Upload
sooraj-vs
View
227
Download
0
Embed Size (px)
Citation preview
7/23/2019 4.Heat Load Calculations211207
1/41
Heat Load Calculations
7/23/2019 4.Heat Load Calculations211207
2/41
Building Survey
The orientation of the building is thefirst parameter that a hvac engineer
should know before designing the
system required. The south westcorner of the building will susceptible
to the most intense heat rays from the
sun if it is e!posed" compared to allother corners. So the heat transfer
through that part will be higher.
7/23/2019 4.Heat Load Calculations211207
3/41
#ield sketches complete
architectural drawings civilplans are the basic aspects of
the good survey. $very H%&C
engineer should be aware
about the importance of
building survey.
7/23/2019 4.Heat Load Calculations211207
4/41
'se of Space
&pplication of the conditioned
space is another parameter.
(ffice Hospitals restaurantsfactories machine shops etc.
&ccording to the application
the air conditioning system will
differ.
7/23/2019 4.Heat Load Calculations211207
5/41
)hysical *imensions of &ir
conditioning Space Length breadth height of the
space+ distance between floor
and ceiling+ distance betweenfloor and false ceiling is also
an important factor. The area of
the space to be air conditioned
is a very important data.
7/23/2019 4.Heat Load Calculations211207
6/41
Columns and Beams
Si,e depth location of
beams and columns
7/23/2019 4.Heat Load Calculations211207
7/41
Construction material
Type of material used forconstruction is another data
with which the heat transfercan be calculated. *ifferent
type of materials will have
different type of heattransmission coefficient.
7/23/2019 4.Heat Load Calculations211207
8/41
Heat transmission
coefficient is defined as therate of heat transferredthrough the building barrier.
-t is determined by ' /012/3 24 3 25 3 66667 where
2 is the resistance offeredby different type ofmaterials.
7/23/2019 4.Heat Load Calculations211207
9/41
Surrounding conditions
-t should be checkedwhether the e!terior of walls
windows and roofs areshaded by ad8acentbuildings or e!posed tosunlight whether thead8acent space is
conditioned or not.
7/23/2019 4.Heat Load Calculations211207
10/41
Location of *oors and
9indows
Type si,e and #requency of
use of the doors and
windows will affect theamount of heat transfer.
7/23/2019 4.Heat Load Calculations211207
11/41
Stairways Lift corridors
$scalators and open to non
air conditioned areas
-t is not easy to air
condition open spaces as
the level of infiltration will be
very high. This will result inwastage of air conditioning.
7/23/2019 4.Heat Load Calculations211207
12/41
(ccupancy
Total number of people in thespace to be air conditioned. $ach
and every human being will emit
a lot of heat energy due to themetabolic activity of human body.
*uration of the occupancy and
nature of activity should also be
known.
7/23/2019 4.Heat Load Calculations211207
13/41
Lighting
Type of lighting usedinside the space will be afactor as the lights usedwill emit lot of heatenergy. There are
different types of lightsaccording to which theheat emitted differs.
7/23/2019 4.Heat Load Calculations211207
14/41
The types of lightscommonly used areincandescent fluorescentrecessed and e!posed.
The amount of air flowshould be known or elsethe estimate should be
done on th basis ofwatts 0sq.ft.
7/23/2019 4.Heat Load Calculations211207
15/41
&ppliances
There will be differenttypes of appliances and
equipments used in the space
to be air conditioned Theequipment will deliver some
heat inside the space to beconditioned.
7/23/2019 4.Heat Load Calculations211207
16/41
Business machines
electronic equipment etc canbe present in the area to be
conditioned. The locationwattage rating and whether it is
hooded or not are the different
types of parameters to bechecked.
7/23/2019 4.Heat Load Calculations211207
17/41
%entilation required There are different standards set for
the different type of requirements. C#:0sq. ft
C#:0person
C#:0room
These parameters should also be
taken in to account. %entilationrequirement will in turn play aimportant role in maintaining good
indoor air quality.
7/23/2019 4.Heat Load Calculations211207
18/41
-ndoor unit and outdoor unit
location )arameters for indoor unit location
are There should be no obstruction to
air flow and distribution ofconditioned air. There should enough space for
servicing. )iping and wiring work can be easily
connected. There should be a solid wall or
ceiling to mount the unit.
7/23/2019 4.Heat Load Calculations211207
19/41
)arameters for outdoor unitlocation are
There should be good aircirculation
There should be no other ma8orheat interference.
The e!haust air should not besucked in once again for
recirculation. The unit should not be kept
very close to corrosive
materials or environment.
7/23/2019 4.Heat Load Calculations211207
20/41
$stimation of heat load
#or summer air conditioning the airconditioned space has to be maintained
at a lower temperature than the
surrounding temperature. The moisturelevel also should be maintained at a lowe
level compared to the atmospheric level.
So there has to be heat transfer betweenthe conditioned space and the
surroundings.
