Meet the ancestor

A few months ago I came across some old back issues of the IHVE Journal. They made interesting if rather unnerving reading, for what we like to kid ourselves as being advanced engineering was standard practice years ago.

History, it is said, is often what we care to remember. Mortality also has a habit of eroding wisdom, leaving us with only musty technical papers, conference proceedings and journals, such as this, as a record of the industry's collective experience. We innovate, we forget, and then inevitably we reinvent.

The Shell Centre is the exception that proves the rule. Nearly fifty years after it was conceived many of its innovative services survive in full working order. Virtually the entire record of its construction – drawings, progress photographs, site minutes, and correspondence – still exist, carefully filed away in the company's archives. And what one finds there is evidence of a building which, if it were designed today, could easily justify many column inches in the construction press.

At an IHVE meeting in February 1963 Haden's design engineers recorded with great prescience that the Shell Centre was a building of "solidity and permanency...designed to give a high standard of living for the occupants...for many years". The sheer magnitude of the project told the engineers that very few existing ideas and practices could be taken for granted. Innovate, was the order of the day.

Design standards
Many of the design standards would put many recent buildings to shame. For a start, the roof was insulated to a U-value of 0.2 W/m2K.

The windows were chosen on the basis of their high thermal performance. Not only were the windows double-glazed to increase noise resistance, they were designed with a mid-pane venetian blind – a sign of quality even today.

The windows are wood-framed and horizontally pivoted, which enabled them to be cleaned from the inside – a virtue not shared by contemporary mirrored curtain walling. They were not openable by the occupants of course, but then you can't have everything.

Just when our Building Regulations are getting all excited over fabric airtightness, it is sobering to report that the Haden's engineers knew all about the virtues of low infiltration. "When closed such windows should be reasonably airtight", they said, noting, without irony, that: "the length of the gap around the frames which requires sealing is considerable". It was not thought necessary to use an inflatable rubber gasket, worsted cord being used for the job.

At 27-36%, glazed area is slightly under what today would be considered ideal for daylighting. It isn't coated to prevent heat loss as the technology wasn't then available.

Most of the other design standards have slightly higher design margins than would be acceptable today. The structural floor loads, for the air-handling plant room for example, were 250 lb/ft2. This equates to 11.9 kN/m2 compared to today's standard of 7.5 kN/m2 as defined in the BCO Specification.

Ventilation and air conditioning
It was decided at the outset that the Shell Centre should be sealed and fully air conditioned – a UK first.

"Because the site was both dirty and noisy, and from the knowledge of the extraordinarily rapid increase in office air conditioning in America...air conditioning would give the standard of comfort likely to be required by the Shell staff", recorded Haden's technical director (and IHVE past-president) H C Jamieson.

It was a bold decision. At the time no one had contemplated an air conditioned building of this size in Europe, let alone the UK. Jamieson and his executive engineer J R Calland had started a ball rolling, and they knew it.

Product selection took over two years, from 1955 to 1957, largely because the choice of air conditioning equipment was not exactly large. The choice was also limited by currency restrictions, dollars not being available to purchase American products.

The ventilation rates are remarkably similar to today's norms. Fresh air was supplied at low velocity at about 16.5 l/s/person at an average overal density of 10 m2/person. Generous by today's standards, but of course most people would have been smokers.

Curiously, Haden's designers felt it necessary to quote a ventilation rate of 7.4 l/s (15.75 cfm) for occupancy densities of 1 person per 4 m2 (45 ft2/person), an unthinkable density by today's standards, and probably for areas like typing pools.

Choice of cooling system
The designers considered five different types of air-conditioning system – including radiant ceilings, induction systems, double-duct systems and fan convection. After considering the virtues of these systems and taking the advice of a Mr C S Leopold of Philadelphia, the engineers settled on the Frenger radiant ceiling – almost certainly the first use of the system in the UK, as the IHVE Journal recorded:

"The main advantage of radiant cooling lies in the fact that less space is required for pipes to transfer heat by water than for ducts to transfer heat by air. The Delta T of pumping water is a small fraction of the cost of delivering air for the same heat transfer. The air supply may be substantially reduced to that required for ventilation and humidity control and approximately half the cooling load".

With reasoning like that around in the 1950s, it's a mystery as to why vav systems ended up dominating the UK air conditioning market. In any event it took until the mid-1990s before radiant systems – now called static cooling and heating systems – became common currency.

The success of the Frenger radiant ceiling system at the Shell Centre is evident by the fact that the original system is still working, 40 years on. The acoustic ceiling tiles may have been replaced, but the pipework has not. Despite steadily increasing equipment loads over the years, the radiant system has performed well.

Measurements of the air movement were made by instruments, smoke tests and the impressions of a few men and one woman

The designers were concerned that the high water pressure (about six feet at full load) might contribute to acoustic disturbance in the office space. Full-scale tests were carried out by the Building Research Station on a mock-up.

