The document outlines the steps for designing mechanical building services, including: 1. Gathering required information such as building layout and design temperatures from guides. 2. Selecting appropriate systems based on the design brief, such as boilers, radiators, or ducted air handling units. 3. Following a design sequence including calculating heating/cooling loads, sizing ventilation, cooling, plumbing, heating, and drainage systems and components. 4. Producing drawings of the systems and ensuring all required information is included before final review.

1. How to Design Mechanical
Building Services
By David Seymour

2. Overview
The main section of the design process are as follows:
1. Information Required for design
2. Selection of system Parameters
3. Program Design Period
4. Design
5. Drawings
6. Review of Drawings

3. 1.0 Information Required
An example of the Information that
required to commence the design is:
• Building Construction (u-values)
• Building Layout / Sections
• Design Brief / outline
• Are there Planning constraints that
apply to M&E design
• External and Internal design
temperatures

4. 1.0 Information Required
What if my design brief does not cover all aspects of the design:
• This is quite common in the design of M&E services
• The gaps can be filled in by the use of CIBSE and Plumbing guides.
• External design temps can be found from the use of CIBSE guide A table
A2.4 for winter conditions and A2.6 for summer conditions
• A good table to use for internal design criteria is from CIBSE guide A table
A1.5

5. 2.0 Selection of system Parameters
To select the types of systems we have to
consider type of systems that will meet the
design brief.
• This may include for heat generation gas
boilers, heat pumps, biomass boilers and ect.
• For heating the space this may include fan
coil units, radiators, heated ducted system with
AHU’s and ect.
• For cooling the building this may include VRF
system, ducted system with AHU, Fan coils with
Chillers and ect

6. 3.0 Program of design
• This is required to plan out the stages required during the design phase

7. 4.0 Design
For mechanical design there are 5 main systems within a building.
These include, heating, cooling, ventilation, plumbing and drainage.
• These systems are often interlinked and to fully design one you
may have to have designed parts of the other.
• An example of this if the heating system is being used to heat the
incoming air to a building and the HWS.
As a result of this your design needs to be followed in a sequence.

8. To aid in this sequence it is good practice to
have all the design information to hand!!
The sequence is a follows:
1. Heat loss / heat gain figures
2. Ventilation Design
3. Cooling Design
4. Domestic water design
5. Heating Design
6. Drainage Design
Each of these sections also has its own
sequence to follow
4.0 Design

9. 4.1 Generation of Heat Loss / Heat Gain figures
The first part of this sequence is to generate the heating and cooling loads.
• To do this we will use a program like IES of hevacomp.
• Within these programs before drawing out the building you should input all the
internal / external design temps and constructions to be used. Ie the room templates
and weather templates ect.
• Once this is done the building can be modelled and the heating / cooling loads can
be obtained for each room.
4.0 Design

10. 4.2 Ventilation Design
The second part of the sequence is ventilation calculations:
1. Identify the spaces that require ventilation.
2. What type of ventilation is required (toilet extract, general extract, kitchen extract,
make up supply, general supply for occupancy or HVAC vent.
3. Obtain the flow rates for each space link up the space with similar ventilation types
to form ductwork runs and flow rates for each section
4. Size each section of ductwork (if doing this by hand note down the Pa/meter)
5. Size the fan, grilles and louvres / roof cowls
6. If the system is supplying air for fresh air only work out the amount of heat required
7. If the system is to be used to heat / cool as space you will also need to use
physchrometric charts to work out the heating / cooling loads.

11. 4.3 Cooling Design
The cooling design is dependant upon the heat gain calculations workedd out in section 4.1 and the if
relevant the cooling requirements for AHU’s in section 4.2.
Once we have this information the following sequences can be applied:
1. Size the cooling appliances
2. Link up the appliances that require Chilled water services and size the interconnecting pipework.
3. Select an appropriate sized chiller /s to suit the system.
4. Size the pump for the system
5. Size the pressurisation unit and expansion vessel
6. Add valves to the system for future isolation and flow control of the system
Note: if using a VRF system the interconnecting pipework is designed by the installer. And only the internal and external units need to be selected

12. 4.4 Domestic Water Services
The domestic water system is not dependant upon other services.
The following steps can be taken to complete the design of this section:
1. Assess the appliances that require DWS and what type, ie WC’s, WHB, sinks, showers, drinks
machines and some ovens may require water services.
2. Identify the loading units from CIBSE or demand units from the Plumbing guide for each
appliance
3. Link up the different services and use the demand units to size the pipework.
4. To size the booster set, add the HWS to CWS demand units and covert the total into L/sec and
use the height of the building to work out press required.
5. Size the CWS tank from plumbing guide table 2
6. Size the HWS cylinder from plumbing guide table 6 and work out the heating load

13. 4.5 Heating system design
The heating design is dependant upon the heat loss calculations workedd out in section 4.1 , the
relevant the heating requirements for AHU’s in section 4.2 and the heating load for the DHW
cylinder in section 4.4
Once we have this information the following sequences can be applied:
1. Size the heating appliance’s
2. Link up the appliances that require LPHW services and size the interconnecting pipework.
3. Select an appropriate sized Heat generator (gas boiler, Heat pumps, CHP, bio-mass boiler,
ect) to suit the system.
4. Size the pumps for the system.
5. Size the pressurisation unit and expansion vessel.
6. Add valves to the system for future isolation and flow control of the system
Note: if using a VRF system the interconnecting pipework is designed by the installer. And only the internal and external units need to be
selected

14. 4.6 Drainage
Drainage will be required from all WC’s, WHB, sinks, showers, AC units, AHU’s with cooling
capability
1. Assess appliances that require drainage and locate SVP’s in appropriate locations
2. Design the branches to each appliance including air vents
3. Size the main SVP’s

15. 5.0 Drawings
First decide whether you are going to do your drawing by hand or by AutoCad!!!!
1. Set out what you want on each drawing a good guide would be:
• Vent Drawings
• Heating and Cooling Drawings
• Domestic Water Drawings
• Plumbing Drawings
• Plant space Drawings
• Equipment Schedules
2. When setting out your drawings try and locate main services along corridors and branch into
rooms.
3. Each drawing should have a drawing number , titled and dated

16. 6.0 Review Drawings
Just as it says REVIEW YOUR DRAWINGS and make sure you are
happy that everything that is required is on them.

17. Conclusion
•Get all the required information first, fill in the gaps necessary
with the relevant guides.
•Select the system parameters that will meet the design brief.
•Plan out the design programme in sequence.
•Design the services following the sequences.
•Create the drawings using your service design.
•Review the drawings ensuring there is no information missing
and the design brief is met.

18. Any Questions?