Cooling Load as per VDI 2078

 Overview

VDI 2078 contains two different calculating procedures: the short procedure and the dynamic procedure. The short cooling load calculation procedure as per VDI 2078 is performed by an interactive program with which the user can compute the cooling load of a room or building for predefined boundary conditions. Cooling load factors are used for computing in-room storage effects resulting from internal and external radiation loads, while the storage effects in the outside walls and roofs are computed on the basis of equivalent temperature differences.

Short Procedure

  • Clear registration of building structure by storey, level, and room; several users can take active part in the current project; database-oriented
  • Simple treatment thanks to fixed boundary conditions, such as constant room temperature, periodic internal and external loads, steady state, 24-hour operation of technical facilities, and constant sun protection factor of windows (no migrating shades)
  • Calculation of internal cooling load caused by persons, lighting, machines, material throughput and as a consequence of varying temperatures in neighbouring rooms
  • Calculation of external cooling load through outside walls and roofs, transmission and radiation through windows, and infiltration
  • Calculation of moist cooling load in g/h
  • Graphical display of cooling load over the course of a whole day
  • Generated report is clearly structured and easily comprehensible 

Dynamic Procedure

The Navigator is the central C.A.T.S. Windows application in which the building data, the location, and all required building components are defined in a project file. 
The program supports the calculation of projects outside the range of the VDI 2078 tables. This means that projects can be calculated all over the world. Spatial geometries can also be imported from the CAD. Relevant data is assigned to the respective room number directly in a dialogue.

The new C.A.T.S. cooling load calculator offers many new and comfortable inputting and outputting options that even exceed the requirements of the VDI 2078 guidelines. Not only that, but it also represents a solution that can easily be adapted to comply with the requirements of the new VDI 6007 guidelines.

A draft version of VDI 2078 is expected for the middle of the year 2008, which is expected to hive off the calculating process and refer it to VDI 6007. VDI 6007 in turns requires that all surfaces in a room have a layer structure, to make it possible to deduce individual storage behaviours. This will lead to an increase in workload and procurement activities on the part of the planners. It will be interesting to see whether the increased effort will be worthwhile in terms of enhanced precision.
Basically, only U-values and a few boundary parameters are needed for the C.A.T.S calculation; these are generally available from the structural engineer or architect. In the preliminary planning stages with an unknown wall structure, it is possible instead of U-values to use maximum values, as referred to in the legal provisions.
It is therefore a great advantage of the new calculation that the building components do not require any layer data, such as thickness, specific heat capacity, density, thermal conductivity, or layer sequence, etc.

Synchronisation with heating load and CAD extended
Not only is it possible to input data directly into the program, but room geometries can also be transferred from CAD. This saves the user time, and he can also use most of the data again if he needs to simultaneously calculate the heating load. This requires an extension of the data union between cooling load and heating load. Building components such as walls to neighbouring rooms can now be assigned different cooling load and heating load parameters in CAD. There is also the highly convenient option of incorporating complete load profiles, for example for lighting, persons, shade, etc., in CAD.

Load profiles


In each project there are areas which resemble each other in terms of their heating or cooling loads. By using specific load profiles, the data input requirements are considerably reduced. Variations can be calculated quickly and simply. All profiles can be set in all cases to all situations, 24 hours a day and 12 months in the year.

This applies to:

Sun protection
Shade
Persons
Lighting
Machines
Air flows
Cooling of building components (unregulated basic load cooling)
Controller characteristics (technical installation data)

Profiles can of course be saved globally and used in further projects.

Subdivision into zones
In addition to the standard division into rooms, storeys, and buildings, a further grouping is now available: zones. In these zones, the user can group individual rooms independently of storeys; he can also perform zone calculations and observations. This makes it possible to map the various conditions that prevail within a project. Keywords: south side/ north side, staircases.

 

Worldwide locations


The new program also enables the user to perform calculations outside the geographical zone of the VDI 2078 (Germany) tables. The following climatic data is currently incorporated:

Germany - complete 
Austria - complete
Switzerland - complete 
Italy - Rome 
Spain - Madrid 
France - Paris 
Netherlands - Amsterdam 
Russia - Moscow 
Greece - Athens 
Czech Republic - Prague 
Croatia - Zagreb 
Hungary - Budapest 
Poland - Warsaw 
China - Hong Kong
China - Peking 
Singapore
UAE - Dubai 
Vietnam - Saigon 
Cambodia - Phom Penh 
Saudi-Arabia - Jeddah 
India - Bangalore 
Australia - Sydney 
South Africa - Cape Town

Other world locations can be drawn up and incorporated upon request.

