Comparison Grundfos UPA 15-90 8 m

3/4"

vs Wilo Star-RS 25/6 6 m

1 1/2"

180 mm

The main application for which the pump is designed.

— Central heating. By the name, pumps are designed to circulate the heating medium in the heating system. It avoids stagnation and ensures the efficiency and uniformity of heat transfer; without a pump, the circulation intensity would be insufficient due to the high hydro-resistance of the system. A mandatory feature of units for this purpose is the ability to operate at a high temperature of the pumped liquid (see below) — about 95 °C, or even more. Note that this allows the use of such pumps also in cold and hot water supply systems (see below); however, this can hardly be called the best option — models for heating usually cost more than other types due to high heat resistance and performance, and these are redundant in the DHW circuits.

— DHW recirculation. Pumps whose task is to move water along the domestic hot water circuit. Such units are used in autonomous hot water systems — in other words, houses and apartments with their own water heaters. Constant circulation ensures uniform distribution of water throughout the circuit; in fact, this means that after opening the corresponding tap, you do not have to wait until hot water reaches the point of disassembly from the heater — it will immediately be hot. Like the central heating pumps (see above), DHW pumps can work with high-temperature water; however, for most models, the max...imum temperature (see below) is 60 – 65 °C; therefore, such a unit cannot be installed in the heating system. At the same time, some exceptions can withstand up to 95 °C — they differ quite conditionally from heating pumps, mainly due to lower performance (usually less than 600 – 700 L/h). With cold water, models for this purpose usually cope without problems.

— TCold water pressure boost. Pumps are designed to provide additional pressure in the cold water circuit — for example, if the pressure in the water supply drops or if the main pump supplying the system with water does not reach the required pressure. The key difference of this type from the others described above is the low operating temperature (maximum — less than 60 °C) and, accordingly, the impossibility of working with hot water.

Many models allow use in other areas than those described above — for example, models for DHW recirculation may be suitable for operation in air conditioning or refrigeration systems.

The maximum flow of a pump is the amount of liquid it can pump in a certain amount of time.

Features of choosing the optimal performance option depend primarily on the purpose of the pump (see above). For example, for DHW recirculation models, the pump performance should not exceed the performance of the water heater. If the water heater is capable of delivering 10 litres per minute to the DHW circuit, then the maximum pump performance will be 10*60=600 L/h. The basic formula for calculating the performance of a heating system takes into account the power of the heater and the temperature difference at the inlet and outlet, and for the cold water system — the number of points of water intake. More detailed information about the calculations for each application can be found in special sources, and it is better to entrust the calculations themselves to professionals.

The head can be described as the maximum height to which a pump can lift liquid through a vertical pipe without bending or branching. This parameter is directly related to the pressure that the pump produces: 10 m of head approximately corresponds to a pressure of 1 bar (do not confuse this parameter with operating pressure — see more about it below).

The head is one of the key specs for most circulation pumps. Traditionally, it is calculated based on the difference in height between the location of the pump and the highest point of the system; however, this principle is relevant only for units that boost the pressure of cold water(see "Suitable for"). Circulation pumps for heating and DHW work with closed circuits, and the optimal pressure depends on the total hydraulic resistance of the system. Detailed calculation formulas for the first and second cases can be found in special sources.

The lowest pressure in the circuit where the pump is connected, at which it can perform the main task (see "Suitable for"), providing the claimed operating parameters. The technical features of many modern models are such that some of them can operate at almost zero pressure, simply by the presence of water in the pipe; therefore, this parameter may not be specified at all.

The lowest fluid temperature at which the pump is capable of operating normally.

Almost all pumps can normally transfer cool water, regardless of the purpose (see above); therefore, for normal household use, this parameter is not critical and for some models, it may not be indicated at all. But if you need the ability to work with liquids with temperatures below 15 °C, you should pay close attention to the minimum temperature. Some models that can be used with antifreeze normally tolerate even temperatures below zero.

The highest liquid temperature that the pump is capable of operating normally.

The possibility of using the unit directly depends on this parameter (see "Suitable for"): for example, models for heating systems must tolerate a temperature of at least 95 °C, and for DHW supply — at least 65 °C. Well, anyway, this parameter should not be exceeded: an overheated pump will fail very quickly, and the consequences of this can be very unpleasant.

— Number of speeds. The number of speeds provided in the design of the pump. Each speed corresponds to its performance value (see above). The options could be:

• 1 speed. There are no adjustments in such models; when turned on, the pump can operate only at one speed. This is the simplest and most inexpensive option, due to the absence of additional elements (regulators) in the design. Of course, it is convenient only in cases where the unit must operate at full capacity every time it is turned on.
• 2 speeds. 2 speeds give the user some degree of choice: the pump does not have to be turned on at full power — when it is not required, the unit can be run at reduced power to save electricity and not wear out the mechanisms beyond what is necessary.
• 3 speeds. The largest number of adjustments found in modern pumps — it makes no sense to provide a larger number for many reasons. It gives even more options for setting operation parameters than 2 speeds.
• Stepless adjustment. This option implies the ability to set the regulator to any position from minimum to maximum (in some models, fixed settings may also be provided, but only as an additional option). It provides maximum freedom and precision in the choice of operating mode. However, it significantly affects the price; and the real need for smooth adjustment occurs quite rarely.

— Automatic operating mode.... The essence of this function differs depending on the purpose of the device (see above). So, in models for increasing the pressure of cold water, the automation turns on the pump when the tap is opened and turns it off when it is closed — a special sensor reacts to the movement of water. In models for heating and domestic hot water, automation is responsible for adjusting the operating parameters — for example, when screwing the valves and reducing the flow rate, the pump can reduce the pressure, as well as, for additional functions, such as an on-off timer. Anyway, this feature makes life easier for the user, eliminating the need to perform certain operations manually and adding new features to the pump; but the specific set of these features depends on the model.

— Display. Various additional information can be displayed on the display: operating mode, performance settings, water temperature, set timers, error messages and much more. It makes management more convenient and intuitive. Pumps usually use the simplest form of black and white LCD screens, but this is quite sufficient for the purposes mentioned.

— Control panel. In this case, the control panel means a panel that has a switch with a choice of operating modes between automatic (see above) and manual. Accordingly, the presence of several modes almost necessarily means the presence of a control panel. But the speed switches themselves are not considered for this function.

The electrical power consumed by the pump during normal operation and maximum performance.

This indicator directly depends on performance — after all, for pumping large volumes of water, an appropriate amount of energy is needed. And the power depends on two main parameters — electricity consumption and the load on the power grid, which determines the connection rules. For example, pumps with a power of more than 5 kW cannot be connected to ordinary household sockets; more detailed rules can be found in special sources.

It is the material from which the motor shaft in the pump is made.

— Cermet. It is a material that combines metals and their alloys with non-metallic components. In modern pumps, different types of cermets can be used, differing in price and quality; usually, the features in each case directly depend on the price category of the unit. However, it is well suited for household models with relatively low performance but is poorly suitable for professional use. Therefore, in pumps of more than 15,000 litres per hour, cermet shafts are rarely used.

— Stainless steel. This material is highly durable and reliable, due to which it is found in almost all categories of pumps — from relatively simple to professional, the performance of which is in the tens of thousands of litres per hour. However, it is somewhat more expensive than cermets.