Water heater for supply ventilation: selection and installation

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conventional air heater

Sup­ply air heat­ing for ven­ti­la­tion or heat­ing sys­tems pro­vides the nec­es­sary micro­cli­mate that meets san­i­tary require­ments. With­out this pro­ce­dure, the fresh jet will con­stant­ly replace the warm exhaust air, bring­ing heat ener­gy to the out­side, there­by reduc­ing the effi­cien­cy of the build­ing’s heat­ing sys­tem. One of the main devices used to pre­pare sup­ply air for sup­ply to the ven­ti­la­tion sys­tem is a heater — an air flow heater that uses the ener­gy of a car­ri­er or con­verts one type into anoth­er.

The principle of operation and design of the water heater

A heater is a device used to heat air. Accord­ing to the prin­ci­ple of oper­a­tion, it is a heat exchang­er that trans­fers ener­gy from the coolant to the sup­ply jet flow. It con­sists of a frame, inside which tubes are arranged in dense rows, con­nect­ed in one or more lines. A coolant cir­cu­lates through them — hot water or steam. The air, pass­ing through the sec­tion of the frame, receives ther­mal ener­gy from hot pipes, due to which it is trans­port­ed through the ven­ti­la­tion sys­tem already heat­ed, which does not cre­ate the pos­si­bil­i­ty of con­den­sa­tion or cool­ing the premis­es.

Types of heating devices for forced ventilation

All heaters for forced ven­ti­la­tion can be divid­ed into two main groups:air handling unit with a water heater for ventilation

  • using heat trans­fer flu­id.
  • Not using coolant.

The first group includes water and steam heaters, the sec­ond — elec­tric. The fun­da­men­tal dif­fer­ence between them is that the devices of the first group only orga­nize the trans­fer of ther­mal ener­gy enter­ing them in fin­ished form, while the devices of the sec­ond group cre­ate heat inside them­selves on their own. In addi­tion, water and steam heaters are divid­ed into lamel­lar, hav­ing greater effi­cien­cy, but worse per­for­mance, and spi­ral-rolled, which are now used almost every­where.

There are also heat­ing devices, often includ­ed in these groups, for exam­ple, a gas heater. The burn­ing gas heats the air flow pass­ing through the heat­ing zone, prepar­ing it for use in ven­ti­la­tion or air heat­ing sys­tems. The use of such devices is not wide­spread, since the use of gas in indus­tri­al work­shops is asso­ci­at­ed with a lot of dan­gers and has many restric­tions.

There are also used oil heaters. The heat gen­er­at­ed dur­ing the com­bus­tion of min­ing is used. For large rooms, such devices do not have suf­fi­cient pow­er, but for small aux­il­iary areas they are quite suit­able.

Pros and cons of using

The advan­tages include:

  • High effi­cien­cy.
  • Sim­plic­i­ty of the device, reli­a­bil­i­ty.
  • Com­pact­ness, the abil­i­ty to place in small vol­umes.
  • Unpre­ten­tious­ness in main­te­nance (water and steam appli­ances prac­ti­cal­ly do not need it).

The dis­ad­van­tages include:

  • The need for a coolant or con­nec­tion to the pow­er sup­ply net­work.
  • Lack of inde­pen­dence of work — equip­ment for sup­ply­ing air is nec­es­sary.
  • The inter­rup­tion of the sup­ply of elec­tric­i­ty or coolant means the shut­down of the sys­tem.

Both the advan­tages and dis­ad­van­tages of the devices are due to the design and do not depend on exter­nal fac­tors.

Types of heaters

There are sev­er­al types of heaters used in dif­fer­ent areas and con­di­tions.

Let’s take a clos­er look at them:

Water

volcano in the production roomThe most com­mon group of devices, char­ac­ter­ized by high effi­cien­cy, safe­ty and ease of oper­a­tion. As a heat car­ri­er, they use hot water com­ing from the cen­tral heat­ing net­work, hot water sup­ply or from their own boil­er. A water heater for sup­ply ven­ti­la­tion is the most con­ve­nient and eco­nom­i­cal solu­tion that allows you to per­form your tasks with min­i­mal main­te­nance or repair costs. The only draw­back of the device is the need to con­nect to the coolant sup­ply sys­tem, which cre­ates cer­tain dif­fi­cul­ties at the instal­la­tion stage and pre­vents a quick trans­fer to anoth­er place.



Steam

steam heater kpsk

Steam devices are com­plete ana­logues of water devices and in prac­tice dif­fer from them only in the type of coolant. The only dif­fer­ence between steam appli­ances is the large thick­ness of the walls of the tubes — 2 mm ver­sus 1.5 for water ones. This is due to the high pres­sure in the sys­tem, requir­ing rein­forced chan­nels for cir­cu­la­tion. Oth­er­wise, the devices are iden­ti­cal, have the same oper­at­ing rules and require­ments.

