In a vicious circle

DHW pump UP20–15 (GRUNDFOS)
UPS heat­ing pump32–120F (GRUNDFOS) flanged
RL pump30/70 (WILO)
To select a pump, first deter­mine the para­me­ters of the oper­at­ing point of the sys­tem, which is plot­ted on the Q, H graph. The pump char­ac­ter­is­tic curve must not be low­er than the oper­at­ing point of the sys­tem
The speed switch is locat­ed on the pump ter­mi­nal box
Three-speed pump UPS25–60 (GRUNDFOS) with a wet rotor and a cast iron body for heat­ing sys­tems, the max­i­mum head of which is 6m, and the feed- 3.3m3/h Atof this pump, the inlet and out­let pipes are arranged in a line, which makes it easy to mount it. The dis­tance between the noz­zles, called the base of the pump, is 180mm
Spe­cial taps for pump instal­la­tion (BUGATTI)

Pumps for the heat­ing sys­tem:
a-VA65/130 (DAB) with a max­i­mum head of 6.3m and feed 3m3/h;
b- three-speed pump for Star RS heat­ing sys­tem25/6–3P (WILO) has a head of 6m and feed 3.5m3/h

The result of installing a pump with a cast iron cas­ing in a DHW sys­tem. After a year of oper­a­tion, the pump failed due to jam­ming of the rotor of the elec­tric motor. The ini­tial sav­ings turned into high costs for the pur­chase and instal­la­tion of a new device. DHW pump hous­ings are made of cor­ro­sion-resis­tant mate­ri­als such as stain­less steel or bronze

Not so long ago, sys­tems with forced cir­cu­la­tion of the coolant were an inac­ces­si­ble lux­u­ry for own­ers of pri­vate hous­es. Such equip­ment was used exclu­sive­ly in munic­i­pal and indus­tri­al net­works. Now, with increased require­ments for com­fort and ener­gy sav­ing, cir­cu­la­tion pumps are wide­ly used in every­day life.

Why do you need a circulation pump

Accord­ing to the laws of physics, the oper­a­tion of a water heat­ing sys­tem is based on the cir­cu­la­tion of a coolant. In order for the heaters to give off the required amount of heat, the coolant flow must be suf­fi­cient (this is deter­mined by cal­cu­la­tion). The cir­cu­la­tion of the coolant can be nat­ur­al and forced. Nat­ur­al is achieved due to the dif­fer­ence in the den­si­ties of the heat­ed and cooled liq­uid, forced- using a spe­cial cir­cu­la­tion pump.

Nat­ur­al cir­cu­la­tion sys­tems require sig­nif­i­cant fuel con­sump­tion due to the need to main­tain a high tem­per­a­ture of the water in the sup­ply line. After all, the high­er the tem­per­a­ture of the water, the low­er its den­si­ty and, con­se­quent­ly, the high­er the speed of move­ment through the pipes. When oper­at­ing such a heat­ing sys­tem, it is dif­fi­cult to main­tain a com­fort­able tem­per­a­ture in the premis­es, since it is prob­lem­at­ic to use ther­mo­sta­t­ic shut-off and con­trol valves in sys­tems with nat­ur­al cir­cu­la­tion. Need­less to say, today’s pop­u­lar under­floor heat­ing with­out a cir­cu­la­tion pump can­not be equipped?

The cir­cu­la­tion pump in the hot water sup­ply sys­tem (DHW) is need­ed first of all in order to be able to get hot water imme­di­ate­ly by open­ing the tap at any point of the water intake. Also, heat­ed tow­el rails can be con­nect­ed to the DHW sys­tem, for the oper­a­tion of which the cir­cu­la­tion of the coolant is nec­es­sary.

ATunlike water-lift­ing ones, which raise water to a cer­tain height, cir­cu­la­tion pumps only make it move in a vicious cir­cle. The pur­pose of such equip­ment- pump the required vol­ume of coolant, over­com­ing the hydraulic resis­tance of pipelines and sys­tem ele­ments.

