Low Temperature Heating and Economic Efficiency
Today, increasingly low temperature heating Parallel to the developments in heating technology is gaining importance.
traditional water temperature in hot water central heating systems is valued at 90/70 ° C. Therefore, all descriptions, diagrams, tables, etc. are prepared according to these values. This value can be considered optimum temperature for conventional systems. However, low temperature, for example in floor heating water temperature does not exceed 55 ° C. boilers in Turkey coldest air of 65-70 ° C has been working at temperatures exceeding y.
heating with radiators in recent years there is a trend toward lower temperatures. In particular, natural gas cast iron boiler + double arises when it comes to these facilities. When coal or oil as fuel is used, why not further reduced acid corrosion in boiler water temperatures. In particular, steel corrosion in boilers pierces very quickly to reduce the smoke pipe and boiler life. Therefore, the higher the boiler water temperature (90 ° C) are kept in hot weather, water temperature, fuel economy sent three or four-way valve system to be short-circuited with water return is reduced. But these measures require expensive control systems. In addition, the yield will rise to the flue gas temperature of the boiler operating at high temperature will be reduced by an average 4%.
However, in case of burning natural gas instead of fuel corrosive acid that contains sulfur condensate corrosion due to high humidity it is important. The new generation of hot water boilers are designed to operate at low water temperatures. At the same time outside temperature boiler water temperature rises can be achieved without any mixing thermostatic controls to reduced fuel consumption. Thus, the control system can be used cheaper but more precise.
Boilers when 90/70 ° C instead of to 70/55 ° C hot water heating system is used to obtain the following advantages:
1. Depending on the low water temperature in the boiler flue gas in water with increasing temperature difference between the flue temperature is reduced and the boiler efficiency is increased. This will focus in particular on the rate of increase in productivity.
2. Low temperature thus increasing the feeling of comfort in heating.
3. Dust combustion of the curtain wall and processing and contamination problems are minimized. In contrast, low temperature heating will increase the initial cost of the system will increase the required radiator surfaces. However, this will be compensated by additional investments made fuel savings and additional investment will pay for itself after a while.
Economic efficiency of Low Temperature System
Low temperature 70/55 ° C heating provides for determining the yield increase was established theoretical model. This theoretical work in the same system 90/70 ° C controlled as 70/55 ° C was designed to be controlled again. sampled for a heating season (1960) hour outside temperature changes (from meteorological bulletins) an annual average efficiency of both systems is the amount of fuel oil a year, and considering a system is calculated.
In this account,
1. Construction of the project in terms of heat loss of 300,000 kcal / h, won the useful heat output of 315,000 kcal / h burner capacity and 355,000 kcal / h have been taken. As diesel fuel is used.
2. Automatic control is considered and selected the most suitable variation curve for each state.
3. Stop losses during cold weather, hot cider losses are considered incomplete combustion losses during each firing.
4. The increase in yield is taken into consideration, depending on the water temperature. According to calculations made as a result of annual fuel consumption:
a.90 / 70 ° C system 54 977 kg / year diesel
b.70 / 55 ° C “50 269 kg / year” was found.
The average annual yield of the system
a.90 / 70 ° C system at 74.1%
b.70 / 55 ° C “were 81.1%.
According to an annual fuel saving of 4,708 kg with a 7% increase in efficiency is achieved. The savings made will change naturally as conditions change. However, this account gives an idea as possible. In this system, a column heater cast radiator if it is considered used 90/70 ° C required for heating the surface of the system,
F = q / k.δt = 300,000 / (7,7.60) = 650 m2
70/55 ° C system temperature difference,
Dt = (70 + 55) / 2 = 20 is 42.5 ° C, the reduction in thermal capacity radiator,
q / QoE = (Dt / Δto) ^ n = (42.5 / 60) ^ 1.3
acceptable. Accordingly 70/55 ° C radiator surface required for the system,
F = has 1,000 m2. The difference needed extra radiator surface,
F = 1,000 to 650 = 350 m2
It is. Account history in the radiator price 17.5 $ / m² and the price of fuel $ 0.225 / kg is taken,
70/55 ° C system’s additional investment costs = 350 × 17.5 = $ 6,125
70/55 ° C system operating cost savings; = 4,708 x 0,225 = $ 1,059
Depreciation about time = 6125/1059 = 5.8 years
The result: even when using the most expensive radiator system is able to pay for itself in 5 years.
70/55 ° C Design of the system
70/55 ° C system in the design differs substantially heater tube diameters with the selection will account. 70/55 ° C system projecting MMO publication No. 84, which will be discussed to build on the heater design basis.
1. There is no change in heat loss calculations.
2. Heater selection:
The difference between the average water temperature in the room with the heater internal temperature 90/70 ° C and 60 ° C in the system as standard.
Δto = (90 + 70) / 2-20 = 60 ° C
This difference 70/55 ° C as standard in the system will be lower.
Dt = (70 + 55) / 2 – 20 = 42.5 ° C
thermal power of the radiators, depending on the temperature difference will be reduced as well. new thermal power depending on Δt’y,
q QoE (42.5 / 60) ^ n = qo.f
It can be expressed. Here,
q = Radiator 70/55 ° C in standard thermal power system
QoE = radiators 90/70 ° C system standard in thermal power, n = exponent coefficient.
These coefficients depending on the type of the heater varies between 1.2 and 1.3 and can only be found by experiment. n = 1,3 can be taken for radiators.
f = correction factor
correction factor for radiators, for the value of
f = (42.5 / 60) ^ 1.3 = 0.639
As it has. Radiator power company catalog is given to 90/70 ° C system, depending on the room temperature is multiplied by the value read from the catalog for factor 70/55 ° C has a radiator in the power system.
70/55 ° C system to determine the number of radiators now, that room heat loss, divided by the value for the relative heat loss is found. The value of the catalog number of the selected zone type radiator read.
For example, the room’s heat loss is 1000 kcal / h and the 221/500 column radiator is selected,
Relative heat loss = 1.000 / 0.639 = 1.565 kcal / h
Room temperature is approximately 22 ° C is read from the required number of 11 slices catalog.After calculating the required amount of radiators, radiator installation is the same.
3. Column chart and pipe diameters
Column schema exactly drawn. In the calculation of pipe diameters, in addition to the heat load of each pipe section column chart it is written in the mass flow rate of the pipe section. Mass flow,
m = Q / C. (TG-TC) = Q / 1 (70-55) = Q / 15 [kg / h]
Q = heat load of the pipe section [kcal / h ° C]
Example of 1,500 kcal / h with pipe flow rate of 100 kg / h value.
The only difference column in the table to fill the pipe and the pipe diameter calculation accounts for ruler determined the critical period after writing the fluid flow.
For example; 1500 kcal / h heat-carrying pipe at a flow of 100 kg / h is the çapı1 / 2 “from the table the tubing pressure loss, R = 2.6 mm WC / m, and velocity, V = 0.15 m / s is read. Special resistance coefficient and the constant presence of specific resistance.
4. boiler and boiler design to change.
5. Chimney account does not change
6. Expansion tank and pipes security account does not change
7. The circulation pump temperature difference increases the pump flow rate decreases because the account. Pump flow rate is also calculated by the same formula.
Source: Isısan Heating Installation Book