5 minutes 60.3k.

For the correct selection of the necessary equipment, it is enough to know: the required power of the air heater, which will subsequently be mounted in the supply ventilation heating system, the air temperature at its outlet from the air heater installation and the coolant flow rate.

To simplify the calculations made, an online calculator for calculating the basic data for the correct selection of a heater is presented to your attention.

With it, you can calculate:

1. Thermal power of the heater kW. In the fields of the calculator, enter the initial data on the volume of air passing through the heater, data on the temperature of the air entering the inlet, and the required temperature of the air flow at the outlet of the heater.
2. outlet air temperature. In the appropriate fields, you should enter the initial data on the volume of heated air, the temperature of the air flow at the inlet to the installation and the heat output of the heater obtained during the first calculation.
3. Coolant consumption. To do this, enter the initial data into the fields of the online calculator: the thermal power of the installation obtained during the first calculation, the temperature of the coolant supplied to the inlet to the heater, and the temperature value at the outlet of the device.

Calculation of heater power

Calculation of the coolant flow

The calculation of heaters, which use water or steam as a coolant, occurs according to a certain method. Here, an important component is not only accurate calculations, but also a certain sequence of actions.

Note!

## Calculation of performance for heating air of a certain volume

Determine the mass flow of heated air

G (kg/h) = L X R

where:

L — volumetric quantity of heated air, m3/hour
p — air density at an average temperature (divide the sum of the air temperature at the inlet and outlet of the heater by two) — the table of density indicators is presented above, kg / m.cube

We determine the heat consumption for heating the air

Q (W) = G X c X (t con — t beginning)

where:

G — mass air flow, kg/hour s — specific heat capacity of air, J/(kg•K), (the indicator is taken from the incoming air temperature from the table)
t nach — air temperature at the inlet to the heat exchanger, °С
t con — the temperature of the heated air at the outlet of the heat exchanger, °С

## Calculation of the frontal section of the device required for the passage of the air flow

Having determined the required thermal power for heating the required volume, we find the frontal section for the passage of air.

Frontal section — working internal section with heat-releasing tubes, through which flows of injected cold air directly pass.

f (sq.m.) = G / v

where:

G — mass air flow, kg/hour
v — mass air velocity — for finned heaters is taken in the range of 3 — 5 (kg / m.kv•s). Permissible values ​​— up to 7 — 8 kg/sq.m.s

## Calculation of Mass Velocity Values

We find the actual mass velocity for the calorific installation

V(kg/sq.m.s) = G / f

where:

G — mass air flow, kg/h
f — area of ​​​​the actual frontal section taken into account, sq.m.

## Calculation of the coolant flow in the calorific installation

We calculate the flow rate of the coolant

gw (kg/s) = Q / ((cw X (t in — t out))

where:

Q — heat consumption for air heating, W
cw — specific heat capacity of water J/(kg·K)
t in — water temperature at the inlet to the heat exchanger, °C
t out — water temperature at the outlet of the heat exchanger, °C

## Calculation of the speed of movement of water in the pipes of the heater

W (m/sec) = gw / (pw X fw)

where:

gw — coolant flow rate, kg/s
pw — density of water at an average temperature in the air heater (accepted according to the table below), kg / m3
fw — the average area of ​​​​the free section of one pass of the heat exchanger (accepted according to the table for the selection of heaters KSK), m.kv

## Determination of the heat transfer coefficient

The coefficient of thermal efficiency is calculated by the formula

Tow / (m.cube x C) = BUT X Vn X Wm

where:

V — actual mass velocity kg / m.kv x s
W — the speed of movement of water in pipes m / s
A

## Calculation of the thermal performance of the calorific unit

Calculation of the actual heat output:

q (W) = K X F X ((t in +t out)/2 — (t start +t con)/2))

or, if the temperature difference is calculated, then:

q (W) = K X F X average temperature difference

where:

K — heat transfer coefficient, W/(m.kv•°C)
F — heating surface area of ​​the selected heater (accepted according to the selection table), sq.m.
t in — water temperature at the inlet to the heat exchanger, ° С
t out — water temperature at the outlet of the heat exchanger, °С
t nach — air temperature at the inlet to the heat exchanger, °С
t con — the temperature of the heated air at the outlet of the heat exchanger, °С

## Determining the margin of the device by thermal power

We determine the margin of thermal performance:

((qQ) / Q) x 100

where:

q — actual thermal power of selected heaters, W
Q — calculated thermal power, W

## Calculation of aerodynamic drag

Calculation of aerodynamic drag. The amount of air loss can be calculated using the formula:

ΔРa (Pa)=AT X Vr

where:

v — actual mass air velocity, kg/m.kv•s
B, r — the value of the module and degrees from the table

Helped me understandDidn’t work, needs more explanation

## Determination of the hydraulic resistance of the coolant

The calculation of the hydraulic resistance of the air heater is calculated by the following formula:

∆Pw(kPa)= FROM X W2

where:

FROM — the value of the coefficient of hydraulic resistance of a given model of the heat exchanger (see the table)
W — the speed of water movement in the tubes of the air heater, m / s.