Prof. Dr.-Ing. Uwe Franzke ILK Dresden Cooling Loads … · Prof. Dr.-Ing. Uwe Franzke ILK Dresden Cooling Loads – the new standard VDI 2078 useable for Optimization of Buildings

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 /

New Cooling Load Calculation Rule VDI 2078 2

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


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


Modelling of

windows


Modelling of solar

radiation

Cooling Load Calculation of Air-conditioned Rooms

VDI 2078

New Cooling Load Calculation Rule VDI 2078

Physical approach


∂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

2-Capacitor-Model


Source: Zimmermann

Ambient Temperature Exterior wall Room Air Interior wall

C – Capacitor R - Resistance

Conclusions


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.

8

Definition of cooling load according to ASHRAE

Cooling Load VDI 2078 (1996)

(SWING = 0, Temperatur = const)


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)


Definition of cooling load according to ASHRAE

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


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).


Office Room


Office Room


Orientation: SW

Exterior wall: U=0.14 W/m² K

Window: U=1.50 W/m² K



Outside Sun Protection


Outside Sun screen will be closed down up 200 W/m²

Outside Sun screen


Total energy transmittance g

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:


⋅=h1

VA4n G

=h10.24n

Requirements


During a whole year it‘s not allowed to accept more than 500 Kh/a in the range of non-residential buildings.

Results


514 500

0

100

200

300

400

500

600

Tem

pera

ture

s ab

ove

26 °C

[Kh/

a]

VDI-Headquarters DIN 4108-2

Results

operatives temperatures numbers of overheating

°C h/a

26 337

28 94

30 14


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


Cooling load - CDP and CDD


-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

Annual energy demand


-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]

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


Documents

Prof. Dr.-Ing. Uwe Franzke ILK Dresden Cooling Loads … · Prof. Dr.-Ing. Uwe Franzke ILK Dresden Cooling Loads – the new standard VDI 2078 useable for Optimization of Buildings