Input options
The new C.A.T.S. cooling load calculator offers many new ways of inputting data.

Particular reference must be made to the integration of air flows and building component cooling, such as cooling ceilings.

The stress from air flows can be given either statically with a fixed temperature or with respect to the outside temperature. Optionally, the external humidity can be set interactively to fixed daily values. 

When including a cooling ceiling in the calculation, it is possible to give both absolute and specific heat absorption.

Regarding "internal loads", personal heat emission is calculated in accordance with DIN ISO 7730. It is only necessary to input the number of persons and their degree of activity. For persons, the dry and wet loads are separated and then used automatically in the subsequent part of the program.
For lighting, it is possible to select single load recording or to use a global value per square metre.

Solar radiation can also be computed with a component inclination and albedo (short-term reflection factor) that deviates from the VDI 2078 guideline. Very light and very dark surfaces (e.g. due to water surfaces, forest, etc.) in the vicinity of the building component will result in an albedo that deviates from the standard value of 0.2.

The combined outside temperature is calculated taking into account the reflections in the terrestrial vicinity. This means that parking spaces, water surfaces and aluminium facades located opposite, with deviating emission values, can be taken into consideration.

External shade caused by buildings located opposite is calculated.

The shade surfaces (soffit, escape balcony) can also have an angle of inclination that is not 90°. Shade is also taken into account for non-transparent external building components.

Neighbouring room temperatures can either be determined statically or they can "oscillate" with adjustable references to outside or inside temperatures.

Regulating methods
Regulating methods have now been optimised and expanded. There are a number of regulation options that can be considered:

Regulating power output
Regulating volume flow
Regulating volume flow for a source-air system
Incoming air temperature regulation
Incoming air temperature regulation for a source-air system

In addition to room air temperature, it is possible to base measurements on operative temperature (i.e. felt temperature).
The regulation functions can be equipped with installation limit values. The program calculates the data required for output, volume flow or incoming air temperature relative to the selected type of computation.
The calculation of volume flow and incoming air temperature takes into account not only the dry load but also the wet load, and the required incoming air status is also computed. For this purpose, the external air humidity is incorporated in the room's humidity balance.

The relative room air moisture is derived from the humidity balance. For cooling ceilings, it is possible to check if the dew point has not been reached.

As regards power regulation, the regulated cooling and heating systems in a building component are inputted through the system's convective section.

 

Calculation and Simulations


The generated report has a consciously clear structure, as its aim is to help the user locate precisely the data he requires from the large amount available. The report of the C.A.T.S. cooling load program can be generated easily, using clear diagrams and graphs. All aspects of diagram presentation can be changed and the reaction values can also be incorporated. The user maintains control and retains a good overview; irregularities can be safely localised. The user can easily toggle between individual diagrams by month, without having to repeat the calculation.

Thermal comfort factor is becoming an increasingly important factor. The C.A.T.S. cooling load can determine the degree of sensed thermal comfort under all room conditions. It is then possible to localise deficits in thermal comfort and thereby minimise the percentage of unsatisfied persons (PPD value after Fanger).

Illustration of thermal comfort (below): it can be clearly seen that the percentage proportion of unsatisfied persons (PPD value) increases as soon as the temperature goes beyond the broad tolerance band (green).

To perform a simulation, there are a number of different calculation types that can be activated and deactivated, in order to recognise differences or to underline certain features. For example, the planner can decide not to include direct sun radiation in his calculations or to deactivate all inner loads. The system can be switched off to demonstrate the temperatures that would occur without the regulating system, for instance to provide an alternative demonstration of summer heat protection.

Detailed and well laid out: prints and reports
There are numerous reports that can be selected for securing and verifying the results of the computation. All diagrams that support it are displayed together with the report tables. All reports have a simple structure and contain brief legends in which abbreviations and terminology are explained.

According to requirements, room, zone, level or building reports can be produced. All reports can also be outputted as a PDF file.

The following reports are available:

  • All input data
  • Frequency with which current temperature is exceeded with reference to the outside temperature 
  • Frequency with which current temperature is exceeded with reference to the target inside temperature
  • List of rooms showing the hours and months in which the maximum values for cooling and heating load were attained.
  • Annual total cooling load and heating load for certain months and hours
  • Room load with all individual loads (action and reaction values) and temperatures in each hour and month
  • Simultaneous presentation of target and current values for cooling load and temperatures in the room, also showing action values
  • Total load with all individual loads (reaction values) in each hour and month
  • Total load with all individual loads (reaction values) in a selected hour of a month
  • PPD thermal comfort including personal warmth
  • Room conditions with incoming and outgoing air information in each hour and month

 

 

 

 

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