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Prof. Dr.-Ing. Uwe Franzke ILK Dresden Cooling Loads – the new standard VDI 2078 useable for Optimization of Buildings and for Determination of the Requirements of the Technical Systems
20.05.2014 VDI Society Civil Engineering and Building Services 1 /
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New Cooling Load Calculation Rule VDI 2078 2
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Structure
1. Basics of VDI 2078 2. New features of the algorithms of VDI 2078 3. Description of the master room 4. Using the algorithm for the approval according to DIN 4108-2 5. Description of influences of the technical system on the cooling load 6. Summary
New Cooling Load Calculation Rule VDI 2078 3
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Overview about the VDI-Guidelines
4
Calculation of transient thermal response of rooms and buildings
Modelling of rooms
VDI 6007 - 1 VDI 6007 - 2 VDI 6007 - 3
Calculation of transient thermal response of rooms and buildings
Modelling of
windows
Calculation of transient thermal response of rooms and buildings
Modelling of solar
radiation
Cooling Load Calculation of Air-conditioned Rooms
VDI 2078
New Cooling Load Calculation Rule VDI 2078
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Physical approach
New Cooling Load Calculation Rule VDI 2078 5
∂ϑ∂
λρ
∂ ϑ∂
( , ) ² ( , )²
t xt c
t xx
=⋅
⋅
∂∂
∂∂
u t xt R C
u t xx
( , )' '
² ( , )²
= ⋅1
Differential equation of the heat conduction
Differential equation of an idealized electrical conductor
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2-Capacitor-Model
New Cooling Load Calculation Rule VDI 2078 6
Source: Zimmermann
Ambient Temperature Exterior wall Room Air Interior wall
C – Capacitor R - Resistance
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Conclusions
New Cooling Load Calculation Rule VDI 2078 7
The algorithms of the 2-capacitor-model permit a
calculation in one hour steps without an effortful storage of
the past history.
Wall set is included correctly with all layers in its efficiency
so that an assessment of the style is possible with that.
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8
Definition of cooling load according to ASHRAE
Cooling Load VDI 2078 (1996)
(SWING = 0, Temperatur = const)
New Cooling Load Calculation Rule VDI 2078
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9
HVAC EQUIPMENT incl. Cooling Panel
VARIABLE HEAT STORAGE
HEAT GAIN
COOLING LOAD
RADIATION
CONVECTION
CONVECTION (W. TIME DELAY)
+/- SWING
HEAT EXTRACTION
RADIATION CONVECTION
CONTROL
2-CAPACITY-MODEL VDI 2078 (new)
(SWING, Temperatur = variable)
New Cooling Load Calculation Rule VDI 2078
Definition of cooling load according to ASHRAE
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New Features
• Cooling Design Period • It’s possible to use the algorithm to prove the thermal protection
and energy economy in buildings according to DIN 4108 - Part 2 • Calculation of the cooling load as well as the hourly energy
demand • Integration of different technical HVAC-systems (air- and water
based) • Evaluation of free ventilation by opened windows
New Cooling Load Calculation Rule VDI 2078 10
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Cooling Design Period / Cooling Design Day
11
The Design Period contains temporal overlappings of climate parameters and use; standardized sequence of operations; you calculate under aperiodic gains in the non-steady state.
New
The Design Period contains only days with identical boundaries; you calculate under periodic gains in the steady state. Ti
l now
Cooling Design Period = Design Period for the Calculation of the Cooling Load under defined Boundary Conditions, which ends with Cooling Design Day (CDD).
New Cooling Load Calculation Rule VDI 2078
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Office Room
New Cooling Load Calculation Rule VDI 2078 12
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Office Room
New Cooling Load Calculation Rule VDI 2078 13
Orientation: SW
Exterior wall: U=0.14 W/m² K
Window: U=1.50 W/m² K
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New Cooling Load Calculation Rule VDI 2078 14
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New Cooling Load Calculation Rule VDI 2078 15
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Outside Sun Protection
New Cooling Load Calculation Rule VDI 2078 16
Outside Sun screen will be closed down up 200 W/m²
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Outside Sun screen
New Cooling Load Calculation Rule VDI 2078 17
Total energy transmittance g
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DIN 4108 - Part 2
Aim of this guideline: To check the protection of the building against solar radiation and thermal strength For non-residential buildings: Internal loads: 144 Wh/(m² d) Operation time: From Monday to Friday between 7 am and 6 pm Ventilation during operation: Ventilation during non-operation time:
New Cooling Load Calculation Rule VDI 2078 18
⋅=h1
VA4n G
=h10.24n
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Requirements
New Cooling Load Calculation Rule VDI 2078 19
During a whole year it‘s not allowed to accept more than 500 Kh/a in the range of non-residential buildings.
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Results
New Cooling Load Calculation Rule VDI 2078 20
514 500
0
100
200
300
400
500
600
Tem
pera
ture
s ab
ove
26 °C
[Kh/
a]
VDI-Headquarters DIN 4108-2
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Results
operatives temperatures numbers of overheating
°C h/a
26 337
28 94
30 14
New Cooling Load Calculation Rule VDI 2078 21
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Cooling load calculation
Internal loads: Staff: 2 with 75 W per person Lighting: 6 W/m², 118 W PC‘s: 2 with 50 W per PC Cooling equipment: Thermal activated ceiling Ventilation systems with a supply temperature of 18 °C
New Cooling Load Calculation Rule VDI 2078 22
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Cooling load - CDP and CDD
New Cooling Load Calculation Rule VDI 2078 23
-1000,0
-900,0
-800,0
-700,0
-600,0
-500,0
-400,0
-300,0
-200,0
-100,0
0,0 0 20 40 60 80 100 120 140 160
cool
ing
load
[W]
time [h]
Specific cooling load: 42 W/m² Temperature swing: 24 °C ± 2K
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Annual energy demand
New Cooling Load Calculation Rule VDI 2078 24
-1000,0
-800,0
-600,0
-400,0
-200,0
0,0
200,0
400,0
600,0
800,0
1000,0 0 2000 4000 6000 8000 10000
cool
ing
load
[W]
time [h]
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Summary
• The cooling load calculation rule 2012 leads to a better consideration of the real storage behavior
• Usage of the fluctuation of the room temperature of at least 2 Kelvin
• Usage of the activated ceiling during the whole day • Usage of the Convection (air system) as add on during the
common operating time • Daylight-Simulation
New Cooling Load Calculation Rule VDI 2078 25