Load Calculations

BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS

BUILDING LOAD CALCULATIONS

AgendaAgenda

• Heat Load Calculation Basics• Definitions• Thumb Rules• Questions


As an Example we will talk about theHeat Transfer SAY TO A HOTEL ROOMAs an Example we will talk about theHeat Transfer SAY TO A HOTEL ROOM



Heat Transfer SAY TO A HOTEL ROOMHeat Transfer SAY TO A HOTEL ROOM


AREA OF THIS ROOM IS 14.4 SQ M

WHAT IS THE WATTS / SQ M

WHAT IS THE AIR QUANTITY IN

L/S PER SQ .M


Sensible HeatSensible Heat

Heat which causes a change in temperature of a substance




UNITS:

METRIC : JOULES ………………….. POWER IS ….. WATTS : Joules / Second

IMPERIAL : BTU ( IS HEAT REQUIRED TO RAISE 1 LB OF WATER THROUGH 1 DEGREE F)

POWER IS : BTU/ HR OR TONS

WE TAKE ABOUT MACHINE CAPACITY (POWER) IN ‘TONS’ OR KILOWATTS

1 TON = 12000 BTU/HR AND 1 BTU = 1055 JOULES

= 12000 X 1055 / 3600 = 3513 JOULES/SEC = 3513 WATT = 3.513 KW




UNITS:

IN AN AIR-CONDITIONING SYSTEM :

TOTAL SENSIBLE HEAT = 1.23 X LITRES/ SECOND OF AIR X ( DB ENT – DB LEAVING)

IN A HOTEL ROOM CIRCULATING 154 LITRES / SECOND OF AIR

TOTAL SENSIBLE HEAT = 1.23 X 154 X (24 - 14.2 ) = 1856 WATTS


SAMPLE - HEAT LOAD CALCULATIONS

IMPORTANT EQUATIONS

SENSIBLE HEAT : 1.08 X CFM X T(°F) 1.23 X l/S X T(°C)