Pump selec­tion and a lit­tle the­o­ry

The main para­me­ters of the cir­cu­la­tion pump are the head (H), mea­sured in meters of water col­umn, and the flow(Q), or pro­duc­tiv­i­ty mea­sured inm3/h Max head- this is the great­est hydraulic resis­tance of the sys­tem that the pump is able to over­come. In this case, its sup­ply is equal to zero. The max­i­mum flow is the largest amount of coolant that can be pumped in 1h pump when the hydraulic resis­tance of the sys­tem tends to zero. The depen­dence of pres­sure on the per­for­mance of the sys­tem is called the pump char­ac­ter­is­tic. Atsin­gle-speed pumps have one char­ac­ter­is­tic, two- and three-speed pumps- respec­tive­ly two and three. AtVari­able speed pumps have many char­ac­ter­is­tics.

The selec­tion of the pump is car­ried out, tak­ing into account, first of all, the required vol­ume of coolant, which will be pumped over the hydraulic resis­tance of the sys­tem. The flow rate of the coolant in the sys­tem is cal­cu­lat­ed based on the heat loss of the heat­ing cir­cuit and the required tem­per­a­ture dif­fer­ence between the direct and return lines. Heat loss­es, in turn, depend on many fac­tors (ther­mal con­duc­tiv­i­ty of build­ing enve­lope mate­ri­als, ambi­ent tem­per­a­ture, ori­en­ta­tion of the build­ing rel­a­tive to car­di­nal points andetc.) and are deter­mined by cal­cu­la­tion. Know­ing the heat loss, cal­cu­late the required flow rate of the coolant accord­ing to the for­mu­la Q=0.86Pn/(tpr.t-tarr.t), where Q- coolant con­sump­tion,m3/h; Pn — nec­es­sary to cov­er heat loss­es, the pow­er of the heat­ing cir­cuit, kW; tpr.t- tem­per­a­ture of the sup­ply (direct) pipeline; tarr.t- return line tem­per­a­ture. For heat­ing sys­tems, the tem­per­a­ture dif­fer­ence (tpr.t-tarr.t) is usu­al­ly 15–20C, for under­floor heat­ing sys­tem- 8–10FROM.

After deter­min­ing the required flow rate of the coolant, the hydraulic resis­tance of the heat­ing cir­cuit is deter­mined. The hydraulic resis­tance of the ele­ments of the sys­tem (boil­er, pipelines, shut-off and ther­mo­sta­t­ic valves) is usu­al­ly tak­en from the cor­re­spond­ing tables.

Hav­ing cal­cu­lat­ed the mass flow rate of the coolant and the hydraulic resis­tance of the sys­tem, the para­me­ters of the so-called oper­at­ing point are obtained. After that, using man­u­fac­tur­ers’ cat­a­logs, a pump is found whose oper­at­ing curve lies not low­er than the oper­at­ing point of the sys­tem. For three-speed pumps, the selec­tion is car­ried out, focus­ing on the sec­ond speed curve, so that there is a mar­gin dur­ing oper­a­tion. To obtain the max­i­mum effi­cien­cy of the device, it is nec­es­sary that the oper­at­ing point is in the mid­dle of the pump char­ac­ter­is­tic. It should be not­ed that in order to avoid the occur­rence of hydraulic noise in pipelines, the coolant flow rate should not exceed 2m/s. When using antifreeze, which has a low­er vis­cos­i­ty, as a coolant, a pump is pur­chased with a pow­er reserve of 20%.

For clar­i­ty, con­sid­er an exam­ple of choos­ing a pump for a cot­tage with an area of ​​​​200m2where a two-pipe heat­ing sys­tem made of polypropy­lene pipes with a diam­e­ter of 32mm and length 50m. Tem­per­a­ture chart of the heat­ing sys­tem- 90/70C. Assume that the heat loss of the house is 24kW. Then the required mass flow Q=0.8624/(90–70)=1.03m3/h We find the hydraulic resis­tance accord­ing to the table- it is 1.8mbar/lmm. For a pipe length of 50m resis­tance will be equal to 90mbar, or approx­i­mate­ly 0.1bar=onemwater.Art. Add to this the resis­tance of the ele­ments of the sys­tem, equal to, say, 1mwater.Art. Point options: Q=1.1m3/h, H=2m. We will select the pump accord­ing to the GRUNDFOS cat­a­log (Den­mark). For our pur­pos­es, a three-speed UPS mod­el is suit­able.25–40, herthe cost is 108.