Electrical

electric heater

An elec­tric air heater for sup­ply ven­ti­la­tion does not need to be sup­plied with a coolant, since the heat­ing source is elec­tric cur­rent. The con­nec­tion of such devices is much sim­pler, which makes them mobile and con­ve­nient to use, but high ener­gy costs lim­it the use of this group. Most often, they are installed for local heat­ing dur­ing one-time work, used as emer­gency or tem­po­rary sources of heat.

Calculation of heater power

Heater cal­cu­la­tion pro­duced in sev­er­al stages. The fol­low­ing are defined in sequence:

  • Ther­mal pow­er.
  • Deter­mi­na­tion of the size of the frontal sec­tion, selec­tion of the fin­ished device.
  • Car­ri­er con­sump­tion cal­cu­la­tion.

Since the air­flow is known from the char­ac­ter­is­tics of the ven­ti­la­tion sys­tem, it does not need to be cal­cu­lat­ed. The for­mu­la for deter­min­ing the ther­mal pow­er of the device:

Qt u003d L • Pin • Cin • (tin — tout)

where Qt — ther­mal pow­er of the heater.

L — air flow (val­ue of the sup­ply flow).

Pv — air den­si­ty, tab­u­lar val­ue, is in SNiP.

Cv — spe­cif­ic heat capac­i­ty of air, avail­able in the tables of SNiP.

(tin — tout) — the dif­fer­ence between indoor and out­door tem­per­a­tures.

The inter­nal tem­per­a­ture is the san­i­tary norm for a giv­en room, the exter­nal tem­per­a­ture is deter­mined by the aver­age val­ue of the cold­est five-day peri­od of the year for a giv­en region.

We deter­mine the frontal sec­tion:

F = (L•P)/V,

where F — front sec­tion.

L — air flow.

P is the air den­si­ty.

V — mass flow rate, about 3–5 kg/m2•s is assumed.

Then we find the flow rate of the coolant:

G u003d (3.6 • Qt) / Cin • (tin — tout),

where G — coolant con­sump­tion.

3.6 — cor­rec­tion fac­tor to obtain the desired units of mea­sure­ment.

Qt — ther­mal pow­er of the device.

Cv is the spe­cif­ic heat capac­i­ty of the medi­um.

(tin — tout) — tem­per­a­ture dif­fer­ence of the coolant at the inlet and out­let of the device.

Know­ing the car­ri­er flow rate, it is pos­si­ble to deter­mine the diam­e­ter of the pip­ing pipes and select the nec­es­sary equip­ment.

Calculation example

heater calculation table

We deter­mine the heat out­put at a tem­per­a­ture dif­fer­ence from ‑25° to +23°, with a fan capac­i­ty of 17000 m³/h:

Qt u003d L • Pin • Cin • (tin — tout) = 17000 • 1.3 • 1009 • (23-(-25)) = 297319 W = 297.3 kW

Front sec­tion:

F = (L•P)/V = (17000 • 1.3) / 4 = 5525 = 0.55 m².

We deter­mine the flow rate of the coolant:

G u003d (3.6 • Qt) / Cin • (tin — tout) u003d (3.6 * 297.3) / 1009 * (95–50) u003d 1.58 kg / s.

Accord­ing to the data obtained from the table of heaters, we select the most suit­able mod­el.

Calculation of the heating surface

Heating Surface Area Calculation Table

The heat­ing sur­face area deter­mines the effi­cien­cy of the device. The larg­er it is, the high­er the heat trans­fer coef­fi­cient, the stronger the device heats the air flow. Deter­mined by the for­mu­la:

Fk = Q / k • (tav.t — tav.v)

where Q — ther­mal pow­er.

k — coef­fi­cient.

tav.t — the aver­age tem­per­a­ture of the coolant (between the val­ues ​​at the inlet and out­let of the device).

tav.v — aver­age air tem­per­a­ture (out­side and inside).

The obtained data are com­pared with the pass­port char­ac­ter­is­tics of the select­ed device. Ide­al­ly, the dis­crep­an­cy between the real and cal­cu­lat­ed val­ues ​​should be 10–20% greater than the real ones.

Features of the calculation of steam heaters

calculation diagram for steam air heating appliances

The method for cal­cu­lat­ing steam heaters is almost iden­ti­cal to that con­sid­ered. The only dif­fer­ence is the for­mu­la for cal­cu­lat­ing the coolant:

G=Q/r

where r — spe­cif­ic heat aris­ing from the con­den­sa­tion of steam.

Self-cal­cu­la­tion of air heaters is quite com­pli­cat­ed and is fraught with the appear­ance of many errors. If you need to cal­cu­late the device, the best solu­tion would be to con­tact spe­cial­ists or use an online cal­cu­la­tor, of which there are many on the Inter­net. The solu­tion is quite sim­ple, you just need to sub­sti­tute your own data in the win­dows of the pro­gram and get the desired val­ues, on the basis of which you can select ready-made devices.

