Building Services Engineering 5th Edition Handbook

372 Plant and service areas
Air change rate from the provision of outdoor air is:
2.25 m3 1 air change
N = 3600× ×
s 30 × 25 × 6m 3
= 1.8 air changes/h
This is acceptable and reasonable. There may be additional recirculated air within the
floors from distributed terminal heating/cooling air control units such as variable air volume,
induction or fan coil units.
6. The cooling plant capacity is 30 W/m 3 = 0.405 MW, same as heating power calculated.
plant room floor area = 80.49 + 35.46 × ln 0.405 m 2
= 48.4 m 2
Data provided by Bowyer (1979) do not cover plant smaller than 0.3 MW, so this is likely to
be realistic. The floor space needed for chillers and cooling towers does not increase as fast
as for heating plant with increasing capacity.
Thus the total plant room space requirements are estimated to be
(27.6 + 1 + 52.6 + 23.8 + 48.4) m 2 = 153.4 m 2
These two methods of estimation show that plant room space requirements are of the order
of 153–405 m 2 . This is a wide spread of answers provided for the design concept stage. It will
be refined by detailed design and better knowledge of the plant loads and locations to be used.
A low-energy building has the minimum of mechanical services plant for air handling and cooling.
Heating systems have traditionally not required much plant room space and hot water radiators
and convectors are very compact, mainly consuming wall space. The historical precedent for a
9% floor area requirement is likely to be too high for a modern system.
A vertical service duct is needed from the roof plant room to ground level carrying supply and
exhaust air ducts, drainage and water pipework and cables. If the maximum air velocity in the
air ducts is 6 m/s, their sizes will be
duct cross-sectional area = Q m3 /s
V m/s
= 2.25
6 m2
= 0.375 m 2
If square ducts are used, they will be 612 mm × 612 mm or larger, such as with standard
sizes of 700 mm × 600 mm. An estimated service duct arrangement is shown in Fig. 16.4. This
allows for thermal insulation and access to all the services.
False ceilings provide space for the horizontal distribution of services. The induction units will
be located along the external perimeter under the windows or within the false ceiling. Holes
150 mm in diameter are needed in the floor slab, one for each unit, for the air duct and, close
by, two holes 50 mm in diameter for pipes.