Pump energy efficiency

Cur­rent­ly, man­u­fac­tur­ers of pump­ing equip­ment are pay­ing more and more atten­tion to the ener­gy effi­cien­cy of their prod­ucts. Accord­ing to this indi­ca­tor, all elec­tri­cal appli­ances are divid­ed into class­es, denot­ed by the let­ters of the Latin alpha­bet- from A to G. Kclass A includes the most eco­nom­i­cal devices to date. Con­ven­tion­al one or three speed pumps have class lev­el ener­gy con­sump­tionC. At the same time, the pow­er of the devices is rel­a­tive­ly low: in terms of ener­gy con­sump­tion, they are com­pa­ra­ble to incan­des­cent lamps of 75 or 100Tue Toclass A can only belong to pumps with elec­tron­ic speed con­trol of the rotor of the elec­tric motor. In addi­tion, the low noise lev­el gen­er­at­ed by their elec­tric motors can be not­ed.

Cir­cu­la­tion pumps with fre­quen­cy reg­u­la­tion at 50–70% is more expen­sive than usu­al, so their use should be jus­ti­fied. For exam­ple, it does not make sense to use an elec­tron­i­cal­ly con­trolled pump if there is no ther­mo­sta­t­ic shut-off valve in the heat­ing sys­tem, and the tem­per­a­ture of the heat­ing cir­cuit (device) changes not due to a decrease in the mass flow of the coolant, but as a result of a change in the tem­per­a­ture of the water in the sup­ply line (using three- or four-way ser­vo valve).

Pump device

Cir­cu­la­tion pumps are divid­ed into two large groups: with a wet and with a dry rotor. As the name implies, in the devices of the first group, the rotor rotates direct­ly in the coolant, which in this case plays the role of a lubri­cant. The sta­tor is iso­lat­ed from the rotor by a sleeve. The advan­tages of such a pump are sim­plic­i­ty of design, small dimen­sions and weight, low noise lev­el, and a wide range of man­u­fac­tured mod­els. Tothe dis­ad­van­tages include the pos­si­bil­i­ty of rotor jam­ming due to the accu­mu­la­tion of deposits on its sur­face, as well as a small­er range of ambi­ent tem­per­a­tures at which the device can func­tion nor­mal­ly. ATIn pri­vate homes, pumps with a wet rotor are main­ly used.

Pumps with a dry rotor are dis­tin­guished by the fact that the rotor of the elec­tric motor is con­nect­ed to the impeller shaft of the pump through a mechan­i­cal seal and does not come into con­tact with the coolant. The advan­tage of this design lies in the pos­si­bil­i­ty of using elec­tric motors of greater pow­er and, as a result,- in greater device per­for­mance. A wider range of ambi­ent tem­per­a­tures should also be not­ed, since the engine is less sus­cep­ti­ble to heat­ing from the coolant. The dis­ad­van­tages of such pumps are rather impres­sive dimen­sions and a high­er noise lev­el than devices with a wet rotor.

The stan­dard oper­at­ing tem­per­a­ture range of those and oth­er cir­cu­la­tion pumps- 2–110C. Such indi­ca­tors cor­re­spond, for exam­ple, to the UPS mod­el25–60 (GRUNDFOS, Den­mark; price- 130) or VA 25/180 (DAB, Italy; price- 82). Devices in a spe­cial design are able to oper­ate at a coolant tem­per­a­ture from ‑25 to +140C. The pos­si­bil­i­ty of oper­at­ing a pump with a coolant that has a neg­a­tive tem­per­a­ture will be use­ful to those who leave the house for a long time in the cold sea­son, turn­ing off the heat­ing (in this case, it is nec­es­sary that an antifreeze coolant be poured into the sys­tem). Run­ning such a device at a tem­per­a­ture in the house - 10–15C will pass with­out prob­lems, while a pump with a nor­mal tem­per­a­ture range may dete­ri­o­rate. Pump hous­ings for heat­ing sys­tems are made of cast iron, and for DHW sys­tems- only in stain­less steel or bronze. The impeller is usu­al­ly made of heat-resis­tant plas­tic.

