Air Conditioning Design Strategy (CH2 design report)

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Air Conditioning Design Strategy (CH2 design report)

Transcript Of Air Conditioning Design Strategy (CH2 design report)

Melbourne City Council (CH2)
Air Conditioning Design Strategy
Prepared for: Melbourne City Council
Prepared by: Advanced Environmental Concepts Pty Ltd ACN 075 117 243 Level 1, 41 McLaren Street North Sydney NSW 2060
design advice passive systems design analysis low energy services May 03 AESY820000\0\2\SFT30503

Air Conditioning Design Strategy

Executive Summary

EXECUTIVE SUMMARY
This report has been prepared by Advanced Environmental Concepts as part of the design process for the new Melbourne City Council (MCC) offices which recognises the increasing concern for the environment through adopting Ecologically Sustainable Development (ESD) practices.
A green building is a sustainable and healthy building for its occupants and the environment. An important aspect in the design of green buildings is energy usage which affects carbon emissions. Carbon emissions are affected by the energy consumed by the base building (central services and common areas) and its tenants.
A building’s air conditioning system is typically responsible for around 50% of the base building’s energy consumption. The other 50% typically includes other services such as common area lighting, domestic hot water, lifts, etc. As such, any reduction in air conditioning energy consumption or efficient energy utilisation will offer significant savings in total building energy consumption and carbon emissions.
In response to the above, this report will examine the air conditioning system to be adopted by Melbourne City Council House through the separate analysis and assessment of initiatives and their effects on the air conditioning system
A base model will be used to represent a standard air conditioning system, and through comparative analysis, initiatives will be assessed. Initiatives include the use of night purging, displacement air flow, chilled ceilings/beams, 100% fresh air intake, phase change materials, and a co-generation plant. Analysis will mainly include the building’s energy consumption, energy utilisation and carbon emission reduction. All models will also be compared to a 4.5 star Australian Building Greenhouse Rated building.
It is recommended that, based on the results of this report, that night purging, displacement ventilation, chilled ceilings/beams, 100% fresh air intake, phase change materials and a co-generation plant be adopted to significantly contribute to the health of occupants, the reduction of carbon dioxide emissions and reduce energy consumption of the building.
The use of all these initiatives will reduce carbon emissions to 44% of a 4.5 star Australian Building Greenhouse Rated building. This is expected to reduce even further with the adoption of LCD flat screen monitors which reduce cooling loads by 12% and reduce the building’s energy consumption.

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TABLE OF CONTENTS
EXECUTIVE SUMMARY TABLE OF CONTENTS LIST OF FIGURES 1 INTRODUCTION 2 APPROACH
2.1 Models 2.2 Zones 2.3 Building Loads 2.4 Heating and Cooling Requirements
3 RESULTS
3.1 Base Model 3.2 Night Purge Model 3.3 Displacement Ventilation Model 3.4 Chilled Ceilings Model 3.5 Chilled Ceilings with 100% Fresh Air Intake 3.6 Phase Change Materials (PCMs) 3.7 Co-generation Plant 3.8 Model Comparisons
3.8.1 Energy consumption 3.8.2 Carbon emissions
4 CONCLUSIONS AND RECOMMENDATIONS

Date Revision and Status Author Project Team Leader

7 May 2003 Final Su-fern Tan Mark Cummins

Table of Contents
I II III 4 5
5 7 7 8
10
10 11 13 14 17 18 20 22 22 23
24

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list of Figures

LIST OF FIGURES
Figure 1. The 3D TAS Model used for analysis....................................................................................... 5 Figure 2. Mixed air distribution in a VAV system................................................................................... 5 Figure 3. Displacement ventilation air layering effect ........................................................................ 6 Figure 4. Chilled ceilings radiant cooling effects ................................................................................ 6 Figure 5. Example of a phase change (PCM) module. Source PCI. ................................................ 6 Figure 6. Zones in floor plan ................................................................................................................... 7 Figure 7. Hourly building loads............................................................................................................... 7 Figure 8. Monthly breakdown of heating and cooling requirements of total building ................... 8 Figure 9. Zone breakdown of heating and cooling requirements .................................................... 9 Figure 10. Zone cooling percentage breakdown............................................................................... 9 Figure 11. VAV system mixed air distribution...................................................................................... 10 Figure 12. Annual energy load profile for the base model .............................................................. 10 Figure 13. Estimated annual energy consumption for base model ................................................ 11 Figure 14. Estimated annual energy load profile for the night purge model ................................. 12 Figure 15. Estimated annual energy consumption for night purge model..................................... 12 Figure 16. Displacement ventilation effects....................................................................................... 13 Figure 17. Estimated annual energy load profile for the displacement ventilation model .......... 13 Figure 18. Estimated annual energy consumption for displacement model ................................. 14 Figure 19. Example of chilled ceiling panel. Source BSEE................................................................. 15 Figure 20. Estimated annual energy load profile for chilled ceiling model .................................... 15 Figure 21. Estimated annual energy consumption for chilled ceiling model ................................. 16 Figure 22. Estimated annual energy load profile for 100% fresh air model..................................... 17 Figure 23. Estimated annual energy consumption for 100% fresh air model.................................. 18 Figure 24. Basic Phase Change Material (PCM) schematic ............................................................ 19 Figure 25. Estimated annual energy load profile for the PCM model............................................. 19 Figure 26. Estimated annual energy consumption for PCM model................................................ 20 Figure 27. Gas fired co-generation plant at Macquarie University, NSW. Source SEDA................ 20 Figure 28. Estimated annual energy load profile for co-generation model................................... 21 Figure 29. Estimated annual energy consumption for co-generation model ................................ 21 Figure 30. Energy comparison of all models ...................................................................................... 22 Figure 31. Carbon emission comparison of all models ..................................................................... 23 Figure 32. Chilled ceiling panels in Cannons, Covent Garden. Source SAS International............ 24 Figure 33. Ventilation stacks, Solar Energy Research Facility, Colorado. Source NREL. ................ 25

