To begin, let’s look at the heating system based on the popular wall-mounted two-contour boilers with a power up to 35 KW, in which the second contour aims to provide hot water supply. In these boilers, there are four outlets: two of them are connected to the heating system and the other two to the hot water supply. The boiler has its own circulational pump and expansion tank and it would seem that it is only necessary to install the boiler onto the wall, connect the gas supply, connect the pipes of the water supply, hot water supply, and heating system, and you can start the system. And it is really that way, but only if there is one heating contour, for example for radiators. But what should be done if, in addition, you want to have in the house not only a heating contour, but also «warm floors», especially if the power output of the boiler allows it?
The temperature of the warmth carrier in the heating system and in the system of «warm floors» is different. Therefore you can connect two different heating systems with the assistance of tees to the outlet supply from the boiler, but you have to create a scheme of balancing differential pressures in the two different heating rings. In principle, it is not that difficult, but if you do not have an engineer’s knowledge in the area of heating, you can do it more easily if you use the system of primary-secondary rings with a hydrocollector which, in this case, has the role of hydrobalancer of pressure. This technique is well known in heating systems and such a balancer is called an «arrow». The «arrow» provides a constant supply of warmth carrier through the boiler which is beneficial to its long-term work.
As an example, take the ready-made hyrdocollector «Element-Micro» from the company «Hydromontage» and connect it to the boiler and on the input outlets we put the radiator heating system and the system of «warm floors» (see Figure 54). That is the entire boiler piping.
If you need to create several contours of «warm floors», the usual collector (see Figure 55) is connected to the hydrocollector; it is important that the total supply of warmth carrier in the secondary rings does not exceed the supply in the boiler. In other words, the boiler can give the full power of its pump by rotating the hot water on the primary ring (in hydrocollector and its own contour) and consumers (secondary rings) should not pump more hot water from the hydrocollector than it can give. Otherwise, there will be water in the contours, but the boiler would not have time to heat it. The calculation of power of secondary rings is done according to the volume of the warmth carrier by selection of speed of motion of the warmth carrier in the heating contours, choosing length and internal diameter of the pipes. The sum of all the volumes of warmth carrier flowing in the secondary rings per hour should not exceed the volume of warmth carrier which is given by the boiler in the same hour.
If you use a simpler boiler, for example floor-standing, in which there is no contour of hot water supply, expansion tank, automatic air purger, or circulational pump, then these devices (see Figure 56) must be included into the heating scheme.
With increasing numbers of consumers this scheme can be changed by including the usual collectors in its chain (see Figure 57). Note that in this case, as it was in the case of the scheme in Figure 55, the number of secondary rings was not increased — it remains unchanged. One of the secondary rings was simply replaced with a two-piped collector system. Just this combination of heating systems with primary-secondary rings and usual heating systems (collector, two- or one-piped) is called a combined heating system.
How will the combined system work? Assume that in the secondary rings, four-way and three-way mixers are in the closed position, i.e. the secondary rings do not send a request for warmth carrier. In this case, the warmth carrier is being heated in the boiler and being forced by the circulational pump, it «rotates» in the primary ring — hydrocollector. The water comes to the boiler with approximately the same temperature as when it came out. This is very good for the working of the boiler; there is no thermal shock and there is no large pressure drop. All modern boilers are equipped with automatic devices which measure the temperature of the warmth carrier on the supply line. Since the water comes to the boiler hot, then it is almost unnecessary to heat it. The automatic devices order the burner of the boiler to decrease the height of the flame or to turn off completely. The boiler works in an economical mode. Further, the warmth carrier which circulates in the secondary ring gets cool and the mixer opens up — the command for demand of warmth appeared. The circulational pump of the secondary ring starts to pump the hot water from the hydrocollector through the mixer and drops the cooled water into the hydrocollector.
The return water mixing with the water in the hydrocollector comes to the boiler. The temperature sensor on the boiler detects the decrease in the temperature and immediately increases the flame of the burner. Thus the more demands there are for warmth from the secondary rings, the more the boiler will heat the water, and conversely, in the absence of requests for warmth, the boiler enters its economical mode, sometimes completely turning the burner off.
For floor boilers, with a power up to 50 KW, the hydrocollector «Compact» from the company «Hydromontage» can be used mounted on a special steel unit which is attached to the wall and the floor (see Figure 58). In this scheme, an «expanded» primary ring with soft priority of hot water heating is used. When the boiler is filled with hot water, the four-way mixer is in the off position and the warmth carrier forced by the circulational pump of the primary ring flows in both sections of the hydrocollector and comes back to the boiler. On turning the hot water on, the boiler sends the request for warmth and the mixer opens; thus the primary ring is lengthened and already includes the boiler. The automatics of the boiler are configured in such a way that allows you to customize water heating to «hard», «soft», and «parallel» regimes. In other words, while «lengthening» the primary ring, the boiler can have priority over other consumers of warmth, or work in parallel with them.
