Thursday, February 24, 2011


In this post, I bring you a mechanical services design I carried out for one of my projects.  The building is a 1-storey lecture block was designed to seat 640 students in eight classrooms in addition to office spaces and laboratories.
The building is a 1-storey block which seats on an approximate area of 2,190 m2. Each floor comprises 4 lecture rooms of total area 960 m2 and administrative offices occupying a total of 960 m2. The administrative area also has an 80 m2 library on each floor.
The building has an apex height of 10.5m from the lowest point. An average ceiling-floor height of 3m exists on all floors.
The toilet areas on each floor were in three sections as shown with a total of 26 WCs and 26 Wash basins. The architectural drawing used for this design is shown below.

To download large size of the above image click on the link  
The floor plan of the building is above. Note that some of the floor plan details have been removed in the drawing shown as this is for educational purpose for the topic being treated here.
The scope of the mechanical designs covered (here in this post); Design of the water supply system.

In the course of the design of this project I sought guidance from relevant technical materials (See references for further reading).  The tables shown below were also used in the course of this design.
Type of Building
Storage in Litres
Dwelling houses & flats per residents
Hostels per residents
Hotels per residents
Offices without canteens per head
Offices with canteens per head
Restaurants per head/per meal
Day schools per head
Boarding schools per head
Nurses’ homes & medical quarter per residents

Table A. Provision of Cold Water to cover 24-hour interruption of supply C.P 310 Water Supply.1

Type of Appliances
Rate of Flow (litres/s)
W.C flushing cistern
Wash basin
Wash basin with spray taps
Bath (private)
Bath (public)
Shower (with nozzle)
Sink with 13mm taps
Sink with 19mm taps
Sink with 25mm taps

Table B. Recommended minimum rate of flow rate and appliances. 2

  • British Standard Institute BS 3402 (Quality of Vitreous China Sanitary Appliances)
  • BS 3505 (Unplasticized Polyvinyl Chloride  Pressure Pipes for Cold Portable Water)
  • BS 4514 (Unplasticized PVC Soil and Ventilating Pipes)
  • The National Plumbing Code
  • Uniform Plumbing Code
  • Code of Practice 304, 1968
In the course of the design of the project I sought guidance from relevant technical materials, some mentioned here.
The services design was carried out in the following stages.
1.      Planning and layout of water distribution and drainage pipe work
2.      Design calculations and analysis
3.      Final design drawings

There was no supply from the public mains. For this project a 200mm diameter borehole was sunk to provide water which is passed through a treatment plant and the water is stored in an over head tank located on a 6.5 m high structural steel stanchion.
No provision was made for ducting of the toilets. The piping was embedded in the walls to shield them from public view. The soil type being laterite soil has good absorbing potentials for water.


The layout of the water distribution network followed a consideration of design recommendations and standards of practice some of which are mentioned here.

Storage Tank Capacity
The building was considered a mixed use building from the statistics given in the section, Description of Project. The population size used in this design was from the brief given by the client; each classroom was to seat 80 students,  each library to seat 50 people, staff list on each floor was given as 40.
 The Table A. was used as a guide to estimate the storage requirement of cold water for the building type being considered in this project.
From Table A, The per head storage requirement is for a school is 27 litres while for an office without canteen is 37 litres. Considering the above, the later was used in designing storage capacity for the project.
Going by number of staff, Storage capacity = 80 x 37 = 2,960 litres.
Going by number of students, Storage capacity = 80pple  x  4 classrooms  x  2 floors x 27 = 17,280 liters.
A storage tank capacity of 70,000 liters (14,000 gal) was used for the project to cover 4 day uninterrupted flow.
The design procedure used for pipe sizing was as follows

