Gravitational natural phenomena are not always able to provide sufficient circulation of the heating medium, especially in complex systems with several rings. A water pump for space heating can help stimulate the movement of the heating medium. What is this equipment? We will consider this question in our article.
Besides the device and technical characteristics of the water pump, let's consider the types, peculiarities of marking. We will also consider in detail the advantages of circulating equipment and important parameters to consider when choosing.
The contents of the article:
- General structure of a water pump
- The types of pumps for heating systems
- Option #1 - \"dry\" type devices
- Option #2 - wet rotor pumps
- Benefits of circulation devices
- Specialities of marking equipment
- What to look for when choosing a pump?
- Equipment specifications
- Equipment power
- Advanced device functions
- Other nuances of pump selection
- Conclusions and useful video on the topic
General structure of the water pump
The water pump is built into the heating circuit to allow the flow of heat medium.
It consists of the following basic elements:
- Housing with an operating chamber;
- air discharge screw;
- terminal box.
The terminal box can be equipped with additional mechanical and electronic instruments for controlling the motor operation.
The simplicity of the device ensures high reliability of the pumps, due to which they can function effectively for about 5-10 years.
When a water circulating pump is first started, the air screw must be unscrewed and the air released from the working area
Sorts of pumps for heating systems
The modern circulating pumps are divided into two basic types: \"dry\" and \"wet\". They are somewhat different in their internal structure and operating scheme, but the fluid motion in them is still provided by the circulation processes in the system. Some models are equipped with devices for automatic regulation of their operation.
Variant #1 - devices of \"dry\" type
The design of a dry circulation pump does not imply contact of the coolant with the rotor. Its working area is separated from the motor parts by rings.
They are made of the following types of material:
- tungsten carbide;
- stainless steel;
- aluminium oxide.
The dry pump working principle consists in the rotation of a wheel in a medium of heat carrier. The water inlet is in the center of the main chamber and the outflow system on the periphery.
The operating area of the \"dry\" circulators is only connected to the motor via a shaft and can therefore be replaced if required
The rotation of the impeller of the function wheel generates centrifugal forces that move the heat transfer medium from the center of the casing to the edges. This principle of operation of circulation pump enables continuous water movement through its inner chamber.
The positive features of dry type heating equipment are as follows:
Due to the combination of economy and noisiness, dry pumps are used preferably in heating systems for industrial, office buildings and large housing blocks.
Hence the following disadvantages for this kind of units:
- High noise level making it impossible to use them in apartments.
- Need to replace the sealing discs every 2-3 years.
- High risk of leakage to the outside if the working chamber is leaking.
- Needs external cooling of the motor.
High weight makes these units to be installed on the floor or suspended from brackets.
The elements of the cantilever pump are fixed on a single base and the electric motor with the impeller in the casing are connected via gearbox
There are two variants of construction of \"dry\" pumps:
- Monobilized151>. The motor and the metal housing of the unit are integrated into a single construction with specific mountings.
- Consolidated. All motor capacities can be attached to the housing using universal brackets.
\"Dry\" circulators for heating systems are more durable with proper maintenance and are therefore gradually replacing wet rotor models from the market.
Variant #2 - Wet rotor pumps
The operating principle of the wet rotor circulator is similar to its \"dry\" counterpart: the rotation of the impeller moves the medium fed in the center to the periphery of the working chamber from where it is collected in the discharge channels.
All internal seals in the \"wet\" pump are static and not subject to dynamic wear, therefore these models are more reliable and durable
The rotor of the \"wet\" pump is in contact with the heat transfer medium, which also provides cooling of the motor. These units should not run dry because they quickly overheat and burn out.
The component parts of the equipment are usually located in the same housing and form a single structure, so when individual elements break down, they are not replaced but a new pump is purchased.
The heat carrier inside the working chamber has a rather convoluted path, therefore the smoothness of the inner casing material determines the pump noise
The advantages of the \"wet\" type rotor unit:
- noiseless operation;
- compact size;
- insignificant power consumption (30-50 W);
- long maintenance-free operation;
- relatively low cost;
- easy installation.
The devices are often built directly into the design of household boilers, facilitating the choice of equipment for the consumer when installing the heating system.
