78.98 89.716 26 29.9 256 25.6 78.08 87.017 20 23.0 244 24.4 75.92 82.818 11 12.6 244 24.4 75.92 79.719 0 0.0 239 23.9 75.02 75.020 0 0.0 233 23.3 73.94 73.921 0 0.0 217 21.7 71.06 71.122 0 0.0 211 21.1 69.98 70.023 0 0.0 194 19.4 66.92 66.924 0 0.0 187 18.7 65.66 65.7

40 o N Latitude ; July 21; T o = (T o, max + T o, min)/2 = 85.0 o F T o, max = 95 o F, h o = 3. 0 BTU/hr-ft 2 – F, h inside = 1.46 BTU/h- ft 2 –F

T inside = 78 o F

Sol-air temperatures for horizontal and vertical surfaces as function of time of day for summer design conditions, 21 July at 40° latitude

04/19/23 15

Solar Related Loads : Orientation Specific ; Loads Realized Out of Phase

04/19/23 16

IR)lw

ho

T Sol Air

Isol

IR)lw

Isol

hi

IR)lw

Isol

hrad

04/19/23 17

Mechanism of Radiation Heat Transfer via Fenestration

U glaz = 1/hi + 1/(X glass/k glass) + 1/ho

hiho qiqo T glass

= components ofSolar Heat Gain Factor

T glazing

04/19/23 18

Radiant Heat Gain Associated with Phase Lags

Radiant Energy must first be absorbed by surfaces that enclose the space and the objects in the space. When these objects and surfaces become warmer than the surrounding air, some of their heat transfers to the air by convective heat transfer.

Io (t)

+ + = 1

Tsi

Ti

What is equation of thermal conduction and heat storage for block?What is relationship between T

block (t)and Ti (t)?

What is relationship between Io(t) and cooling load (t)?

I

Shading Coefficient, SHGF, SHGC and Radiative Heat Load

q/A = Uglaz(T oa design – T ia design) + I + hi T glaz inside env

I = hi T inside env+ ho T outside env

Combining equations (1) and (3) , with assumption T inside env ~ T outside env = Tenv

……….(3)….Energy balance of glass pane at steady state

q/A = Uglaz (T oa design – T ia design) + I + I hi /(hi + ho) = q/A) cond + q/A) solar

q/A) solar = I + (I * hi )/(hi + ho) = I*[ + hi /(hi + ho )]

F = + hi /(hi + ho ) single pane, double strength, 3mm thickness = 0.87………………ASHRAE reference glazing (measured)

Fdp = o /ho*dp + idp)*(1/ho + 1/hs) ……..double pane where 1/dp = (1/ho + 1/hs + 1/hi)

F DSA = 0.87 (measured) SHGF = F DSA * I incident = solar heat gain factor

Shading Coefficient = SC = F glazing in use / FDSA = F glazing in use / 0.87 = 1.15*F glazing in use

(q/A) radiative solar heat gain = SC*SHGF = SC* F DSA * I incident = SHGC * I incident

SHGC

…..(1)… Single pane glass

q/A) fenestration = q/A) conduction gain + q/A) solar gain

Center of Glass and Edge-of-Glass U values for a Variety of Space Materials“Ideal” = space material with same U value as the glazing

Shading Coefficient AnalysisTransmissivity, reflectivity, absorptivity as a function of angle of incidence

A = DSA (double strength sheet glass) = 0.055 , = 0.86 , = 0.085B = 6 mm clear glassC =6mm gray, bronze or green tinted heat absorbing glass

The Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from sunlight. The SHGC is the fraction of the heat from the sun that enters through a window. SHGC is expressed as a number between 0 and 1. The lower a window's SHGC, the less solar heat it transmits.

Shading Coefficient: A measure of the ability of a window or skylight to transmit solar heat, relative to that ability for 3 mm (1/8-inch) clear, double-strength, single glass. Shading coefficient is being phased out in favor of the solar heat gain coefficient (SHGC), and is approximately equal to the Shading Coefficient multiplied by 1.15.

The shading coefficient is expressed as a number without units between 0 and 1. The lower a window's solar heat gain coefficient or shading coefficient, the less solar heat it transmits, and the greater is its shading ability.

