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BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
AgendaAgenda
• Heat Load Calculation Basics• Definitions• Thumb Rules• Questions
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
Heat Transfer SAY TO A HOTEL ROOMHeat Transfer SAY TO A HOTEL ROOM
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Sensible HeatSensible Heat
Heat which causes a change in temperature of a substance
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Sensible HeatSensible Heat
Heat which causes a change in temperature of a substance
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
BUILDING LOAD CALCULATIONS
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)
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Latent or Sensible?Latent or Sensible?
• What changed from previous slide
• What type of heat was involved
32o
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
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
(c) 1997 ASHRAE Handbook, Fundamentals, Chapter 28
BUILDING LOAD CALCULATIONS
• 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 :
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Control the Humidity
Source: ASHRAE HVAC Systems and Equipment Handbook
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
LETS TALK ABOUT Sun Loads
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
LETS TALK ABOUT Sun Loads
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
LETS TALK ABOUT Sun Loads
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
Sun Loads
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
T
T1
T2
e
Ø
SIMPLY :
AREA X U FACTOR X COOLING LOAD TEMP DIFF
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
• 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 :
BUILDING LOAD CALCULATIONS
• 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
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
Lighting load :
• RESIDENTIAL : 10 WATTS / SQ. M
•SHOPS AND SHOWROOMS : 20 WATTS / SQ.M
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Heat Transfer SAY TO A HOTEL ROOMHeat Transfer SAY TO A HOTEL ROOM
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
VERY
IMPORTANT
FOR
DX
SYSTEMS
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Heat Transfer SAY TO A HOTEL ROOMHeat Transfer SAY TO A HOTEL ROOM
BUILDING LOAD CALCULATIONS
NOW CALCULATE THE TOTAL SENSIBLE AND TOTAL LATENT LOAD TO DETERMINE THE COIL COOLING CAPACITY
ANSWER:
2860 WATTS
AIR QUANTITY : 165 L/S
BUILDING LOAD CALCULATIONS
Heat Transfer SAY TO A HOTEL ROOMHeat Transfer SAY TO A HOTEL ROOM
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Heat Transfer SAY TO A HOTEL ROOMHeat Transfer SAY TO A HOTEL ROOM
BUILDING LOAD CALCULATIONS
BE CAREFUL OF NOISE AND TURBULANCE WHEN YOU CROSS 14 LITRES/ SEC PER SQUARE M
•NOISE IS HIGH
•PEOPLE CAN FEEL A ‘DRAFT’
BUILDING LOAD CALCULATIONS
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)
BUILDING LOAD CALCULATIONS
• 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 talked about :
BUILDING LOAD CALCULATIONS
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
(c) 1997 ASHRAE Handbook, Fundamentals, Chapter 28
BUILDING LOAD CALCULATIONS
Overhead Delivery
BUILDING LOAD CALCULATIONSBUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
Assigning Loads to Occupied Space
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
• 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.
BUILDING LOAD CALCULATIONS
• External Space Sensible Loads include:• Glass Transmission• Solar Radiation• Infiltration• Wall Transmission
‘External’ Space Sensible Loads
BUILDING LOAD CALCULATIONS
• 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
BUILDING LOAD CALCULATIONS
• 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
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Psychrometric Analysis
BUILDING LOAD CALCULATIONS
BUILDING LOAD CALCULATIONS
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)
BUILDING LOAD CALCULATIONS
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
BUILDING LOAD CALCULATIONS
Overhead Delivery
Questions ?????
BUILDING LOAD CALCULATIONS
UPG TAINING FEB’2006
!
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