LATENT HEAT : 0.68 X CFM X W (gr/LB) 3010 X M3/S X W(kg/kg)

```````````````````````````````````````````````````````````````````````````or 3.01 x l/s x DeltaW(kg/kg)

TOTAL HEAT : 4.45 X CFM X H (BTU/LB) 1.20 X M3/S X H(KJ/KG)


Latent HeatLatent Heat

Heat energy absorbed in the process of changing form of a substance without a change in temperature or pressure. Heat energy that cannot be measured with a thermometer.

32o


Latent or Sensible?Latent or Sensible?

• What changed from previous slide

• What type of heat was involved

32o


Latent or Sensible?Latent or Sensible?

• What changed from previous slide

• What type of heat was involved

32o

LATENT HEAT IN AIRCONDITIONING SYSTEM =

2.96 X LITRES/SECOND OF AIR X GMS/KG DIFFERENCE

FOR A HOTEL ROOM THAT CIRCULATES 154 L/S OF AIR WITH ENTERING GMS/KG MOISTURE OF 9.32 AND LEAVING THE COIL WITH 8.82, THE LATENT LOAD = 2.96 X 154 X (9.32-8.82)

= 231 WATTS


What all information should we gather before we start with the Heat Transfer

calculation of this HOTEL ROOM

What all information should we gather before we start with the Heat Transfer

calculation of this HOTEL ROOM



INITIAL DESIGN CONSIDERATION

• BUILDING CHARATERISTICS

•CONFIGURATION

•OUTDOOR DESIGN CONDITIONS

•INDOOR DESIGN CONDITIONS

•OPERATING SCHEDULES

•ADDITIONAL CONSIDERATIONS LIKE FAN ENERGY,DUCT LEAKAGE,TYPE OF RA SYSTEM

(c) 1997 ASHRAE Handbook, Fundamentals, Chapter 28


HEAT GAIN CALCULATION CONCEPTS •GAIN THROUGH BUILDING FENESTRATION ( GLAZING AND ITS COMPONENTS)…. EXTERNAL SHADING

•OTHER EXTERIOR SURFACES

•SOL AIR TEMPERATURE

•INTERNAL GAIN THROUGH PARTITIONS

•SOURCES IN CONDITIONED SPACE LIKE PEOPLE,LIGHTING,APPLIANCES OR OFFICE EQUIPMENT

•INFILTRATION AND VENTILATION HEAT GAIN

•LATENT HEAT GAIN FROM MOISTURE THROUGH PERMEABLE BUILDING

•MISC… FAN…. DUCT HEAT GAIN

HEAT STORAGE CAPACITY OF ROOM IS IMPORTANT IN CONVERTING HEAT GAIN TO COOLING LOAD



• Load Calculations:• Space Sensible Load Calculations

• ‘SOLAR LOAD’• ‘TRANSMISSION AND CONDUCTION LOAD’• LIGHTING• EQUIPMENT LOAD• PEOPLE LOAD

• Calculating airflow based on Space Sensible Load• ‘Internal Loads’• ‘Skin Loads’

• Fresh air Load and therefore Cooling Coil Load

We will talk about :


Typical Ambient conditions

35°C @ 80% RH45°C @ 30% RH35°C @ 20% RH20°C @ 90% RH

45°C @ 30% RH

35°C @ 80% RH

20°C @ 90% RH

35°C @ 20% RH

35°C @ 80% RH45°C @ 30% RH35°C @ 20% RH20°C @ 90% RH


Comfort conditions

45°C @ 30% RH

35°C @ 80% RH

20°C @ 90% RH

35°C @ 20% RH

Comfort condition,20 to 24°C,

40 to 70% RH


Control the Humidity

Source: ASHRAE HVAC Systems and Equipment Handbook


All sensible loads downstream of the supply air ductwork and before the return air grill are part of the space sensible load!

Space Sensible Load - Well Mixed System



LETS TALK ABOUT Sun Loads





SOLAR LOAD:

• DEPENDS ON DIRECTION AND WHERE YOU ARE LOCATED

•DEPENDS ON AREA OF GLASS

•SHADING CO-EFFICIENT

•SOLAR HEAT GAIN FACTOR OF THAT LOCATION AND TIME

•COOLING LOAD FACTOR




SOLAR LOAD:

• DEPENDS ON DIRECTION AND WHERE YOU ARE LOCATED

•DEPENDS ON AREA OF GLASS

•SHADING CO-EFFICIENT

•SOLAR HEAT GAIN FACTOR OF THAT LOCATION AND TIME

•COOLING LOAD FACTOR

FOR OUR EXAMPLE HOTEL ROOM :

GLASS AREA IS 4.8 SQ.M

SHADING CO.EFF IS 0.42

GLASS FACES WEST AND THE COMPUTER CALCULATES THE SOLAR HEAT GAIN FACTOR AS 694 WATTS / SQ. M

