Originally each flat provided it's own hot water from a coke stove in the
kitchen, and heating was by open coal fires throughout the flat.
At some time a communal heating and hot water system was installed, with service pipes being introduced through each flat. This was originally fuelled by coal and subsequently converted to oil and then to gas.
There are three boiler houses on the Estate, each with two boilers and two calorifiers, and three calorifier rooms each with two further calorifiers.
Heating is by the direct system, that is the water is heated though the boiler and pumped directly around the radiators to the flats and common areas.
The hot water is produced by an indirect system, with the hot water from the boilers being pumped through coils in the calorifiers where the heat is transferred to heat up the fresh cold water in the calorifiers and which is then pumped to the taps in the flats.
We may get a request from a leaseholder to move one of the communal heating or hot water pipes in their flat when they are considering carrying out alterations. Such requests are referred to Keywater Services who will advise what can be done, and the likely cost to the leaseholder. Sometimes we are advised by Keywater that the requested modification should be refused as it would involve additional 90° bends. Below is Keywater’s reasoning behind advising such a refusal.
The Heating & Hot Water Service systems at BAM Estates are approximately 80 years old, and still basically sound, however, they were never installed to modern standards. A large percentage of the circulation achieved in these systems is by convection rather than pump. In this way the systems can operate with relatively small pumps for the size of the system. A modern system would ignore convection flow and ensure that the pumps were sufficiently large to circulate the system adequately. To adapt the systems would require much larger pumps, altering systems to pressurised systems, and installation of a regulating valve on every riser.
Convection is the name given to the effect of heat rising and cold falling. This effect operates in these systems anywhere there is a long length of vertical pipe. The heated water wants to rise creating an upward pressure which lifts the heated water to the roof. Cooling water wants to drop creating a dropping pressure causing the water to drop. The effect is similar to a circulating pump in that any long vertical pipe in the system creates a pressure which results in a flow. A long vertical pipe in this installation, therefore, is called a convection pump.
The heated flow pipe work rises to the roof, this rise is our first convection pump, the hot water is then distributed to various drops (also known as risers!) through the building, these are the large pipes which run through the flats, and each of these pipes is a small convection pump assisting the flow as the hot water cools. Without this convection flow there would be insufficient flow in the system to keep your radiators hot, and hot water at the tap outlets. Having each of these risers as a convection pump reduces the need for balancing the system, as the convection flow draws the hot water to the furthest points on system. However, this means that a restriction in any one riser will adversely affect the flats on that riser as the hot water is not drawn to that area of the building.
The problems associated with reduced flow rate are accentuated by the release of air. Hot water contains a fairly high level of dissolved gases. All the time the temperature and the rate of flow are maintained these gases remain in solution or as small air bubbles throughout the system to the outlet. A relatively small reduction in the flow rate of the system will allow this air to escape to form larger air bubbles at the top of system. These we call air locks. This trapped air bubble restricts the flow of water still further allowing more air to escape. Finally the trapped air will stop the flow completely.
With this in mind we are concerned not to allow any alterations to the systems which will restrict this convection flow. A 90° elbow is just such a restriction, it takes energy to overcome the turbulence created and force the water through 90°. This energy is taken from the flow energy created by convection and the pumps. It has, therefore, been decided that additional 90° bends should not be allowed in the risers on the systems. We will allow 45° bends since they cause a much lower obstruction to the flow.