- Category: PROJECTS
- Published on 06 March 2017
- Hits: 184
By Ilana Koegelenberg
Charlotte Maxeke Johannesburg Academic Hospital (formerly Johannesburg General Hospital) is refurbishing ageing infrastructure and is opting for a more modern vertical hot water system to run on the steam it generates on site.
The existing hospital buildings, including its hot water system, were about 30 years old and in desperate need of an upgrade. This included the nurses’ quarters, which received a complete makeover and looks almost brand new now.
As such, the Department of Infrastructure and Development hired Masinge Vlaming joint venture as the main contractor to take on this project. They in turn appointed Allsteam Engineering to take care of the hot water generation portion of the upgrade. Brencon Plumbing got involved in the remainder of the wet services contract.
The Allsteam team has been involved in quite a few aspects of this ongoing refurbishment, and recently completed work in the nurses’ quarters where they stripped out the existing steam system completely and started from scratch. They have done three blocks such as these already, focussing on finding the most efficient solution with the resources available.
This particular installation took about six weeks to complete.
The nurses’ quarters consist of 16 floors with about 20 units on each floor. All of these units are fed from the vertical hot water system in the basement.
The existing hot water system was completely stripped out and replaced with a 2 500ℓ hot water calorifier with a 300kW heating capacity. Because of its great heating capacity, this single tank is sufficiently sized to serve the entire building. This steam-operated vessel is capable of heating 3 000ℓ/hour. (The previous system included a central heating element, but this has since been disconnected.)
Cold water is pumped from the municipal mains to a 100 000ℓ tank on the roof (seventeenth floor) from where it is fed down into the calorifier in the basement. From here, the hot water is fed up to a ring main on the sixteenth floor and fed down in branches to connect on the first floor ring main.
The hot water system heats the water to 80°C, a temperature that can be reached after only an hour and a half if the system had been off completely.
Inside the plant room, pipes have been colour-coded to mark each feed: green for cold, yellow for steam, double yellow for condensate, red for hot, and double red for the hot water return.
The water is heated by the coil of steam at five bar pressure (about 158°C) so the steam cools, creating condensate. This condensate is still high in heat energy and as the water used for the steam has been chemically treated for corrosion control, it makes the contents of this liquid valuable. This condensate is pumped back to the boiler house about 1km away, to be reused in the steam generation system.
The biggest challenge on this project was the high pressure needed to get the water up to the sixteenth floor. Almost six bar pressure is needed to achieve this, which meant that the entire system had to be built to cope with this — from the pipes to the fittings to the valves.
Another challenge was the fact that the steam can never be turned off or it shuts off the entire hospital — it has to run 24/7.
The operation requires a large amount of energy to run and as such, the hospital has its own central boiler room system that creates steam from natural gas and feeds it to the various buildings as needed. It transfers the heat from the gas to the steam. The municipality would simply not be able to provide all the energy required and if it could, it would very expensive.
The steam is used for various applications around the hospital, from the industrial kitchen, laundry, hot water systems to sterilisation in the autoclaves.
This steam is supplied at 10-bar pressure from the boiler house and reduced at each plant room to the required pressure.
As steam pressure and temperature are directly related, this is an easy way to control the temperature required for each application.
“Steam is a lot more efficient than using electrical elements in installations such as these,” explained Franco Habib of Allsteam Engineering who did the installation. “However, it’s only really feasible for quite large installations as there is a high start-up cost.”
Maintenance and lifespan
According to Habib, this system should last the hospital about 25 years if it is properly maintained. Allsteam Engineering will also be taking care of the maintenance contract to make sure this happens.
The coils will have to be changed out about every three years to keep the system running optimally. The system also requires the regular maintenance of the steam valves, pressure reducing valves, steam traps, and thermostatic controllers to ensure that leaks are repaired promptly so no corrosive fluids attack the system from the exterior.