AND THE LOAD FACTOR OF 0.64

THEREFORE HEAT GAIN =

4.8 X 0.42 X 694 X 0.64 = 895 WATTS

THIS IS THE LARGEST LOAD


Sun Loads



Ø = e. S. (T1-T2)

T

T1

T2

e

Ø

Ø (W) heat flux (W/m.K) thermal conductivityT1 (K) higher temperatureT2 (K) lower temperaturee (m) distance in xS (m²) Surface of exchange

Ø = e. S. (T1-T2)

CONDUCTION


WE WILL TALK ABOUT

Conduction gain – WALL AND GLASS

Typical Values of Thermal Conductivity

Typical Values of Thermal Conductivity

0.01 0.1 1 10 100 1000

GasesGases

InsulationInsulation

AlloysAlloys

Pure MetalsPure Metals

CO2 H2

Oils Hg

Foams Fibers

Plastics Oxides

Ni Al

Zn Ag

LiquidsLiquids

Nonmetallic SolidsNonmetallic Solids

H2O

Ice

(W/m*K)BUILDING LOAD CALCULATIONS


T

T1

T2

e

Ø

SIMPLY :

AREA X U FACTOR X COOLING LOAD TEMP DIFF


HOTEL ROOM EXAMPLE :

WALL AREA( FIRST WALL = 10 SQ M

U VALUE = 0.57 WATT/ SQ.M / DEG C

CLTD = 18

SCF = 0.65

GAIN WATTS = 10 X 0.65 X 18.8 X 0.57 = 103 WATTS

WALL 2 SIMILARLY IS 140 WATTS ONLY

GLASS CONDUCTION IS 4.8 X 19 X 2.1 = 194 WATTS






We will talk about :


• Internal Space Sensible Loads are comprised of several items:

• Lighting• People• Small Power

• Computer• Printers and copiers• Task Lighting• Coffee pots, microwaves and

refrigerators

‘Internal’ Space Sensible Loads


Lighting load :

• RESIDENTIAL : 10 WATTS / SQ. M

•SHOPS AND SHOWROOMS : 20 WATTS / SQ.M


Lighting load :

• RESIDENTIAL : 10 WATTS / SQ. M

•SHOPS AND SHOWROOMS : 20 WATTS / SQ.M

FOR OUR HOTEL ROOM WE ASSUME THAT WE HAVE A LIGHT OF 205 WATTS


REFER TO ASHRAE OR CHVAC PROGRAM

HOTEL EXAMPLE

4 PERSONS AT 70 WATT / PERSON ……… TOTAL 280 WATTS SENSIBLE

4 PERSONS AT 55 WATT / PERSON LATENT……… TOTAL 220 WATTS LATENT




WE NOW ADD ALL THIS UP AND TRY TO FIND THE

‘TOTAL SENSIBLE HEAT’

WALL1 =103

WALL2=140

GLASS TRANS =194

GLASS SOLAR=895

LIGHTS=205

EQUIPMENT=27

PEOPLE SENS =280

WE TAKE A SAFETY OF 5% AND THE TOTAL SENSIBLE LOAD IS 1845 WATTS


Cooling and Dehumidifying Process Example

L/s = Space Sensible Load (watts)

1.232 x (T setpoint - T supply)

L/s = 1845

1.232 X ( 24-14.3 ) = 154 L/s


VERY

IMPORTANT

FOR

DX

SYSTEMS


VERY

IMPORTANT

FOR

DX

SYSTEMS

FOR VENTILATION RATES

REFER ASHRAE

RECCOMENDED:

•ONE FRESH AIR CHANGE/HR

•OR

•7.5 L/S PER PESON

FRESH AIR IN THE MIDDLE EAST IS VERY EXPENSIVE


VERY

IMPORTANT

FOR

DX

SYSTEMS

ASSUME ONLY 12 L/S FOR OUR HOTEL ROOM

BASED ON

NORMALLY I TO 2 PERSONS NORMALLY OCCUPY

CALCULATE SENSIBLE AND LATENT HEAT PORTIONS


VERY

IMPORTANT

FOR

DX

SYSTEMS

ASSUME ONLY 12 L/S FOR OUR HOTEL ROOM

BASED ON

NORMALLY I TO 2 PERSONS NORMALLY OCCUPY

CALCULATE SENSIBLE AND LATENT HEAT PORTIONS

PROGRAM GIVES US 372 WATTS LATENT AND 284 WATTS SENSIBLE




NOW CALCULATE THE TOTAL SENSIBLE AND TOTAL LATENT LOAD TO DETERMINE THE COIL COOLING CAPACITY

ANSWER:

2860 WATTS

AIR QUANTITY : 165 L/S




AREA OF THIS ROOM IS 14.4 SQ M

WHAT IS THE WATTS / SQ M

WHAT IS THE AIR QUANTITY IN

L/S PER SQ .M




BE CAREFUL OF NOISE AND TURBULANCE WHEN YOU CROSS 14 LITRES/ SEC PER SQUARE M

•NOISE IS HIGH

•PEOPLE CAN FEEL A ‘DRAFT’


SAMPLE - HEAT LOAD CALCULATIONS

IMPORTANT EQUATIONS

SENSIBLE HEAT : 1.08 X CFM X T(°F) 1.23 X l/S X T(°C)

LATENT HEAT : 0.68 X CFM X W (gr/LB) 3010 X M3/S X W(kg/kg)

TOTAL HEAT : 4.45 X CFM X H (BTU/LB) 1.20 X M3/S X H(KJ/KG)






