Background
Dividing a heating installation into zones is the ideal design solution for a building in which different parts have different thermal comfort requirements or are used at different times. The individual zones may be dwelling units or, as already mentioned in this publication in connection with independent systems, parts of them: a day zone, a night zone, or a zone occupied only at irregular intervals.
The installation in each zone is fitted with a room thermostat on which the desired temperature can be set (see Figure 1.8).
Advantages of zoned installations
Dividing a heating installation into several zones (most commonly a day zone and a night zone) has a beneficial effect on thermal comfort and saves energy.
Implementing zoned installations
Multi-zone installations can be implemented in several ways, the most common being the following:
1. using a zone valve (with or without end microswitches)
2. using (electric) circulation pumps
In the first case, each thermostat acts through a zone valve whose job is to open and close the hot water supply to the heat emitters in the zone concerned, according to the demand of that room or space. Heat is therefore produced in exactly the quantity needed to achieve the desired thermal comfort. See also Figure 1.9.
In the second case, the thermostats control electric pumps, as shown in Figure 1.10. A notable feature of this diagram is the use of a device called a low loss header, which is not needed in the first case (zone valve instead of a pump).
The low loss header is a very important component in hydraulic circuits and may be encountered under various names: "hydraulic separator"; "hydraulic mixer" and so on.
It is an open manifold in which the boiler flow communicates with the return from the heating system and which hydraulically separates the primary (boiler) circuit (boiler - low loss header) from the secondary (load) circuit (low loss header - heating system). In this way, circulation in the primary boiler circuit is provided by the boiler pump (i.e. the circulation pump fitted in the boiler at the factory), while the secondary load circuit is given the necessary temperature difference (and hence the correct water flow rate) specified by the heating engineer.
A hydraulic separator must be installed whenever the boiler alone cannot provide the flow rate required in the system:
in that case the water coming from the boiler mixes (in a correctly sized low loss header) with part of the water returning from the load circuit, so that circulation in the secondary circuit is noticeably higher than in the primary circuit.
Function of the low loss header
• To reduce or cancel out the negative effect of the available head generated by external circulation pumps, which undesirably affects the operation of the pump pressure switch in the boiler
• to prevent any unwanted flow that might occur in the zones served by the boiler's circulation pump. At the same time (unlike zoned installations with zone valves), the low loss header offers the option of increasing circulation in the individual zones.
As illustrated in the diagrams in Figs. 1.9 and 1.10, zoned installations can be implemented in two ways as far as water temperature is concerned:
a) with the same water temperature;
b) with different water temperatures, known as mixed systems.
In both cases the installation options are very varied.
