Download HEAT LOAD

User’s Guide
HEAT LOAD
CALCULATION PROGRAM FOR
HEAT LOSS AND COOLING LOAD
Summer
28°C
E.C. Boelman
D. van Geest
L. Diephuis
R. Philippa
TU Delft – Faculty of Architecture
Building services chair
2002-2006
Winter
-7°C
CONTENTS
1.
INTRODUCTION......................................................................................................................................... 1
2.
START UP OF THE PROGRAM ............................................................................................................... 1
3.
THE PROGRAM .......................................................................................................................................... 1
•
•
•
•
4.
Structure.................................................................................................................................................. 1
Input ........................................................................................................................................................ 2
Extra Comments...................................................................................................................................... 2
Winter and summer ................................................................................................................................. 2
THE WORKSHEETS................................................................................................................................... 3
4.1.
WORKSHEET ‘ROOM SPECIFICATIONS’..................................................................................................... 3
Input method ........................................................................................................................................... 3
Results ..................................................................................................................................................... 4
4.2.
WORKSHEET ‘HEAT LOSS’ (WINTER SITUATION)...................................................................................... 5
Explanation ............................................................................................................................................. 5
Input method ........................................................................................................................................... 5
Results ..................................................................................................................................................... 6
Explanation ............................................................................................................................................. 7
Input method ........................................................................................................................................... 8
Results ................................................................................................................................................... 11
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Guideline for building services calculations – heat loads
1. Introduction
This guideline provides background information about the use of the program Heat Load. This
program is meant for the student to develop a notion about calculations concerning the HVAC
services. These calculations provide a basis for a proper selection of heating/ cooling systems and
indicate the order of magnitude of heating and cooling loads. The program itself is meant as an
education tool only; it is not a design tool.
The data required for filling in the spreadsheet can be found in the book (in Dutch):
• Klimaatinstallaties, Integratie van gebouw en installaties
Ing. T.A.J. Schalkoort en Prof. Ir. P.G. Luscuere (uitgave 2004)
Some cells in the spreadsheet refer to this book, or the website of the Building Services chair.
2. Start up of the program
⇒ Log in on the network with your username and password.
⇒ Download the spreadsheet-file.
⇒ Make a separate copy for every room that you are about to calculate, and give a different name to
every saved file (e.g. Kabinet SW; Kabinet NO; Library; etc.).
⇒ Open the (or one of the) saved file(s).
⇒ Start with the worksheet ‘Room specifications’.
3. The Program
•
Structure
Sheet
‘Room specifications’
Sheet
‘Heat loss’
Sheet
‘Cooling load’
The program is built up by three interactive worksheets; as shown schematically in the figure below.
The value input the worksheet ‘Room specifications’ (dimensions of the room, temperatures and
orientations) will be used for the calculations of the heat loss and the cooling load.
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
•
Input
Values are requested in the cells with a bold border.
N.B.: The numbers used in the examples are for illustration only and can never simply be copied!
•
Extra Comments
In some of the cells you can see a little red triangle. If you place the cursor of the mouse on this cell
you can see the extra comments box pop up. This box provides extra information or explanation about
the requested input.
With air heating
Volumetric airflow required for heating
with high supply ∆t toe,afv <
20 K
with low supply ∆t toe,afv <
40 K
•
This "∆t" is the difference
between the supply and
exhaust
temperature
of
w / (ρ c ∆t)=
qv,Φw =Φ
the recirculated air used
qv,Φw
=Φwthe/ room
(ρ c ∆t)=
for
heating
0.11 m3/s
406 m3/h
0.06 m3/s
203 m3/h
Winter and summer
The calculation of the heat loss should be made for a winter situation. During winter it is colder
outside than inside, so the heat transfer will take place from inside to outside.
During summer there will be a heat transfer from outside inwards. This external load together with
the internal load (by people, lighting and equipment) is required to define how much cooling is
needed in a room during summer. The sum of internal and external loads is called the rough cooling
load.
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
4. The worksheets
4.1. Worksheet ‘Room specifications’
•
Input method
On this worksheet the following data are required:
• Room and window dimensions
• Façade orientation(s)
Room dimensions and orientation
Net height [m]
2.70 m
Gross height (floor-floor) [m]
3.30 m
.60 m
Window width [m]
.90 m
depth
facade
Window height [m]
please
Fill in
3.60 m
Facade/front side width [m]
Right side
W
winter
Temperatures
Design temperature, ti [°C]
zomer
22 C
25 C
Left side
Adjacent room temperatures, if applicable
Right side[°C] ]
-7 C
28 C
Front side
-7 C
28 C
-7 C
28 C
15 C
25 C
o
C]
Below (floor? outside?)