The fraction of external solar radiation that is admitted through a window or skylight, both directly transmitted, and absorbed and subsequently released inward. The solar heat gain coefficient (SHGC) has replaced the shading coefficient as the standard indicator of a window's shading ability. It is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits, and the greater its shading ability. SHGC can be expressed in terms of the glass alone or can refer to the entire window assembly.

Center-of-Glass U values for double and triple-pane glasses at ASHRAE winter design conditions

1/U glass = 1/ hi + 1/ h s + 1/ ho where h s = h rad + h con(d, v)

x < 0.3 in

What is practicallimiting x relative toEffectiveness?

Low-emittance (low-E) coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow. The principal mechanism of heat transfer in multilayer glazing is thermal radiation from a warm pane of glass to a cooler pane. Coating a glass surface with a low-emittance material and facing that coating into the gap between the glass layers blocks a significant amount of this radiant heat transfer, thus lowering the total heat flow through the window. Low-E coatings are transparent to visible light. Different types of low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain.

http://www.efficientwindows.org/lowe.cfm

High-solar-gain low-E glass is often made with pyrolytic low-E coatings, although sputtered high-solar-gain low-E is also available.

Spectrally selective glazing. Glazing that is transparent to some wavelengths of the solar spectrum and reflective to others. Typical spectrally selective coatings are transparent to visible light and reflect short-wave and long-wave infrared as well as UV radiation. Spectrally selectivity can be achieved with low-E coatings and/or high-performance tints.

Window Technologies: Low-E Coatings

q/A = Uglaz(TOA design – TIA design)

q/A) fenestration = q/A) conduction gain + q/A) solar gain

q/A = Uglaz(TOAdesign – TIA design) + I + hi T env …..(1)… Single pane glass

q/A) fenestration = q/A) conduction gain + q/A) solar gain

q/A = Uglaz(TOAdesign – TIA design) + I + hi T env…..(1)… Single pane glass

q/A) solar = I + (I * hi )/(hi + ho) = I*[ + hi /(hi + ho )]

Assumptions in Cooling Load Determinations

a. Weather conditions from a long term database (energy codes often specify what data can be used to minimize degree of oversizinga. Solar loads selected are those that occur on a clear day in the month selected for the calculationsa. Full occupancy assumedb. All equipment operating at reasonably representative capacityc. Lights operating as expected for a typical design occupancyd. Latent as well as sensible loads are considered.e. Heat flow is analyzed assuming dynamic conditions = heat storage in building envelope and interior materials considered

Buildings are classified as envelope-load-dominated and interior load dominated.

Internal Heat Gain Expressions

U = 0.042 BTU/hr-ft2-F = 0.9, I incident = 120 BTU/hr-ft2

Compare solarFractions of heat gainthrough wall vs. glazing

Heat Gain Building Element

Conduction Solar Component EnhancementSolar

Transmission Internal Sources

Curtain Wall UCW*(Toa - T ia) UCW *I*(/ho) - 0 NA Roof URoof*(Toa - T ia) Uroof*[I*(/ho) – cosIR/ho)] NA

Fenestration Uglaz*(Toa - T ia) hi*T sol = I + I hi /(hi + ho) SC* SHGF Occupants (sens) NA NA NA N occ * Table ValueOccupants (lat) NA NA NA N occ * Table Value

Equipment NA NA NA See ASHRAE TablesLighting NA NA NA 3.41WFulFsa

Infiltration NA NA NA 1.08*CFMinf *TVentilation NA NA NA 1.08*CFMven*T

4840*CFMven*WMotors NA NA NA 2545(P/EM)FumFLM

Miscellaneous

Conceptual Diagram of Meeting Heating or Cooling Load of a Space

Working Fluid Out

Working Fluid In

Thi

Tlo

Space ofEnvironmentalControlTset, %RH set

W H20

d(q)/dt = 500*GPM*(Thi – Tlo), BTU/hrVentilation

Exfiltration

Infiltration

Wind

Infiltration

Space ofEnvironmentalControlTset, %RH set

W H20

T outside

WH20