We talked about :


CONCEPTS

•Sensible Heat Ratio, Re-heat considerations, Bypass Factors and Cooling Coil types

•Variable Air Volume

•Air-Flow rate as a ratio to Floor Space and its importance – Relationship to ‘Noise’ and ‘Turbulence’

•Energy Considerations and benefits of Modulating Airflow

•Importance of Leaving Air Temperature and Humidity Control

•Part Load Considerations

•Apparatus Dew-point

•INDOOR AIR QUALITY



Overhead Delivery


Assigning Loads to Occupied Space



• ENERGY STAR Label Requires IAQ Compliance

• ... Then a professional engineer needs to submit verification that the building meets 3 standards for the indoor environment: ASHRAE Standard 62-2001; ASHRAE Standard 55-1992 for thermal comfort; and IESNA Lighting Handbook for lighting quality. The ENERGY STAR Label for Buildings is offered to the top 25% of buildings. The Label recognizes one year of performance, and encourages facility managers to apply annually. The Label was just introduced in January, 1999.


• External Space Sensible Loads include:• Glass Transmission• Solar Radiation• Infiltration• Wall Transmission

‘External’ Space Sensible Loads


• Coil Loads include:• ‘Internal’ loads• ‘External’ loads• Roof load• Ductwork heat losses or gains• Fan motor heat gains• Ventilation loads• Any other loads put on the system

which do not occur in the occupied space

Coil Loads


• Every HVAC System must take into account Space Sensible Loads.

• The particular method of handling loads changes, but the load remains the same.

Space Sensible Loads


CIRCULATIONZONE

Light GainTo Room

Ceiling GainTo Room

Occupants GainSensible & Latent

MiscellaneousEquipment Gain

PERIMETERZONE

INTERIORZONE

Light Gain to Return Air

Roof Solar & Transmission Gain to Return Plenum

Ceiling GainTo Room from

Lower Floor

Space Loads - Well Mixed System


Load Item Well-Mixed Loadto Space

CEV Load toSpace

Lights 12.9 watts/m2 9.0 watts/ m2 (70%) 2.6 watts/ m2 (20%)People 8.6 watts/ m2 8.6 watts/ m2 (100%) 8.6 watts/ m2 (100%)

Small Pwr. 32.3 watts/ m2 32.3 watts/ m2 (100%) 32.3 watts/ m2 (100%)

Raised Floor N/A <6.5 watts/ m2>

Total ‘Internal’ Load 49.9 watts/ m2 37 watts/ m2

Glass Solar253 watts/lm

253 watts/ lm (100%) 151.8 watts/ lm (60%)

Glass Transmission49 watts/ lm

49 watts/ lm (100%) 29.4 watts/ lm (60%)

Wall Transmission17.4 watts/ lm

17.4 watts/ lm (100%) 17.4 watts/ lm (100%)

Infiltration12.1 watts/ lm

12.1 watts/ lm (100%) 7.3 watts/ lm (60%)

Total ‘External’ Load 331.5 watts/ lm 205.9 watts/ lm

Typical Assignment of Loads to Space


Psychrometric Analysis



Typical Values of Thermal Conductivity for Metals

Used in Heat Exchangers

Typical Values of Thermal Conductivity for Metals

Used in Heat Exchangers

Aluminum alloy 120 160 180 -

Steel, carbon - 43 42 36

Stainless steel 16 17 19 19

Copper 407 380 374 350

Brass 88 100 120 140

Nickel/chrome 12 13 16 18

-80°C -20°C 40°C 200°CW/(m.K)


Summary – Building Load CalculationSummary – Building Load Calculation

Factors that affect the Building Load

Overall Heat Transfer Co-efficient

External Loads

Internal Loads

Ventilation requirement and Indoor Air Quality

Air Quantity and Cooling Capacity

Load on the cooling coil


Overhead Delivery

Questions ?????


UPG TAINING FEB’2006

!

Load Calculations

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