[C°
Ceiling/roof
above
heigth
Back side [°C]
Back side
28 C
Front side
25 C
-7 C
facade
22 C
o
Left side [°C]
above
width
Front side
Orientation (N,NE,NW,S,SE,SW,E,W)
Back side
5.40 m
Room depth [m]
Other windows, if present (Outside windows only!)
right
Right side window height [m]
.0 m
Right side window width[m]
.0 m
Orientation (N,NE,NW,S,SE,SW,E,W)
.60 m
Back side window height [m]
back
.90 m
Left side window width[m]
orientation(N,NE,NW,S,SE,SW,E,W)
Z
1.90 m
Back side window width [m]
Orientation (N,NE,NW,S,SE,SW,E,W)
.90 m
O
Roof window length [m]
roof
.0 m
Roof window width[m]
orientation (N,NE,NW,S,SE,SW,E,W)
below
N
Left side window height [m]
left
floor
.0 m
Horiz.
Please be aware of the following during input:
• Only numbers are supposed to be filled in. (Filling in the units leads to errors)
• Decimals have to be divided with dots in English versions of Excel.
• If there are any other windows, then these have to be taken into account as well. If not, then please
fill in 0 in those fields. The orientations have to be filled in for all of the façades.
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
•
Results
In this worksheet, the following values are calculated:
• Component surface areas (e.g. walls, windows, etc.)
• Room volume
• Glass percentage (as % of the wall)
• Differences in temperature in relation to adjacent rooms and outdoor surroundings.
These values will be inserted in the spreadsheets ‘Heat loss’ and ‘Cooling load’.
⇒ You can proceed now to worksheet ‘Heat Loss’
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
4.2. Worksheet ‘Heat loss’ (winter situation)
•
Explanation
In this worksheet the need for heat in winter in a room will be calculated based upon general values of
heat loss caused by transmission and outdoor air flow (infiltration or natural ventilation). The heating
up allowance Φheat is taken into account as well (50% of the loss by transmission).
The heat loss by transmission is calculated taking in consideration that heat transfer occurs between
rooms because of a temperature difference (∆t) between the inner side and the outer side of a surface
(wall, window, roof). Furthermore, the surface areas (A) as well as the overall heat transfer coefficient
(U-value) are of influence for this heat transfer. The U-value is a property that defines how much heat
can be transferred through a component (like a concrete wall with cavity and thermal insulation). The
U-values are adjusted by a correction factor (e), to account for heat transfer between walls and the
surrounding air.
Heat loss caused by outside air supply is a result of convective heat transfer, which occurs when
warm air in the room mixes with the cold air that has come in via ventilation or infiltration. The physical
properties of the air are assumed to be constant. The heat capacity of air (ρ • c) states the amount of
heat that is needed to increase 1 m3 of air by 1 degree in temperature. The heat loss by outside air
supply is thus determined by the quantity of outside air (qv,inf/vent) and by the difference in temperature
(∆tin, out) between indoor and outdoor air.
For more details about the calculations on heat loss please refer to the slideshows on the website.
Show; ‘Thermal loads and comfort’, and ‘Nature of heating loads’.
In Dutch: De procedures voor warmteverliesberekeningen zijn uitgelegd in paragraaf 6.2 van het
diktaat en samengevat in bijlage 4.
•
Input method
Heat loss by transmission
The overall heat transfer coefficient (U value) should be typed in for all room components (walls,
ceilings, etc.) Please refer to the website; Tabels, ‘Eigenschappen zonwering/ beglazing’ for typical Uvalues for glass.
In Dutch: Paragraaf 6.2.7 van het diktaat, voor de U-waarden en 6.2.1 voor de berekeningsformules.
You can calculate the U-value yourself as well:
U = 1/R
R = Ri + Σ d/λ + Rsp + Re
[m2 * K/W]
Ri = heat transfer coefficient on the inside ≈ 0,13 m2 * K/W
Re = heat transfer coefficient on the outside ≈ 0,04 m2 * K/W
λ = thermal conduction coefficient [W/mK], check out the bouwfysisch tabellarium
Rsp = heat resistance of an air space ≈ 0,2 m2 * K/W
The values of e, A and ∆t will be filled in automatically.