Strapping methods

strapping scheme

The heater pip­ing is a com­plex of devices and ele­ments for reg­u­lat­ing the sup­ply of coolant to the device. It includes the fol­low­ing ele­ments:

  • Pump.
  • Two or three way valve.
  • Mea­sur­ing instru­ments.
  • Stop valve.
  • Fil­ter.
  • Bypass.

Depend­ing on the oper­at­ing con­di­tions, these ele­ments can be locat­ed in the imme­di­ate vicin­i­ty of the device, or at a decent dis­tance from it. Based on the con­nec­tion con­di­tions, there are:

  • Flex­i­ble har­ness. It is mount­ed on con­trol nodes locat­ed next to the device. The instal­la­tion of such strap­ping is con­sid­ered eas­i­er, since it makes it pos­si­ble to car­ry out all work on thread­ed con­nec­tions, with lit­tle or no need for weld­ing.
  • Rigid bind­ing. Used on devices that are remote from con­trol nodes and require strong com­mu­ni­ca­tions.

With a dif­fer­ence in the instal­la­tion tech­nique, both types per­form the same func­tion — they pro­vide set­ting and adjust­ment of the oper­at­ing mode of the heater.

Adjustment of the heating process

There are two ways to adjust the oper­at­ing mode:

  • Quan­ti­ta­tive. Adjust­ment is made by chang­ing the vol­ume of coolant enter­ing the device. With this method, there are sharp jumps in tem­per­a­ture, insta­bil­i­ty of the regime, there­fore, the sec­ond type has recent­ly been more com­mon.
  • Qual­i­ta­tive. This method allows you to ensure a con­stant flow of coolant, which makes the oper­a­tion of the device more sta­ble and smooth. At a con­stant flow rate, only the tem­per­a­ture of the car­ri­er changes. This is done by mix­ing a cer­tain amount of cold­er return into the for­ward flow, which is con­trolled by a three-way valve. Such a sys­tem pro­tects the struc­ture from freez­ing.

Features of installation and connection

Instal­la­tion work, con­nec­tion, sys­tem start-up, work set­up — all this should be done by a team of spe­cial­ists. Do-it-your­self instal­la­tion of a heater is pos­si­ble only in pri­vate homes, where there is no such high respon­si­bil­i­ty as in indus­tri­al premis­es. The main oper­a­tions include installing the device and con­trols, con­nect­ing them in the required order, con­nect­ing them to the coolant sup­ply and removal sys­tem, pres­sure test­ing, test run. If all nodes of the com­plex demon­strate high-qual­i­ty work, then the sys­tem is put into per­ma­nent oper­a­tion.

Rules of operation and the possibility of repair

The basic require­ments for the oper­a­tion and safe­ty of the device are set out in the pass­port. They are aimed at elim­i­nat­ing emer­gen­cies caused by exceed­ing the per­mis­si­ble tem­per­a­ture or pres­sure of the coolant, avoid­ing a sharp increase in the tem­per­a­ture of the com­plex dur­ing the first start-up in the cold sea­son. Par­tic­u­lar atten­tion should be paid to the risk of freez­ing of the tubes of the device in the win­ter, threat­en­ing the fail­ure of the device. To repair devices, spe­cial­ized orga­ni­za­tions should be involved; self-inter­ven­tion most often only increas­es the degree of the prob­lem.

Brief overview of modern models and prices

Sev­er­al mod­els can be con­sid­ered as exam­ples:

  • KSK‑3. Spi­ral-rolled heater with 3 rows of tubes. A com­mon domes­tic mod­el, test­ed and reli­able. The price of the device depends on its size, rang­ing from 5000 to 37$.
  • Vol­cano mini. Pol­ish device used to ser­vice rel­a­tive­ly small spaces. The cost is in the range of 20.000–30.000 rubles.
  • Gal­let­ti AREO. Ital­ian appli­ance equipped with a fan. Has attrac­tive appear­ance, dif­fers in low noise lev­el. At the same time, the prices for such devices are quite high and are at around 800 dol­lars and above.

The use of water heaters allows you to solve prob­lems with the prepa­ra­tion of sup­ply air, orga­nize space heat­ing. In addi­tion, devices are active­ly used in dry­ing instal­la­tions. Sim­plic­i­ty, unpre­ten­tious­ness in oper­a­tion and high prof­itabil­i­ty have made these devices lead­ers among indus­tri­al heat­ing instal­la­tions. Their long ser­vice life and the pos­si­bil­i­ty of being pow­ered from dif­fer­ent sources make them the most attrac­tive devices among all alter­na­tives.


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