Hot water boiler heating

Let’s see the actual situation. . . Generally, the atmospheric pressure hot water boilers we produce have a ratio of 85/60

Thank you! :handshake:handshake:handshake

It’s not just the temperature difference between the supply and return water in heating hot water boilers; flow rate, pressure, and area also play a role

It is a 20-story inpatient building in a hospital covering an area of 65,000 square meters, located in Hunan Province. How should the heating requirements and water pump flow rates per square meter be calculated? Thank you!

The temperature of the heating water supply and the temperature difference are determined by the terminal heating devices; in the case of radiators, the temperature is usually around 71 degrees, with a temperature difference of 20–25 degrees； For underfloor heating, the supply water temperature is usually around 60 degrees, with a temperature difference of 10 degrees. The calculation of the water pump’s flow rate is also related to the heating terminal equipment, as different required temperature differences result in different calculations for the water pump’s flow rate.

65,000 square meters multiplied by the unit heat load gives the required boiler output. Hospitals typically have a heat load of 65–80 W/㎡, which means the required power is around 5,000 kW. However, it’s not possible to use just one boiler; if two boilers are used, each one should operate at no less than 70% of its maximum capacity, 35% for three boilers, and 25% for four boilers. With a height of 20 floors, it is 20*2.8m=56m, so a hot water boiler capable of withstanding high pressure is required. Choose a water pump with a capacity corresponding to the flow rate; head usually refers to the maximum height that the pump can lift water to, and is denoted by H. The most commonly used formula for calculating the head of a water pump is H=(p2-p1)/ρg+(c2-c1)/2g+z2-z1. Here, H is the head, in meters; p1 and p2 are the pressures of the liquid at the inlet and outlet of the pump, in Pa; c1 and c2 are the flow velocities of the fluid at the inlet and outlet of the pump, in m/s; z1 and z2 are the heights at the inlet and outlet, in meters; ρ is the density of the liquid, in kg/m3; g is the acceleration due to gravity, in m/s2. Centrifugal clean water pumps with a specific speed of ns between 130 and 150 are generally selected. The flow rate of such pumps should be 1.1 to 1.2 times the rated flow rate of the chiller unit (1.1 for a single pump, and 1.2 when two pumps are used in parallel). As an estimate, the friction loss per 100 meters of pipe length can be taken as 5 mH2O. The formula for calculating the pump head in mH2O is: Hmax = ΔP1 + ΔP2 + 0.05L(1+K), where ΔP1 represents the water pressure drop in the evaporator of the chiller. △P2 is the pressure drop of the unit with the greatest water pressure loss among the air-conditioning terminal units connected in parallel in that loop. L is the length of the most unfavorable loop, while K is the ratio of the sum of the equivalent lengths of local resistance in that most unfavorable loop to the total length of the straight sections. When the most unfavorable loop is long, the value of K ranges from 0.2 to 0.3; when it is short, the value of K ranges from 0.4 to 0.6. After reviewing the formula for calculating pump head, I believe everyone now has a fairly comprehensive understanding of how to determine pump head. In general, the head of a water pump is calculated using Bernoulli’s equation.

For heating with atmospheric-pressure hot water boilers, it is necessary to maintain the room temperature once the radiators have been selected. Centralized management of the boiler room system is required; high-temperature heating can be employed if water treatment is in place (supply water temperature: 90°C, return water temperature: 60°C)； In the absence of water treatment, low-temperature heating can be used (outlet temperature 80/return temperature 50).