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
transmission
e
U
A
∆t
[-]
[W/m2 K]
[m2]
[K]
Window (front side
Parapet (front side)
Roof or ceiling
floor
Wall, right side
Wall left side
Wall, back side
1.15
1.02
1.02
1.05
1.09
1.02
1.02
3.2
0.4
0.4
1.2
2
0.4
0.4
0.54
11.34
19.44
19.44
17.82
17.28
10.17
Φtr
[W]
29
29
29
7
0
29
29
57
134
229
172
0
204
120
......through other windows, if present
Window, right side
1.00
0
0
0
Window, left side
1.15
3.2
0.54
29
57
Window, back side
1.15
3.2
1.71
29
182
Window, roof/ceiling
1.00
0
29
Σ(Φtr)
0
1155 W
Φopw = 0.5 x Φtr
Please fill in
577 W
Heat loss by outside air supply
The amount of air that infiltrates through cracks and other openings is put in as qv,inf/vent for
infiltration.
For commercial buildings with natural ventilation, the need for fresh air has to be taken into account
as well as the heat loss caused by that ventilation. This has to be filled in as qv,inf/vent for ventilation.
Please fill in
Access of outside air
infiltration
ventilation
qv,inf/vent
ρ
c
∆tIn, out
Φinf,vent
[m3/s]
[kg/m3]
[J/kg K]
[K]
[J/s] = [W]
.0166
.028
1.2
1.2
1000
1000
29
29
578
974
Max(Φ inf)
974 W
To find the formula for the calculation of qv please refer to slide 6 in show; ‘Nature of heating loads’.
(Building Services website) In Dutch: Paragraaf 6.2.5 van het diktaat behandelt de formule voor de
berekening van qv.
Be aware of the different units which are being used; this can cause confusion.
If necessary, the values will have to be converted to m3/s.
•
Results
The program calculates the following, using the filled-in values:
•
Rough heat loss. The rough heat loss is determined by transmission, heating up allowance and
outside air supply.
• Characteristic numbers for building services (specific heat loss and infiltration/ ventilation notes).
Based upon these numbers, the choice of the system of the required service machines is defined.
• At air heating (convection through the air) the needed amount of air and the circulation factor
belonging to it.
• Percentage of the total heat loss for every building component.
• System selection
Several systems are discussed in the following slide shows on the Building Services website: ‘Water
and air based systems’ and ‘Air handling systems’. In Dutch: Paragraaf 4.5 en 4.6.
⇒ You can proceed now to worksheet ‘Cooling load’
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
4.3. Worksheet ‘Cooling load’ (summer situation)
•
Explanation
The required cooling capacity of the cooling equipments is determined by the maximum simultaneous
need for cooling in one or more rooms.
In this worksheet the need for “coldness”, called cooling load further on, of a room is calculated based
upon the internal and external load.
Internal load
The heat produced by people, lighting and equipment defines the internal load. To get the internal
load, the number of people present has to be multiplied by the heat production per person. The heat
production depends on the level of activity of people. Heat production by lighting and equipment has
to be input per unit of floor area, thus in W/m2.
External load
In order to define the external load, heat gains via the façade are taken into account, as a result of
solar radiation (via glass), transmission, solar load via closed components and infiltration. The solar
radiation via (outside) windows has the largest influence on the magnitude of the external load.
The contribution of the cooling load as a result of the solar radiation through a window depends on the
position of the sun with respect to that façade. This means that the time of the day when the solar
radiation is at its maximum depends on the orientation of a given façade. (Refer to table: ‘Convective
heat qconv as a result of solar radiation’ on the Building Services website, in Dutch: tabel 30 in het
diktaat). In rooms with windows in more than one façade, the solar radiation heat gain through outside
windows (Φz,gl), has to be calculated for that time of the day when the maximum load occurs, for every
façade orientation where windows are present. Subsequently, only the largest values of these
maximum loads will be taken as input for Φz,gl.
The values in mentioned table for convective heat gains from solar load (qconv) take into account the
heat storage capacity of the walls, floor and ceiling. (Effective Thermal Mass) What qconv indicates is
not the incident solar radiation, but rather the part of the thermal energy that is being transferred
through convection to the room air.
