City Hall
Cardiff - Wales

Cardiff City Hall is an imposing building enhansing
the Civic Centre
area of the Welsh Capital City

Building programme 1900 to 1904 - Architects:  Lanchester, Stewart and Rickards.
Main Contractor - Mesrs E Turner & Sons Cardiff.

The Building
Engineering Services Contractor for the project was Ashwell & Nesbit
of Leicester who manufactured and installed the majority of the H&V equipment.

At the opening ceremony in 0ctober 1906 the official programme lists the
heating engineers as
James Playfair and David M Nesbit, who were both
Directors of Ashwell & Nesbit Ltd.

The building is rectangular in shape and predominantly two storey with some
inner annex areas, larger Assembly, Committee Rooms and Council Chamber.

The main corridor is sited around all four inner elevations of the building.
Beneath these corridors are located the Plenum warmed air walkway ducts
that provide the airways for the warmed air which heats the 200 rooms
of the building.


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
flap dampers
was effected through
a wall mounted key
operated winding
mechanism, which
would vary the
amount of warm
air entering the

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.

Isometric layout of the plant and pipework in the Boiler House

Left side Vacuum Pump

Right side Vacuum Pump

Main pressure / vacuum  indicator panel

Details of the Heating Contractor and Installation

This nameplate was probably removed from one of the
solid fuel boilers that were replaced in 1968

Condense trapping set from single heater

Nameplates showing connected equipment

A very interesting

discovery was made of

a  sectional radiator

manufactured by

& Nesbit which they called

the "Ventilating Solar


This is the only

example of an Ashwell &

Nesbit radiator that has

been found.

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