Mechanical Ventilation and Air Conditioning Design

This assignment details the HVAC design for a level 2 office space in a mixed-use suburban development located in Maitland, NSW. The design adheres to Australian building codes and international standards, focusing on air conditioning and mechanical ventilation. The project includes detailed calculations for heat load using the Carrier method, considering factors like occupancy, lighting, and equipment. The design specifies air-cooled packaged air conditioning units, and the psychrometric chart is presented for summer conditions. Ductwork design is also covered, including the sizing of ducts for both the main system and toilet exhaust systems, referencing relevant Australian standards. The assignment also covers equipment selection, and the design allows for a factor of safety to balance the load, providing an overview of the entire HVAC system design process.

Office HVAC Design 1
OFFICE HVAC DESIGN
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Professor’s Name
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Office HVAC Design 2
HVAC Design
The HVAC design is as per Australian Local Building Codes as well as International
Standards. The scope of this assignment covers air conditioning and mechanical ventilation for
level 2 office floor for the proposed suburban mixed office development in Maitland NSW. The
physical site location is Latitude 320 44’ and 6m elevation above sea level.
Assumptions and design conditions
The conditioned space is occupied between 8.00 am and 6.00 pm, (10 hours) five days a
week. The air conditioning units are packaged type and air-cooled. Air-cooled type is
economical in terms of space requirements, pipework, equipment weight and cost (Harvey, and
Sillato 2019). The outdoor units will be located on the AC terrace on South-East end of the
building.
The design is for Summer conditions only as follows.
Design Condition Indoor Outdoor Control Tolerance
Summer 250C DB/50% RH 350C DB/240C WB +/-10C
 Occupancy-Estimated in accordance with Building Codes of Australian AS 137.186 as 10
people per 10 square metre of floor space (Davis and Gertler2015). The total tenable
floor area for level 2 office space is 700 square metres.
Occupancy= 700 sq m
10 sq m =70 People
 Lighting- 20 watts/ square metre (Ren and Chen 2015).
 Office equipment-10 watts per square metre
 Glazing-Sigle glazed from Viridiaglass V-Lam which is laminated and installed with
aluminium mullions (Shen and Li 2016).
 Outdoor air quantity-According to AS 1668.2
 Toilet exhaust air- According to AS 1668.2 and Building Code of Australia.

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1. Heat load Calculations.
The heat load determination has been done with the aid of the Carrier method using various
tables. The cooling load is given from the equation below (Olubunmi, Xia, and Skitmore 2016).
a. U-Values for the various building materials used are tabulated below. These are the
common building materials in most of Australian Office buildings. The key materaisls
include concrete for walls and slabs, gypsum ceilings, and glass for windows.

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Office HVAC Design 5
b. The peak solar gains are experienced between 11am and 4 pm in the evening. This is as
shown in the table below.

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c. The equivalent temperature difference for the walls result from the set indoor temperature
of 25 0C. The average outdoor temperature for this area is taken to be 350C. The
temperature difference is thus equal to 35-25=10 for both roof and walls.
d. The peak zone loads are estimated at the time that the office space is at full capacity. This
has been considered in this design and the peak loads have been entered in the Career
sheet.
e. For the office space, the façade displays a wide area for natural ventilation and hence the
air flows freely from the inside to outside. However, the ceiling cassesttes indoor units
allowas for make up air connetion. This is sized from the standard requirements of 15-20
l/s per person.
f. The additional information is derived from the Australian Building Standards Codes. For
instance, each peron is expected to produce 175 watts heat energy when working in an
office.
The total heat load calculated using the Carrier method, putting into account solar heat gain
factors through glass and walls, people and equipment, as well as sensible and latent heat is
496032 Watts (496.032kW). Allowing for a factor of safety and sizing the air conditioning
equipment at a capacity of 500kW would help in balancing the load. The indoor units are ceiling
concealed cassettes each of 70kW cooling capacity.
2. Psychrometric and Equipment Selection.
The Psychrometric chart for the design conditions factoring in indoor and outdoor air
requirement is as shown below. This is for Summer conditions only as per the assignment
requirement.

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3. Ductwork Design
The ductwork sized are dependent on the air flow rate as well as velocity of airflow in the
duct. For office space, the maximum allowed ducted air velocity is 4m/s as per AS 1668.2
and Constant velocity method of design has been employed.
The ductwork scope covers toilet extract system. The ductwork for toilet exhaust has
been done separately for gents’, ladies’, and disabled washrooms. The extract fans are
located on the roof level. In the washrooms, disc valves have been designed for each to
extract at a rate of 25 litres/ second as per the BCA code (Manjarres, Mera, Perea, Lejarazu,
and Gil-Lopez 2017). The final connection to the grilles has been done in a 100mm diameter
flexible duct. The main ductwork has been done in galvanized Iron duct gauge 6 according to
BCA standards.
10 air changes per hour (Ach) has been used as a standard for the public toilets as per the
AS 1668.2 code.

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Washroom Male Washroom Disabled Washroom Female Washroom
Extract rate (Ach) 10 10 10
Room Volume 20 cubic metres 10 cubic metres 15 Cubic metres
Air flow rate 200 Cu.m/hr. 100 Cu.m/hr. 150Cu.m/hr
No. of Disc Valves 5 2 4
Individual Disc valve extract 40 Cu.m/hr. 50 Cu.m/hr. 37.5
Duct Velocity 4m/s 4m/s 4m/s
Toilet exhaust and cumulative loads
Male washroom =40 Cu.m/hr. 80 Cu.m/hr. 120 Cu.m/hr. 160Cu.m/hr. 200Cu.m/hr-
Riser Duct
Disabled washroom= 50 Cu.m/hr. 100 Cu.m/hr-Riser Duct
Female washroom =37.5 Cu.m/hr. 75 Cu.m/hr. 112.5 Cu.m/hr. 150Cu.m/hr-Riser Duct
From the ductulator below, the largest duct, which is the riser duct are 230mm diameter.
This is equivalent to 200mmx200mm square duct. The rest of the branch duct is 100x100mm
with a maximum velocity of 3m/s, which is acceptable for washrooms extract.

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Reference List
Davis, L.W. and Gertler, P.J., 2015. Contribution of air conditioning adoption to future energy
use under global warming. Proceedings of the National Academy of Sciences, 112(19), pp.5962-
5967.
Harvey, T. and Sillato, S., Vertiv Corporation, 2019. Cooling System for High-Density Heat
Loads. Energy and Buildings, 112, pp.10-13.
Manjarres, D., Mera, A., Perea, E., Lejarazu, A. and Gil-Lopez, S., 2017. An energy-efficient
predictive control for HVAC systems applied to tertiary buildings based on regression
techniques. Energy and Buildings, 152, pp.409-417.
Olubunmi, O.A., Xia, P.B. and Skitmore, M., 2016. Green building incentives: A
review. Renewable and Sustainable Energy Reviews, 59, pp.1611-1621.
Ren, Z. and Chen, D., 2015. Estimation of air infiltration for Australian housing energy
analysis. Journal of Building Physics, 39(1), pp.69-96.
Shen, C. and Li, X., 2016. Solar heat gains reduction of double-glazing window with cooling
pipes embedded in Venetian blinds by utilizing natural cooling. Energy and Buildings, 112,
pp.173-183.