We assume the following:
– Part of the heat which enters the room as radiation is absorbed in walls, floor and ceiling;
subsequently,
– Part will be taken up by the floor and the ceiling through conduction and,
– Part will be given off to the air in the room as through of convection.
Apart from qconv one should also consider the awnings factor (z), the glass area (Awindow), the ZTAvalue of the glass/sunshade combination and the correction factor (fd). For rooms with windows facing
more than one orientation, td is used as a correction factor to account for the fact that qconv values are
not maximum for all orientations at a given time of the day. By multiplying qconv values by appropriate
td values, for the required orientations, a designer can estimate the total solar heat gain for a room at a
given time of the day.
• The cooling load as a result of transmission through outside windows is defined by the U value of
the glass surface, and by the temperature difference in between indoor and outdoor air (∆tin, out).
• The solar load via outside walls and the roof is defined by the absorption coefficient of solar
radiation (a) – taken as 0,7, – the internal areas of outside walls and roof (A), if present, and the
incident solar radiation (qw).
• The cooling load by outside air supply is defined by qv,inf/vent (refer to slide show :’Nature of cooling
loads’ on the Building Services website, in Dutch: paragraaf 6.3.1 in het diktaat) and the difference
in temperature between indoor and outdoor air.
The procedures concerning the cooling load calculation are explained in the slideshows on cooling at
the Building Services Website. In Dutch: Zie het diktaat paragraaf 6.3 en de samenvatting in bijlage 5.
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
•
Input method
Internal load
The internal load consists of the heat given off by people (Φp), lighting (Φl) and equipment (Φa). These
numbers have got to be filled in.
Φp
Heat load people,
qp
Φp
[W]
[W]
2
Please fill in
Φl
Φa
Heat load lighting,
Heat load equipment,
p
[-]
100
200
Avloer
q
Φ
[m2]
[W/m2]
[W]
19.44
19.44
Internal load,
Φi
5
10
97
194
Φi=Φp+Φl+Φa
492 W
External load
The external load consists of solar radiation and transmission through outside windows (Φz,gl en
Φtr,gl), solar radiation through outside walls (Φz,w) and infiltration through cracks and other openings in
the facade (Φinf).
As for the solar radiation through outside windows (Φz,gl), in the case of rooms with windows
facing several orientations, calculations have to be performed for various times of the day. For every
window orientation Φz,gl has to be calculated for a different time of the day, and the maximum values
should be multiplied by the fd factor. (Please refer to the comments behind cells E18 and J17 in the
worksheet ‘cooling load’).
orientaation
Time of
the day
Sun radiation, OUTSIDE windows
[h]
Window, front side (facade)
Outside window, right side
Outside window, left side
Outside window, back side
Outside window, roof
W
16
N
16
S
16
E
16
Horiz. 16
A
z
[-]
1.00
1.00
1.00
window
[m2]
0.54
0
0.54
1.71
0
ZTA
qconv
fd
Φz,gl
[-]
[W/m2]
[-]
[W]
0.70
470
1.00
0.70
0.70
400
470
0.80
0.50
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
178
0
121
281
0
Σ(Φz,gl)
580 W
Max(Φz,gl)
709 W
Page 8
Guideline for building services calculations – heat loads
Solar radiation calculation for various times of the day
-rooms with windows facing more than one
orientation-
qconv
fd
Φz,gl
[m2]
[-]
[W/m2]
[-]
[W]
0.54
0.70
470
0.00
0
0.00
0
0
1.00
0.54
0.70
400
0
1.00
1.71
0.70
470
Horiz. 0
0.00
0
0.00
0
Front side
W
Right side
N
Left side
S
E
Back side
roof
Time of
the day
orientation
ZTA
z
Aglass
[h]
[-]
0
1.00
0
1.00
0
0
0
0
W
Σ(Φz,gl)
Time of
the day
orientation
Fill in, if necessary
z
Aglass
ZTA
qconv
fd
Φz,gl
[h]
[-]
[m2]
[-]
[W/m2]
[-]
[W]
0.54
0.70
470
Front side
W
13
1.00
Right side
N
13
0.00
0
0.00
0
Left side
S
13
1.00
0.54
0.70
400
Back side
E
13
1.00
1.71
0.70
470
Horiz. 13
0.00
0
0.00
0
roof
1.00
0.60
Time of
the day
orientation
Σ(Φz,gl)
124
0
151
338
0
613 W
z
Aglass
ZTA
qconv
fd
Φz,gl
[h]
[-]
[m2]
[-]
[W/m2]
[-]
[W]
Front side
W
9
1.00
0.54
0.70
470
Right side
N
9
0.00
0
0.00
0
Left side
S
9
1.00
0.54
0.70
400
Back side
E
9
1.00
1.71
0.70
470
Horiz. 9
0.00
0
0.00
0
roof
0.70
0.40
0.50
1.00
orientation
Time of
the dayt
Σ(Φz,gl)
71
0
76
563
0
709 W
[h]
[-]
[m2]
[-]
[W/m2]
Front side
W
0
1.00
0.54
0.70
470
0
Right side
N
0
0.00
0
0.00
0
Left side
S
0
1.00
0.54
0.70
400
Back side
E
0
1.00
1.71
0.70
470
0.00
0
0.00
0
0
0
0
0
W
roof
Horiz.