  1. The pipe work layout was drawn on the building plan
  2. The appropriate demand units, DU, for each sanitary fixture was indicated on the layout.
  3. The sum of all the demand units were calculated along the pipe work to the source which in this case is the overhead storage tank.
  4. The demand units were converted into flow rates and recorded accordingly using a pipe sizing chart.
  5. The head of water H, in meters, was determined for each floor.
  6. The Equivalent length, EL, of the pipe run to each floor was determined. This was approximated as the measured length plus 30 % to account for the frictional resistance of bends, tees and other fittings in the pipe work.
  7. Determine available pressure loss rate, H/EL.
  8. Determine the index circuit. This is the pipe circuit with the lowest H to EL ratio.
  9. With the DU known, this was converted to flow rate using the pipe sizing chart.
  10. Armed with H/EL (converted to kPa), the chart was used to select pipe sizes.
Follow the link below to download the isometric of the piping layout for the building.
Isometric Drawing 1 (complete)
Pipe Sections A and B
Pipe sections C and D

The pipe sizing data is represented in the drawing by the notation
Where DU       =  Demand  units
Q           =   Rate of flow in  l/s
H/EL    =   Ratio of available head to equivalent length of the pipe run to each floor in meters
 D     =   Selected pipe diameter, in millimeters
Taps and ball valves are served with 18mm diameter pipes as recommended for sanitary fittings.
Calculations for pipe sections A and B are  shown here as a sample calculations to show how the above parameters (Q, H/EL, DU and D) used in the drawing were gotten.

The measured length of pipe from the storage tank to the furthest fitting on the 1st floor, the basin is,

L1 = 4+0.6+2.4+0.6+1.350+35.89+5.05+35.16+9.63+0.9+1.950+3 + 1.75 = 102.28 m

And the equivalent length of the circuit to the basin is,

EL1 = 1.3 x 102.28 m

       = 132.96 m
The head loss rate is,

H1        =    4 m           =  0.03 m head/m run.
EL1               132.96
Similarly, for the ground floor circuit to the basin the measured length is:

L2 = 4 +0.6+2.4+0.6+1.350+35.89+5.05+35.16+9.63+0.9+1.950 + 1.75= 99.28 m

And the equivalent length EL2 ,

            = 1.3 x 99.28 m          = 129.06 m

The head loss rate is,

H2        =    7 m           =  0.054 m head/m run.
EL2               126.79

The pipe run to the 1st floor has the lowest H/EL ratio; this is the index circuit. H1/EL1 is the available pressure loss rate, which drives water through the upper part of the system. Branches to other fittings on the same floor level can be sized from the same figure.

The measured length of pipe from the storage tank to the furthest fitting on the 1st floor, the basin is,

L3 = 4+0.6+2.4+0.6+1.350+35.89+5.05+35.16+0.9+1.950+3 + 3.37+.75 = 96.77 m

And the equivalent length of the circuit to the basin is,

EL3 = 1.3 x 96.77 m

       = 125.8 m

The head loss rate is,

H3        =    4 m           =  0.032 m head/m run.
EL3               125.8

Similarly, for the ground floor circuit to the basin the measured length is:

L4 = 4 +0.6+2.4+0.6+1.350+35.89+5.05+35.16+0.9+1.950 +3.37+.75 =  90.07 m

And the equivalent length EL4 ,

            = 1.3 x 97.53 m

            = 117.09 m

The head loss rate is,

H4        =    7 m           =  0.06 m head/m run.
EL4               117.09

1.    Table A. “Provision of Cold Water to Cover 24-hour Interruption of Supply”
Building Services and Equipment. Volume 1, P.4,  F. Hall M.I.O.B, M.I.P.H.E., Published by Longman Group Limited London
2.    Table B. “Minimum Number of Plumbing fixtures”
Environmental Engineering And Sanitation. 3rd edition. 1982. P.1000, Joseph A. Salvato, P.E., Publisher: John Wiley & Sons, New York.
3.   CHADDERTON, DAVID, V.; BUILDING SERVICES ENGINEERING, 5TH ED.,  Published by Taylor & Francis, London, 2000

4.   BARRY, R.; THE CONSTRUCTION OF BUILDINGS VOL. 5 BUILDING SERVICES. Published by Blackwell Science, UK, 1998

5.   MERRITT, FREDERICK S.; BUILDING AND ENGINEERING SYSTEMS DESIGN. Published by Van Nostrand Reinhold Company, NY,1979

1 comment:

  1. The building is a 1-storey lecture block was designed to seat 640 students in eight classrooms in addition to office spaces and laboratories. Office Interiors