Some unscrupu­lous instal­la­tion orga­ni­za­tions install cast iron pumps in DHW sys­tems, which allows the cus­tomer to save a small amount. Pay­ing for these sav­ings- an increase in the iron con­tent in the DHW sys­tem and the like­li­hood of jam­ming of the pump rotor due to accu­mu­la­tion of deposits, up to the fail­ure of the elec­tric motor.

For ease of instal­la­tion, the inlet and out­let pipes of the pump are locat­ed in one line (the so-called in-line ver­sion).

To pro­tect the engine when the rotor is jammed, some mod­els of pumps are equipped with ther­mal relays that break the pow­er cir­cuit when over­heat­ed. There are pumps that are not afraid of jam­ming,- with the so-called spher­i­cal rotor. ATIn these mod­els, the mag­net­ic field is trans­mit­ted from the sta­tor to the rotor in the aquat­ic envi­ron­ment, through the con­duc­tive parts of the pump. ATUnlike tra­di­tion­al wet rotor devices, the spher­i­cal motor does not have bear­ings. The cham­ber with the rotor is her­met­i­cal­ly sep­a­rat­ed from the sta­tor by a stain­less steel spher­i­cal cup. ATAs a result, this type of pump is less sus­cep­ti­ble to the effects of impu­ri­ties and lime deposits con­tained in the water. It is very easy to dis­man­tle the device for clean­ing with­out remov­ing the hous­ing from the pipelines. In this case, you just need to dis­con­nect the elec­tric motor from the hous­ing by turn­ing the thread­ed ring. Note that pumps with a spher­i­cal rotor are avail­able only for domes­tic hot water sys­tems.

ATIn crit­i­cal cas­es, so-called twin pumps are used to increase the reli­a­bil­i­ty of the sys­tem. ATthey have one impeller dri­ven alter­nate­ly by one or the oth­er elec­tric motor. The lat­ter are locat­ed in a com­mon build­ing. When one of them fails, the oth­er one auto­mat­i­cal­ly turns on. ATIn nor­mal mode, for uni­form oper­at­ing time, the engines replace each oth­er at reg­u­lar inter­vals. Such a pair is some­what cheap­er than two con­ven­tion­al devices. So, for exam­ple, the UPD mod­el32–80 F (GRUNDFOS) offered at a price 644.

Comparative characteristics of circulation pumps for heating systems (voltage- 230AT)

Man­u­fac­tur­er Mod­el name Head, m Feed, m3/h Pow­er con­sump­tion, W Price,
GRUNDFOS UPS 25–60 6 3.8 90 130
Alpha 25–60 6 3.8 90 170
UPE 25–60 6 3.3 100 242
WILO Star RS 25/6 6 3.5 99 122
Top‑E 25/1–7 7 6.4 200 521
DAB VA 25/180 2.5 3 55 76
VEA 55/180 5.2 3 91 82
NOCCHI PUMPS R2S 25–70 7 4.8 140 129
KSB Rio 25–7 7 7.2 185 235
VORTEX HZ 401–25 four 3.2 78 75
WESTERLINE WP 425 four 2.3 78 62

Comparative characteristics of circulation pumps for hot water systems (voltage- 230AT)

Man­u­fac­tur­er Mod­el name Head, m Feed, m3/h Pow­er con­sump­tion, W Price,
GRUNDFOS U.P.15–14B com­fort 1.4 0.73 25 113
UP 20–30 N 3 2.7 95 214
UPS 25–60B 6 3.7 90 283
WILO Wilo Star‑Z 15 C 1.24 0.46 28 177
Wilo Star‑Z 20/1 1.7 1.1 38 147
DAB VS 16/150 1.58 1.8 48 135
NOCCHI PUMPS R2X 20–30 3 2.4 87 184
VORTEX BW 401 four 3.2 78 220

Features of the use of pumps in hot water systems

Usu­al­ly, a large capac­i­ty pump is not required to cir­cu­late hot water. But the oper­at­ing con­di­tions of such a mod­el dif­fer sig­nif­i­cant­ly from the con­di­tions of heat­ing sys­tems. The high oxy­gen con­tent in tap water does not allow the use of devices with a cast iron body in this case.