z
Aglass
ZTA
qconv
fd
Φz,gl
[-]
[W]
1.00
Σ(Φz,gl)
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
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Guideline for building services calculations – heat loads
The input of the numbers concerning transmission via windows, solar load via closed components and
infiltration is shown in the figure below, as an example.
Transmission OUTSIDE windows
Uglass
Aglass
∆tIn, out
Φtr,gl
[W/m2 K]
[m2]
[K]
[W]
Window, front side (facade)
Window right side
Window,left side
Window, back side
Window, roof
3.2
0.54
0
0.54
1.71
0
3.2
3.2
orientation
a
[-]
Solar load via OUTSIDE walls and roof
Parapet (front side)
Roo
Outside walls, right side
Outside walls, left side
Outside walls, back side
0.7
0.7
0.7
0.7
0.7
W
Horiz.
N
S
E
Access of outside air
infiltratio
3
3
3
3
3
5
0
5
16
0
Σ(Φtr,gl)
27 W
A
qw
Φz,w
[m2]
[W/m2]
[W]
9.18
19.44
14.58
14.04
8.01
13.7
-3.9
0
11.2
7
88
-53
0
110
39
Σ(Φz,w)
184 W
qv,inf
ρ
c
∆tIn, out
Φinf
[m3/s]
[kg/m3]
[J/kg K]
[K]
[J/s] = [W]
.0044
1.2
1000
3
Φinf
16
16 W
The following values have to be filled in as well:
• the difference in temperature ∆t supply, exhaust between supply and exhaust air in K (In Dutch: zie
paragraaf 4.4.10)
• a = absorption coefficient for solar radiation. The absorption coefficient has a minimum of 0,05 for
polished metals and a maximum of 0,95 for rough concrete surfaces. Because the solar radiation,
which enters the room through closed walls or roofs, is relatively little, it will not be a great fault
when you calculate with an average coefficient of 0,7. Φz,w can therefore be neglected as well
Please fill in ∆t supply, exhaust
Characteristic numbers – building services:
Specific cooling load
Φk,spec
= Φk / Afloor =
ninf =(qv,inf * 3600 / V =
Infiltration factor
73 W/m2
0.30 Times/hour
Needed amount of air for cooling
Quantity of cooled air ∆t supply, exhaust =
Needed circulation factor for cooling
Circulation factor for cooling
8K
qv,Φk = Φk / (ρ c ∆t)=
ncircul =(qv,Φk * 3600 / V =
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
0.15 m3/s
10.2 Times/hour
Page 10
Guideline for building services calculations – heat loads
•
Results
The program calculates the following, using the input values:
•
•
Rough cooling load.
Specific cooling load and infiltration/ventilation rates. Based upon these numbers a choice can be
made for the needed building services.
• For mechanical cooling: the required amount of air and the corresponding circulation rate.
• For natural ventilation: the required amount of outside air for cooling and the corresponding
ventilation rate.
• Percentage of the total cooling load through every component.
• System selection
System selection for cooling can be found in the following slide shows on the Building Services
website: ‘System selection for cooling’. In Dutch: Paragraaf 4.4 en 4.6 van het diktaat.
Education calculation tool for building services, TU Delft, Faculty of Architecture, 2002-2006
Page 11