7/23/2019 4.Heat Load Calculations211207
21/41
&fter building survey a H%&C
engineer should know the amount
of heat transfer that should take
place between the space to be
conditioned and the surroundings.#or this heat load calculation and
estimation is required. Hence it is
required for the design andselection of air conditioning
equipment.
7/23/2019 4.Heat Load Calculations211207
22/41
;eneral )rocedure
To calculate a design
cooling or heating load
information about buildingdesign and weather data at
design conditions should beprepared.
7/23/2019 4.Heat Load Calculations211207
23/41
(utside design conditions
The first important step is to
fi! the peak outside
condition. ie+ the date andtime of year when the peak
conditions can prevail.
7/23/2019 4.Heat Load Calculations211207
24/41
-nside design conditions
-ndoor air temperature to be
maintained in each space
should be dictated by theapplication.
S l t i i i th h
7/23/2019 4.Heat Load Calculations211207
25/41
Solar transmission gain through
walls roofs glass and partitions
&s a result of absorption of directradiation of sun temperature of wall
roof glass and partitions rises
above the ambient temperature.This results in large temperature
difference with respect to the airconditioned space. The heat
transfer coefficient or '
7/23/2019 4.Heat Load Calculations211207
26/41
7/23/2019 4.Heat Load Calculations211207
27/41
7/23/2019 4.Heat Load Calculations211207
28/41
7/23/2019 4.Heat Load Calculations211207
29/41
Then compute the heat
transmission loss for each kind of
wall glass floor ceiling and roof in
each building by multiplying the
heat transfer coefficient in eachcase by area of the surface and
temperature difference between
indoor air and outdoor air orad8acent lower temperature spaces.
-nfiltration
7/23/2019 4.Heat Load Calculations211207
30/41
-nfiltrationCompute the heat loss associated with
infiltration through cracks and openingsof doors and windows. These valuesdepend on the kind of crack and temp.difference of indoor and outdoor air. Theair blowing in the opposite direction ofthe building which is higher in moisturecontent and temperature to infiltrate
through the cracks and openings. Thisresults in the sensible and latent heattransfer to the conditioned space and
locali,ed heat gains.
7/23/2019 4.Heat Load Calculations211207
31/41
% til ti
7/23/2019 4.Heat Load Calculations211207
32/41
%entilation
9hen positive ventilation
using outside air is providedto the conditioned space
energy required to conditionthis air to the temperaturerequired must be provided by
the unit. So associated loaddue to fresh air should also becalculated. This is consider as
a forced infiltration.
7/23/2019 4.Heat Load Calculations211207
33/41
7/23/2019 4.Heat Load Calculations211207
34/41
-nternal Heat ;ain
-nternal heat gain throughoccupancy lights and otherappliances should also be
calculated. Human body throughmetabolism generates heat withinitself and releases it by radiation
convection and evaporation fromthe surface. -lluminants will convertelectrical power to light and
sensible heat.
7/23/2019 4.Heat Load Calculations211207
35/41
9hy we require fresh airopening in the air
conditioning system=
- d &i > lit
7/23/2019 4.Heat Load Calculations211207
36/41
-ndoor &ir >uality
%entilation or outside fresh air in to
the air conditioned space is veryimportant. -t is to replace the o!ygenconsumed and to dilute the carbon
dio!ide and pollutants in the air.)ollutants are like bacteria fungusdust materials chemicals etc.Therefore it is important to removethe contaminants so that we canimprove the indoor air quality.
#resh air intake will never remove
7/23/2019 4.Heat Load Calculations211207
37/41
#resh air intake will never removethe contaminants but they willdilute them so that thecontaminants can be kept in thepermissible limits according to thestandard levels. (dour removal is
handled by introducing freshoutdoor air in to the air handlingunit. This air is mi!ed with the
return air to improve the air quality.This should be be done beforegetting the air treated at the
cooling coil.
7/23/2019 4.Heat Load Calculations211207
38/41
&pplication C#:1%ol.of#resh air7
(ffice Space 4?
2estaurants 4?
Bars 5?
Conference room 4?(perating rooms 5?
Supermarkets /@
&uditoriums /@
Laboratries 4?
Hotel rooms 5?
7/23/2019 4.Heat Load Calculations211207
39/41
The following steps can improve
indoor air quality
:aintain a slight positive pressure
inside the conditioned space so
that infiltration can be prevented. &ir filtration is very important so
that the particulates can be
prevented from passing on to theconditioned space.
7/23/2019 4.Heat Load Calculations211207
40/41
Cleaning of supply return and fresh airducts at the time of commissioning and a
regular intervals of operation. The condensate should be prevented
from getting stagnant in the drain pan.
The condensate will become a breedingpoint of bacteria and fungi.
&void fibre glass lined &H'As+ since it isinert by itself once it becomes wet thenit will become a collection area ofparticulate material and microbial growth.
7/23/2019 4.Heat Load Calculations211207
41/41
)2($CTS