City Hall Cardiff - Wales |
Five
approx. 5 feet diameter propellor fans manufactured by
Blackman & Co provide the supply air that warms
the building. The supply air for the building is all
fresh air.
These fans then discharge the supply air through large walkway sized brickwork ducts which are located under the Ground Floor corridors. From these walkway ducts smaller riser ducts are connected to supply air to the individual rooms at both floor levels of the building. Each riser duct is contained within the fabric of the building structure. All branch duct connections within the basement walkway ducts have a steam heater battery installed to warm the supply air, and is fitted with a flap type volume control damper (VCD). Each VCD has a lockable control position. Each room in the building has a supply air grating fitted in the wall at high level. A bottom hinged flap damper is fitted to each supply grating which controls the amount of warmed air that can enter the room. The flap damper has a pull cord which allows the room occupant to vary the amount of air entering the room which then provides a course control of the room temperature. The extracted air from each room is through a similar sized air register fitted at low level which provides the return air path into an extract duct which is contained within the fabric of the building. This extracted air is then discharged into large brickwork walkway ducts located above the ceiling of the ground floor corridors. In the walkway duct are two extract fans each of double inlet centrifugal pattern, The fan casing is of an unusual design having a 3/4 scroll size sitting on a concrete base. The impellors are fitted with paddle blades. The fan shaft speeds are in the range of 60 to 100 rpm. The fans due to their large size and restricted location appear to have been delivered to the site in managable sections and then erected in situ, assembling the various sections by simply bolting them together. The fans then discharge the vitiated air into the main brickwork extract tower which houses the chimney and four internal riser ducts that discharge at high level, one to each elevation of the chimney. |
Belt drive with propeller fan blades |
Note the curvature of the brickwork surround |
Supply fan belt drive showing propeller fan blades |
|
Typical layout of walkway plenum duct |
Typical layout of walkway plenum duct |
Pairs of finned steam heater batteries |
Steam & Condense pipework to heater battery |
Three quarter size centrifugal extract fan |
Three quarter size centrifugal extract fan |
Internal view of paddle blades |
Internal view of paddle blades |
Looking into discharge outlet one extract fan |
Main extract tower housing chimney and extract ducts |
High level supply air inlet with flap dampers and pull cords |
Low level extract grating |
|
The original arrangement for controlling the high level flap dampers was effected through a wall mounted key operated winding mechanism, which would vary the amount of warm air entering the room. This mechanical arrangement was dispensed with as the turn keys were so often misplaced. |
The
Assembly Room and Marble Hall have an independant
heating & ventilation system with their own supply
and extract fans. The supply air before entering the
heater batteries is first passed through a filter screen
which uses coke lumps assembled into separate open caged
cells. The coke removes the particles of dust and smoke
from the fresh air supply. The coke screen was washed
and cleaned by cold water from a high level storage tank
which fed a sparge pipe (now removed). This arrangement
of filtering the supply air using coke to remove odours
was a precursor to what nowadays is known as activated
carbon filtration. A steam heater battery warms the air before it is supplied to the Assembly Hall through ceiling outlets, and the Marble Hall through high level outlets. Extracted air is removed through low level registers. |
Six banks of filter cells filled with coke |
Coke brickettes used to filter and clean the supply air |
Original cold water storage tank supplying washer |
Extended belt drive to the supply fan |
The
heating system that serves the building is from a
design patented by The American Steam Heating Company
which developed a steam heating system which operates
at sub-atmosphere pressure with vacuum pumps that drew
the steam around the pipework, and then returned the
condensate back to a hotwell for reuse in the steam
boilers. Ashwell & Nesbit reached an agreement
with the American company and installed the system
named the "Nuconomiser" under licence in the UK. This
installation is given the number 18, so it would be
interesting to know where the previous 17
installations were located. D M Nesbit was later
granted a Patent for a modification to this type of
atmospheric system that became known as the
"Nuvacuumette".
Two GWB Powermaster steam boilers were installed in 1968 replacing the original two solid fuel boilers. They operate at a working pressure which varies between 40 and 55psi according to the varying loads imposed by the building. Safety valves are set at 62psi. The main pressure reducing valve with a downstream pressure set at 1.2 - 1.5psi. supplies the sub atmospheric steam distribution pipe system. The steam pipework feeds the fresh air heater batteries. The vacuum pump operates at 16-17psi to provide the necessary pressure differential to induce the steam around the pipework, and return the condensate to the hotwell. Steam
fed natural convectors are installed to provide
heating to the transient areas, Corridors, Foyer and
Entrance Hall.
Both boilers and vacuum pumps have a duty/standby facility operating a weekly changeover. An electric vacuum pump is also installed to provide emergency back-up. |
Left side Vacuum Pump |
Right side Vacuum Pump |
|
|
Condense trapping set from single heater |
Nameplates showing connected equipment |
A very interesting discovery was made of a sectional radiator manufactured by Ashwell & Nesbit which they called the "Ventilating Solar Radiator". This is the only example of an Ashwell & Nesbit radiator that has been found. |