Heaters of this type also have drawbacks:
- The structural limitations of maximum power;
- lower maintainability;
- low efficiency (40-60%);
- must be installed on the motor axis.
Because of their low capacity, the \"wet\" type of pumping units are used mainly in heating systems of apartments and single-floor houses.
The advantages of circulation units
Before 1990, heating systems in private housing were mainly designed and built without pumps. The heating medium moved through the pipes by gravity, and its circulation was ensured by convection flows of the fluid when it was heated in the boiler. Nowadays the systems with natural circulation are still used, though not so often.
Inexpensive solid fuel boilers are produced without built-in pumps, because the manufacturer does not know the parameters of the heating circuit. For such systems the purchase of a water pump is obligatory
The coolant movement is forced by water pumps, which have several advantages:
- Lower load on the boiler by reducing the temperature difference in the incoming and outgoing pipe.
- Even distribution of heat to the rooms due to the uniform temperature of the heating medium along the entire length of the heating rings.
- Ability to regulate the heating medium temperature in an instant.
- Fast heating of the heating system when a cold boiler is started.
- No need for pipes with a slope towards the boiler allowing uncontrolled movement of the heating medium.
- Availability of thin pipes taking up little space in the apartment.
- The pump power allows the heating circuit to be pressurized in order to transport the heating medium up several floors.
- Use of shut-off valves in the individual heating loops.
- Can be integrated into the automatic boiler control.
With many advantages, circulation units have two disadvantages - dependence on electricity and additional electricity costs.
But these are easily compensated - installation of a water pump allows to save 10-20% of fuel and the share of electricity costs in the total heating costs is only 3-5%. Besides, in case of frequent power shortage a UPS can be installed which would provide autonomous boiler and pump operation for a certain period of time.
Properties of equipment marking
Unified requirements to marking of circulating pumps, unfortunately, do not exist. Manufacturers choose their own list of specifications, which are indicated on the body of the device.
You should not be guided only by the marking when buying a pump. It is better to open the instruction manual and read the technical specifications there
The front panel usually shows this information:
- direction of the heating medium;
- diameter of pipes to be connected;
- the maximum allowable pressure;
- manufacturer and model;
- maximum operating temperature;
- defense rating;
- operation parameters of the power supply;
- the marks of conformity to national technical regulations.
Manufacturers may indicate other information at their discretion. Detailed technical specifications of the instruments are given in the instruction manual.
Dimensions differ from country to country, therefore the numerical markings on the case may be deceptive. It is better to open the instruction manual once more and note the units of measurement in addition to the characteristics.
What to look for when choosing a pump?
The selection of a single pump for the heating circuit must be done with many parameters in mind.
Technical parameters of the equipment
Circulation equipment has several characteristics that are especially important to consider when buying.
- CPD-the ratio of the amount of energy expended to the useful work done in pumping the heating medium.
- Pressure-the pressure difference between the pump outlet and inlet ports.
- Water supply-the maximum volume of heating medium pumped through the working chamber at the minimum resistance of the heating circuit.
- Pipe diameter is the nominal value of the equipment to be connected.
- Maximum nominal pressure (denoted PN) in the operating circuit at 20°C, which still guarantees the long operation of the appliance within the warranty period.
These data is usually sufficient to prove the suitability of the pump for the heating system.
The selection criteria are explained in more detail in this article.
Sufficient power of the device
The selection of the particular model of circulation equipment is determined by the technical characteristics as well as by the financial possibilities of the buyer and the properties of the heating system. If you want to save money, it is important that the pump capacity is sufficient for normal operation of the boiler. After all, the level of water supply indicated in the instructions is always much higher than the actual.
To determine the sufficiency of the capacity of the appliance yourself, three stages of calculations must be performed.
Step #1 - determine the pump capacity
Finding the required pump capacity using the formula.
The required heating power depends strongly on the material of the walls, the existence of gaps in the floor and the tightness of the window frames
For apartments in multistoried buildings the heating power is taken as 75-80 W/m², for houses - 100-120 W/sq.m. The temperature difference at the boiler's input and output is usually 10°C.
It turns out that for an apartment of 60 sq. m. the real pump capacity of (80*60)/(1,16*10)=414 (l/h.) will be sufficient.
