What temperature is the most energy-saving gas wall-mounted boiler set at?
At present, there is a saying in the market that the gas wall-mounted boiler temperature is set at the highest temperature to be the most energy-efficient. Floor heating temperature set at 40 ℃ is the least energy efficient. This statement sounds reasonable, but it is very one-sided. It only looks at the conclusion that the wall-mounted boiler works at the maximum load and the minimum load, and the actual operating conditions are not set at the highest temperature. It has been working at full load, and has been working under minimum load when it is set at the minimum temperature. Only when the three conditions of working heat load, efficiency and working time are determined, energy saving can be compared.
We only discuss the performance of gas wall-mounted boilers (fixed speed fans) that generally reach the European three-star certification, 24kW gas-fired wall-mounted boilers, the maximum pressure after the valve is 110mmH2O, and the minimum pressure after the valve is 8mmH2O.
A. Briefly introduce the requirements of the European three-star certification. The EU Energy Efficiency Directive 92-42-EEC specifies the energy efficiency index requirements for gas-fired wall-mounted boilers as shown in the table below, and the star-level logo is implemented.
Because the wall-mounted boiler works under partial load most of the time during the heating process in winter, the requirement for its efficiency is not only at full load, but the thermal efficiency under 30% load is very important.
It is very difficult to get a three-star or four-star certification, especially the efficiency at 30% load. It particularly emphasizes the overall design of the wall-mounted boiler – combustion system, heat exchange system, smoke exhaust system, etc.
B. It is necessary to realize that ordinary gas-fired wall-mounted boilers have the highest efficiency at full load and low efficiency at partial load. For gas-fired wall-mounted boilers that meet the Samsung certification, at full load and 30% load The efficiency difference is around 3%. There is no direct relationship between full-load operation and temperature setting. If you set 80 degrees, the full-load working time will be longer, and if you set 40 degrees, the full-load working time will be shorter, but these are related to the initial state of the system.
C. The heat loss of gas-fired wall-mounted boilers is mainly the emission of high-temperature flue gas, and the exhaust gas temperature and excess air coefficient have a great influence on the efficiency. In order to achieve the purpose of energy saving, it is necessary to reduce flue gas emissions, that is, to reduce the heating working time of gas-fired wall-mounted boilers.
D. It can be seen from the above B and C that in order to achieve the best energy-saving purpose while meeting the heating requirements, we need the gas wall-mounted boiler to work at full load as much as possible, and stop when the temperature requirements are met. Therefore, the following topics are brought up:
a. Minimum output power for heating: At present, the minimum output power of many manufacturers’ wall-mounted boilers for heating is adjustable, which can be from 0% to 80%. The minimum output power of heating can be adjusted to about 70%. Basically, the pressure behind the valve is 110*0.72=54mmH2O. No matter the set temperature is 80 or 40 degrees, the wall-mounted boiler will work at full load first, and when the set temperature is reached, the flame adjustment and Adjust from 110 to 54mmH2O, and there is no need to adjust the flame from 110 to 8mmH2O in the state of sanitary hot water, because sanitary hot water needs a stable outlet temperature, and the heating temperature curve does not need to be very stable, just zigzag . When it reaches the set temperature, it will stop and restart when the temperature drops to 77 or 37 degrees. Generally, it will work together with the three-minute delay of heating.
b. A very important point is the matching requirements of the heating system: the system resistance should not be very large, and the flame should be adjusted from 110 to 54mmH2O (24-16.8 kW). If the system resistance is large, the heating system flow and flow rate Low, the water temperature rises quickly, the heat is not taken away, the temperature sensor senses the temperature quickly reaches the set temperature and shuts down, which will cause the wall-mounted boiler to start frequently (it will start after 3 minutes), which is also very unfavorable. Therefore, it is required that the radiator system needs to be connected in parallel with two pipes (same route or different route), and a large floor heating system needs to be equipped with a coupling tank or a hydraulic balancer, a water mixing valve and a water pump.
The efficiency difference between full load and 30% load of gas-fired wall-mounted boilers that have not reached the Samsung certification is larger, generally within 5%. In the case of increasing the minimum output power of heating, the wall-mounted boiler can be The boiler works at full load or close to full load, and waits after reaching the set temperature to achieve the purpose of energy saving.
In short, ordinary gas-fired wall-mounted boilers can achieve the purpose of energy saving at any set temperature. After all, the loss of gas-fired wall-mounted boilers is only the loss of flue gas, and there is no heat loss from the pipe network and the equipment itself, which saves energy. The effect is very obvious.
At present, the domestic market has begun to promote the use of condensing gas-fired wall-mounted boilers, especially the fully premixed condensing wall-mounted boilers, which are favored by more and more people. Due to the use of new technology, the condensing gas-fired wall-mounted boiler has an efficiency of about 108% under partial load and full load conditions (the temperature of supply and return water is 50°C to 30°C). This kind of wall-mounted boiler is especially suitable for low-temperature floor heating, the supply and return water temperature is low, and its condensation effect is good. If the water temperature is set at 80 ℃ ~ 60 ℃, the efficiency is about 98%.
