The heat transfer medium (water) arrives at the manifold and from there is distributed in a suitable way to the individual terminal units (heat emitters). Manifolds are mostly made of brass, but you may also come across aluminium alloy or copper.
Applications
Installations with manifolds are used primarily for heating residential buildings, but also in the heating systems of schools, hospitals, offices, hotels, sports halls and the like.
Figure 1.5 shows an example of an independent installation with manifolds. An installation of this kind makes it possible to keep the temperature of the heat transfer medium supplying all the heat emitters at an almost constant value.
One of the most important principles when designing with manifolds is choosing the correct position in relation to the heat emitters: the manifold must be located so that the connections to the individual terminal units are as short as possible, so that the hydraulic balance of the circuit is not unduly disturbed, and so that the layout of the individual components compensates for any imbalance. For this reason installations with manifolds are often called "spider installations"; the layout is shown in Figure 1.6.
In some cases "twin-pipe" valves are used: this avoids having to chase holes into walls in order to fit thermostatic radiator valves to the top of the radiators and isolating valves to the bottom, particularly where the radiator sits in a wall recess under a window. The size of the radiator can also be changed so that, by oversizing it, the efficiency of condensing boilers is increased. A typical example is shown in the diagram in Figure 1.7.
An installation with manifolds is, because of the principle on which it is based (horizontal distribution), extremely well suited to dividing the heating system into zones. The building's heating system is split into several smaller units (usually a day zone and a night zone) or into separate sub-units (e.g. in multi-family houses) which are supplied from the same heat source, with consumption in each zone monitored by meters.
Advantages of installations with manifolds
Systems with manifolds are more favourable in energy terms: they do not require larger diameters for the pipe · running from the manifold to the heat emitters, and both the energy losses and the available head required from the pumps are lower. This in turn means lower electricity consumption and, depending on the heat output of the boiler, a smaller number of heat emitters needed to heat the space.
The advantages of this solution can be summarised as follows:
1. Uniform temperature and the same time for the system to reach full operation.
In installations with manifolds the hot medium flows into all the heat emitters at the same time. They reach full operation very quickly, and at roughly the same moment for all emitters, which shortens the transitional phase in which thermal comfort is less than ideal.
2. Ease of installation
Copper or plastic pipes are ideal for these systems: they simplify installation because they are easily bent materials that allow rapid commissioning, which means lower costs. In addition, the connections to the manifold and to the heat emitters are made with mechanically secured couplings, so no specialist work (e.g. welding) is needed. Connecting the heat emitters in parallel (a characteristic feature of installations with manifolds) makes it simple and effective to fit thermostatic radiator valves to every terminal unit.
3. Costs
Compared with other installations, a solution using manifolds involves longer distribution pipe runs for all the branches and for connecting the heat emitters. On the other hand, smaller pipe diameters are used. This usually results in lower installation costs.
4. Available head in the system
Manifolds cause only a limited pressure loss, so the useful head available at the circulation pump is higher.
5. High efficiency of the heat emitters.
The temperature at the inlet to the heat emitters is almost constant. This means better thermal efficiency of the emitters and also that there is no need to oversize them (which is otherwise a very common feature of both one-pipe and two-pipe systems).
6. The option of dividing the heated spaces into zones
These installations are extremely well suited to being divided into several thermally independent zones, so that the required temperature can be maintained in each zone and its heat consumption metered.
There are a few negative aspects that count against this type of heating installation; they are more or less minor, but they also need to be taken into account.
• A more complex method of sizing the distribution circuit compared with, for example, one-pipe installations. This is not a particularly troublesome aspect, and it brings one advantage: thanks to their layout, installations with manifolds allow check calculations to be carried out and do not require verification sizing of the system.
• The need to create an independent circuit for every heat emitter. This aspect certainly limits the range of applications of this solution, because in refurbishments, for instance, the floors would have to be replaced.
• Higher costs for building work. Using pipes made of soft materials (copper or plastic) means they have to be protected against crushing and impact by suitable covering.
Practical advice
• Manifolds are mostly housed in a dedicated cabinet, which in most cases is recessed into the wall. The manifold cabinet should be easy to reach for inspection, so we place it in a readily accessible location. It sometimes happens that the user puts furniture or fittings in front of the manifold cabinet. This makes it harder to inspect, maintain and adjust the manifold.
• Wherever possible, the rule is not to place any concealed joints in the wall or floor. Positioning the manifold roughly centrally in relation to the heat emitters avoids this situation.
• It is always advisable to insulate the pipe properly. Attempting to make use of the heat in the pipe carrying the heat transfer medium to the heating system, as though it were a small heating panel, often leads to reduced living comfort and even to physiological discomfort.
• Once the pipe has been laid - and before the cement screed is applied - it is advisable to provide protection for the pipe, for example with a small amount of mortar. The mortar protects the pipe against accidental damage.
• After the whole installation has been commissioned, it is good practice - after a certain period of operation - to check the tightness of the couplings.