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introduction

1 INTRODUCTION
This report presents the approach, results, conclusions and recommendations for the analysis carried out to propose a best practice air conditioning system with efficient energy consumption and reduced greenhouse gas emissions.
The Approach section will discuss how we begin the study by first examining the loads on the building when it is complete and occupied. This provides a guide to the heating or cooling loads required to be met throughout the year, to maintain air and temperature levels for comfort. Each model built for analysis will also be discussed in this section.
The Results and Discussion section will show the results and analysis of the modelling which will form the basis of our Conclusions and Recommendations section. The different systems modelled will be rated based on their energy consumption, and carbon dioxide emissions compared to a 4.5 star rated building.

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approach

2 APPROACH
Thermal Analysis Software (TAS) was used to create an accurate three-dimensional thermal model to assess the performance of the building. The model uses current building design, and performs dynamic building simulation and calculations from which an accurate analysis can be undertaken.

Figure 1. The 3D TAS Model used for analysis
2.1 Models
The first model built represents the MCC offices using a conventional, good practice, variable air volume (VAV) air conditioning system which relies on the mixing of room air. Such a system is typical for most grade ‘A’ buildings within Australia. This model will act as a base model for our analysis.

Figure 2. Mixed air distribution in a VAV system
The second model represents the MCC offices using the previously modelled VAV system with night purging ventilation. The night purge system occurs when windows automatically open at night if the outside air is cool enough to naturally cool down the building via cross ventilation. This model will show if there are any benefits using a night purge strategy.

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The third model uses the second MCC model and adds displacement air flow to the building. Displacement air flow allows air at different temperatures to move from an entry point ie cold air from supply air floor grills, to an exit point ie exhaust air slots in the ceiling. This means that supply and exhaust air does not keep mixing but instead follows a one way flow path. The third model shows if there is a benefit in a displacement air flow strategy.

Figure 3. Displacement ventilation air layering effect
The fourth model makes one change to the third model by adopting a chilled ceiling/beam system for space cooling, and thus replaces the VAV system. The fourth model was created to show if there are benefits to a chilled ceiling air conditioning system.

Figure 4. Chilled ceilings radiant cooling effects
The fifth model uses phase change materials (PCMs) in conjunction with shower/cooling towers to provide cooling chilled ceilings/beams instead of using electric chillers. This model will show the PCM’s contribution to the reduction in electricity consumption.

Figure 5. Example of a phase change (PCM) module. Source PCI.
The sixth and final model uses waste heat from a gas powered co-generation plant to provide a significant amount of energy required for heating and/or cooling fresh air entering the space. The final model will show if there are any benefits in energy consumption by using a co-generation plant.

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2.2 Zones
For each model, the floor plan has been divided into five zones which each have different heating and cooling requirements. The zones are
North perimeter

West perimeter

Centre

East perimeter

Figure 6. Zones in floor plan

South perimeter

2.3 Building Loads
Building loads determine the heating and cooling requirements of a building and come from sources such as occupants, equipment, lighting and the sun.
The following graph shows building loads over a 24 hour period on the new MCC office building and solar loads for typical summer, mid-season and winter days.

kWh

Hourly Loads on Building
160 140 120 100
80 60 40 20
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
hour Figure 7. Hourly building loads

Lighting Occupants Equipment Summer Solar Mid-season Solar Winter Solar

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For office buildings like the new MCC offices, lighting, occupant and equipment loads are constant throughout the year on working days. Solar loads will vary daily and depend on seasonal and weather conditions.
The heating and cooling requirements of a building depend on the loads placed on that building.

2.4 Heating and Cooling Requirements
The amount of energy which must be supplied or removed by the air conditioning system in order to maintain comfort are called the heating and cooling loads.

The following graph shows the monthly heating and cooling loads for the whole building. These results assume there is no night purge occurring and like all models, the air conditioning system operates from 7am until 6pm.

Monthly Heating and Cooling Loads

HEATING LOADS
jan feb mar apr may jun jul aug sep oct nov dec

COOLING LOADS

-200 -100 Note: Scale

0

0

(kWh)

10000 20000 30000 40000 50000 60000 70000 80000 90000

Figure 8. Monthly breakdown of heating and cooling requirements of total building

It is apparent that the building will require very little heating during colder months, and a significantly large amount of cooling throughout the year due to constant solar and internal load gains.
Heating and cooling requirements can also be viewed on a per zone basis which facilitates efficient air conditioning design. For example, the centre zone will have totally different cooling requirements to the west perimeter and trying to control the temperature in both of these zones from the same air supply is neither efficient nor very effective.

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Zone Heating and Cooling Requirements

(kWh )

200000 180000 160000 140000 120000 100000
80000 60000 40000 20000
0
0 -50 -100

Note: Scale

East Perim

COOLING LOADS
North Perim South Perim West Perim Centre Zone
HEATING LOADS

Figure 9. Zone breakdown of heating and cooling requirements

The building is dominated by cooling loads and not heating loads. Furthermore, we can see that the cooling load on the building is largely driven by the centre zone.
The next graph shows the proportion of cooling requirements for the building in each zone.
Annual Zone Cooling % Breakdown

2% 7% 10% 3%
78%

East Perim North Perim South Perim West Perim Centre Zone

Figure 10. Zone cooling percentage breakdown

The following analysis will look at the options adopted for air conditioning and examine their contribution to the reduction in energy consumption whilst still satisfying heating and cooling requirements.

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BuildingModelHeatingCooling RequirementsEnergy Consumption