Under very quiet conditions some hissing was audible when the automatic control valves were close to their seats. Some "objectionable" noise also occurred when the head across the valves was increased to 30 ft, "a value which might occur with the low water flow in the system and the pumps near shut-off pressure".

This led to the introduction of a pressure controller on the water circuit operating a throttling valve on the pump return to restrict the head across the modular control valves. "The system's control characteristics will also be considerably improved by this addition" said Haden's engineers.

Comfort conditions
"The ultimate result of all our efforts as heating and air conditioning engineers is the comfort of the occupant, whose view of the matter can only be defined in broad terms. Indeed, comfort in physiological tests is often defined as a condition which some to 15% of the occupants will find uncomfortable".

Bear in mind that this quote from the IHVE Journal1 pre-dates all the comfort work carried out by Professor Fanger.

The internal temperature in winter was taken as 200C (680F), with a "small percentage" of the offices at up to 22. 70C (730F) through operation of modular temperature control. In summer, the internal temperature was set at 22-240C (73-750F) with a dewpoint of 12.50C (54.50F).

Humidity control set points were nothing if not specific. In winter, the designers were working between 37-44% rh, and in summer between 49-54% rh.

The design engineers were also well aware of the importance of good air movement, to the extent that a full-scale mock-up of a typical office was built early in the project for testing the air distribution from the proposed inlet grilles. This mock-up also helped to check the relationship of the architectural and engineering components.

Measurements of the air movement were made by instruments, smoke tests and the impressions of "a few men and one woman". Unfortunately, the facilities at the engineers' disposal were limited. They could not control the air inlet temperature over a wide enough range, and measurements of air movement were not considered to be numerous enough:

"As this basic design is repeated several thousand times in this building, more expensive and detailed tests would have been desirable and reassuring...however, such results as we did obtain gave us enough confidence to proceed".

Haden's engineers noted that zonal temperature control was becoming "inadequate" for heating installations:

"Many American office buildings had thermostatic room control eight years ago... and today it appears to be a standard provision in the higher class buildings".

Modular thermostatic temperature control was provided at Shell for every 9 ft (sic) of the office areas. The system was pneumatic. A thermostat operated two control valves, one on the outer ceiling grid which supplied heating in winter and cooling in summer, and a second on the inner ceiling grid which supplied cooling all year round. Fifty miles of quarter inch diameter nylon tube was used in the connections.

Despite their enthusiasm for innovation, Haden's engineers were nothing if not "sound". These were the days of high temperature hot water systems, and the system at the Shell Centre ran at 1500C. To protect the pump bearings from overheating they were cooled by mains water.

Control of expansion was also a very important issue. The boiler plant was provided with a vertical cylindrical expansion vessel with a capacity of 1500 gallons (6817 litres), large enough to take the whole of the expansion likely to occur even after a prolonged shut down. To take care of the unlikely event of steam formation in the boiler the engineers used a closed tank with of watertight construction with a large vent and overflow. The outlets were positioned so that a discharge of steam or water through them would pose no danger.

This solution came under question, as the IHVE Journal dryly reported:

"During the course of the contract, some stir in a musty corner of an insurance company caused them to ask that steam escape pipes or open vents be fitted to the boilers on the ground that this was an open system.

The request was politely refused...on the grounds that they could be dangerous even in normal conditions with a boiler temperature of 3000F".

Novel materials
As one might expect from a company that has substantial interests in the chemical field, the building featured extensive use of plastics throughout.

About 22 miles of plastics pipe were installed and this was claimed at the time to be the largest installation of plastics pipe anywhere in the world. PVC was also used in many forms, including floor tiles, railing covers, wall coverings and cable sheathing – allegedly about 400 miles of it. PVC in thin rigid sheets was also used for exhaust ducting in a battery-charging room, where the atmosphere was corrosive.

Expanded polystyrene was used in thin boards for thermally insulating air conditioning ductwork and roof top plant rooms. It was also used to lag chilled water pipes. Engineers today would recoil at the use of translucent polystyrene sheet for luminaires, but then, of course, it was the in thing.

River cooling
Not content with designing the UK's first air conditioned building, Haden's engineers roped in the River Thames as part of the cooling circuit (figure 1). The compressors were designed to run when the external wet bulb temperature rose above 100C (500F). The chilled water circuit was designed to run at 13.30C (560F).

The engineers noted that for long periods during the winter the River Thames was well below that temperature. It was obvious that a heat exchanger between the river water and the chilled water circuit could enable the river to do the cooling for a good period during the winter. A heat exchanger large enough to handle the load was installed, along with a 27 inch main large enough to borrow 4 million gallons a day (18 million litres) from the Thames. Finally, how about this for the first UK air conditioned building. The engineers recognised that, in winter, they would be considerable heat gain to the cooling circuit. When the plant was running in humidification mode, the chilled water supply was re-routed so that the chilled water return went through the air coolers first before going back to the central plant. The designers calculated that the return water from the circuits could be up to about 630F.