Like the previous schemes, the heating system using «Compact» hydrocollectors can be expanded to connect additional consumers (see Figure 59). For this, special inserts or usual collectors in two-piped schemes can be attached to the hydrocollector. If necessary, the standard scheme can be not extended but on the contrary, be reduced.
Let’s agree that the scheme designed for the output of the boiler up to 50KW which is able to heat a house of an area up to 500 m² will not be used by everyone. However it should be clarified that hydrocollectors designed for this power output can be used for lower warmth loads. But let me repeat again that on buying hydrocollectors, it is necessary to compare their living cross-section with the supply of warmth carrier from the boiler in such a way that the speed of motion of water in the collector is within normal range. For weak boilers, a smaller hydrocollector must be chosen; for bigger boilers, a bigger hydrocollector must be chosen. For example, for a boiler with a capacity of 30 KW, the supply of warmth carrier is 1.8 m³/hour (30 litres per min.); if we take the speed of motion of warmth carrier in the collector to be 0,3 m/sec, then the living cross-section of the collector should be:
flcs = Q/(3600×V) = 1,8/(3600×0,3) = (m³/hr)/(m/s) =1,8×(100³ cm³/hr)/3600×0,3×(100 cm/s) = 1800000/108000 = (cm³/s)/(cm/s) = 16 cm²
It can be a box of size 2×8 cm or, for example, 3×5,5 cm. If the collector of the same cross-section is taken for the boiler of power 50KW then the speed of motion of liquid in it will be 5,2 m/sec (calculations omitted) — i.e. the cross-section of this collector is not enough and must be increased. But if the power of the boiler is less, for example 15KW, then the speed of the motion of the warmth carrier in the collector will 0,26 m/sec, which is within the norms and this hydrocollector is suitable for the boiler of this power.
In heating systems with a power more than 50 KW, it is mandatory to install a balancer of pressure (other names: hydrodivider, «arrow») into the scheme (see Figure 60) of pipe setting. In this scheme, the primary ring consists of boiler contour and hydrobalancer in which the warmth carrier is circulated under the force of the boiler’s pump. The hydrobalancer (see Figure 61) provides a smooth guaranteed circulation through the boiler as well as deceleration of the flow and a decrease in differential pressure between the supply and return pipelines of the collector. When there is a demand for warmth from the consumers, the warmth carrier circulates through the boiler, hydrobalancer, hydrocollector, and the conumer’s corresponding ring. Getting warmth by the secondary rings takes place in the upper chamber of the collector.
For high-power heating systems with boilers more than 50 KW, hydrobalancers with separating nets and magnetic plates are used. The hot warmth carrier from the supply pipe of the boiler forced by the primary circulational pump flows into the hydrobalancer and, colliding with the internal wall, comes into the upper part of the body. Here there is one more internal wall which separates the air from the warmth carrier. Next, the hot water mixes with the cool water which came from the consumers and it is sent to the heating system. The warmth carrier which came from the heating system collides with the magnetic plates which attract parts of metal to it and serve as a break for the cooled water; here the water slows its course and drops the slime as sediment. Here also the mixing of the cooled water of the return with the hot water of the supply of the boiler is occurring — the heated warmth carried by the return comes to the boiler. Thus the hydrobalancer is serving simultaneously as air separator, mixer, break and slime collector.
For weak heating systems, up to 50 KW, the hydrobalancer of simpler design but not less functional is used. It is usually a rectangular tank with a live sectional area providing reduction of speed of the warmth carrier, from 0,2 to 0,4 m/sec. Due to low speed the slime drops from the warmth carrier and settles at the bottom of the hydrobalancer and the air is released and then vented by automatic air purgers. In the centre of the hydrobalancer (in the mixing chamber) 1–3 perforated internal walls are installed without hermetic welding to the perimeter. If you cut such a hydrobalancer, it is very much like a car muffler and it works in about the same way.
One of the most popular designs in hydrocollectors is the scheme of two half rings (see Figure 62); this is a variation of the scheme shown in Figure 56. The heating system on two half rings allows you to increase the number of consumers (secondary rings) but with the condition that the loads on the half rings are approximately the same. This scheme is used with boilers of any power and if one boiler is not enough, then a second boiler can be included in this scheme.
By including two or more boilers into the heating scheme, you can not only increase the heating power, but also reduce energy consumption. Instead of one boiler with a power of 55KW, you can install two boilers, for example 25 and 30 KW, or three boilers: two of 20 KW and one of 15KW. Then on a typical day in the year, the less powerful boilers in the system will work, and with a peak load all of them will be turned on.