Step #2 - calculate the head value
Calculate the head value to overcome the total system resistance according to the formula.
Each shut-off valve has its own head value which is determined with special tables. The calculation takes into account the resistance values of all pipe elements
The above formula requires complex calculations using reference data, therefore a simplified graph can be used for domestic and apartment heating systems.
The pressure loss in an apartment with 20 mm pipe diameter is strongly dependent on the pipe diameter and therefore the larger of the two possible sizes must be chosen
In accordance with the graphics, the pressure loss in an apartment with 20 mm pipe diameter is 70 mm/m and with 50 m pipe length - 3,5 meters. This figure should be multiplied by the factor 1.3-2.2, taking into account the resistance of the water fittings.
Step #3 - Determine pump capacity
Determine if the pump capacity is sufficient according to the pressure and flow graph.
Inadequate water pump capacity results in excessive gas consumption in the boiler and can even lead to fatal breakdowns
This graph is indicated in the operating instructions and is unique to each pump model. If the point of intersection of the parameters calculated above is below curve B, the appliance is suitable for the heating system, if higher, it is not.
Detailed recommendations for circulator calculation with concrete examples we have given in the following article.
Additional appliance functions
If constant fluid movement is critical for a heating system, a pair of pumps in series in the circuit can be installed. The second motor in such a system can be switched on if the capacity is insufficient or if the first motor fails.
Pumps with a thermostat and timer can be used to automate the operation of the boiler with heating from the heating circuit. An integrated mechanism allows the motor to switch on and off depending on the temperature of the heating medium and the time of day.
The terminal box can have adjustment knobs and a display panel. LCD displays on heating pumps are rarely used due to intolerance to high temperatures
Circulation pumps with a thermostat and continuously variable speed impeller can be used in branched heating networks. With their help the speed of the heating medium is regulated autonomously in different loops, depending on its temperature. Pumps with automatics cost many times more expensive and are rarely used in apartments and small residential buildings.
In the market there are both models with standard and non-standard construction, which gives additional functionality. The rating of the best heating pumps, based on the reviews of real users, we have given here.
Other nuances of pump selection
It is important that the equipment not only performs its function, but also works long without causing inconvenience to the occupants of the house or apartment.
This is why the following rules should be followed when choosing an appliance:
- Pick well-known pump manufacturers: Calpeda, Grundfos, WILO. The price of their equipment is 20-40% higher, but the probability of breakdown is much lower.
- Buy a device with characteristics that are 20-30% higher than designed. This reserve will reduce the operating load and increase the life of the equipment.
- Please pay attention to the dimensions so that the pump will fit in the space allotted to it.
- The operation of the device should be as quiet as possible so as not to disturb the inhabitants at night.
- Do not try to buy a model with power that strongly exceeds the calculated parameters. This will only lead to overconsumption of electricity but also to unnecessary noise. Pump should be chosen specifically for heating systems because they are designed for working temperatures up to 130-150 °C.
- It is advisable that the device has a built-in mesh to filter solid particles suspended in the heat medium.
The performance characteristics of the equipment must necessarily match the heating system parameters, this is impossible to save on. In addition you will have to pay only for a reliable manufacturer, increased protection of the housing and a system of automatic regulation of operation.
Most of the household circulators for heating do not require setting. To start them, it is enough to connect the nipples to the pipeline and plug the device into the power grid. And how to properly perform the installation of the pump we have considered in the step-by-step instructions.
Conclusions and useful video on the topic
How to choose a good circulation pump for heating:
Circulation equipment DAB:
Comparing two Grundfos devices: UPS and Alpha2 models:
The selection circulation pump should be agreed with the specialists. If the capacity of the equipment for a standard apartment can also prompt the salesman in the store, then before buying a heating device for a country house you will have to turn for complicated calculations to professionals.
We should remember that you cannot exchange it in the store after the start of operation, so it is better to buy a suitable model immediately.
Would you like to complement our article with useful recommendations on choosing a pump for heating? Or have you noticed a discrepancy in the data presented? Write your remarks in the comments box - we will take your opinion into consideration.
And maybe you still have questions after reading the article? Ask our experts, ask for advice - we'll do our best to help you.