Poor­ly treat­ed water (with a high con­tent of hard­ness salts) leads to the for­ma­tion of lime deposits on the pump rotor. This occurs most inten­sive­ly at a water tem­per­a­ture of more than 55–60C. To pro­tect equip­ment from such a scourge, many man­u­fac­tur­ers sup­ply their devices with ther­mostats that turn off the pump when the coolant reach­es a “dan­ger­ous” tem­per­a­ture. For ease of oper­a­tion and reduc­tion of ener­gy costs, it is advis­able to turn on and off the cir­cu­la­tion pump of the DHW sys­tem accord­ing to a cer­tain pro­gram.

If the pump is con­nect­ed to a mod­ern boil­er con­trol pan­el, this prob­lem is solved at the soft­ware lev­el. If the boil­er is equipped with a stan­dard con­trol pan­el or a pan­el that does not sup­port the con­nec­tion of a DHW cir­cu­la­tion pump, you can pur­chase a pump with a built-in timer, for exam­ple, mod­el BWZ152 (VORTEX, Ger­many) worth 120.

For the oper­a­tion of the boil­er for the heat­ing sys­tem and heat­ing the water in the boil­er, GRUNDFOS pro­duces a com­bined pump UPP15–50. It con­sists of two pumps in a com­mon hous­ing. One of them is designed to cir­cu­late the coolant in the heat­ing sys­tem, and the oth­er is the load­ing pump of the indi­rect heat­ing boil­er. ATdesign includes a divert­er valve. Mod­el cost- 228.

Manufacturers and prices

Pumps from such com­pa­nies as GRUNDFOS (Den­mark), VORTEX, KSB, WILO (Ger­many), DAB, WESTER LINE (Great Britain) andetc. The cost of cir­cu­la­tion pumps for heat­ing sys­tems is rel­a­tive­ly low: 70–80 per device with one shaft speed, pro­duc­tiv­i­ty 2–3m3/h and pres­sure 4–5m. Pumps with fre­quen­cy reg­u­la­tion of the same pow­er will cost the con­sumer 120–150. The price of more pow­er­ful devices used in heat­ing sys­tems for cot­tages with an area of ​​700–800m2can reach 500–700 and more. But the life of the pump- at least ten years with con­tin­u­ous oper­a­tion, so such costs can be con­sid­ered insignif­i­cant. Prices for cir­cu­la­tion pumps for DHW sys­tems start from 80–90.

Pump installation

The pump is installed on the sup­ply pipeline, in a pipe sec­tion. To con­nect, use quick-release con­nec­tions with a union nut (“Amer­i­can”) or spe­cial taps for strap­ping. Shut-off valves for the instal­la­tion of pump­ing equip­ment are offered by OVENTROP (Ger­many), GIACOMINI, BUGATTI (Italy) and oth­er man­u­fac­tur­ers. The cost of one crane with a diam­e­ter of 1inch- 7–10. Dur­ing instal­la­tion, it is impor­tant that the axis of rota­tion of the motor is in a hor­i­zon­tal plane. If the heat­ing sys­tem has a mem­brane expan­sion tank, the pump is locat­ed after the point of its con­nec­tion in the direc­tion of move­ment of the coolant. This arrange­ment of equip­ment allows for more effi­cient removal of air.

At the end of the instal­la­tion of the entire sys­tem, it is filled. We must not for­get that after start­ing the pump with a wet rotor, it is nec­es­sary to remove air from its cham­ber. To do this, set the max­i­mum engine speed and unscrew the pro­tec­tive cap. Water begins to come out of the hole with air bub­bles. When it comes out, the cap is twist­ed again. By the way, the pres­ence of air in the pump can cause noise.

Rotor jam prevention

Some­times pumps remain idle for a long time. to pre­vent jam­ming of the shaft, they must be peri­od­i­cal­ly turned on for a short time. If you have a mod­ern con­trol pan­el, such as Loga-mat­ic 4211 (BUDERUS, Ger­many; cost- 1300), there is no need for pre­ven­tive mea­sures, since every­thing will be done by automa­tion. But if the jam­ming of the rotor could not be avoid­ed, do not despair. Unscrew the pro­tec­tive cap on the end of the shaft, insert a flat screw­driv­er into the slot on the shaft and turn the rotor sev­er­al times.

We would like to thank RUSKLIMAT, STK-GROUP and the rep­re­sen­ta­tive office of GRUNDFOS for their help in prepar­ing the mate­r­i­al.

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