Current Billing Methods for Central Air Conditioning

1. Billing by Area: Users are charged a unit price based on their actual floor area, regardless of their actual usage.

   • Calculation method: User cost = Unit price per area * User's floor area.

2. Billing by Usage Time: The operating time of terminal equipment, such as the valves and fans of fan coil units, is accumulated to determine the user's consumption.

   • Calculation method: User cost = Unit time price * User's usage time * Terminal weighting coefficient.

3. Billing by Usage (Energy) Volume: The energy used by the terminal unit of the central air conditioning system is measured. The user's consumption is essentially the amount of heat exchanged between the terminal coil and the room air. By measuring the temperature difference between the inlet and outlet water of the terminal unit and the water flow rate, the amount of heat exchanged can be calculated.

   • The calculation formula is (1):

     text

     Q = ∫ qm * Δh dt = ∫ qv * ρ * Δh dt

     Where:

     • Q — Heat released or absorbed (J or wh);

     • qm — Mass flow rate of water passing through the heat meter (kg/h);

     • qv — Volumetric flow rate of water passing through the heat meter (m³/h);

     • ρ — Density of water passing through the heat meter (kg/m³);

     • Δh — Enthalpy difference of water between the inlet and outlet temperatures of the heat exchange system (J/kg);

     • t — Time (h).

   • Energy-based billing method: User cost = Energy unit price * User's energy consumption.

Analysis of Current Billing Methods for Central Air Conditioning

1. Billing by Area: This method is very unfair to users who do not use the central air conditioning. It does not encourage energy-saving awareness among users and leads to significant waste.

2. Billing by Time: As users' awareness of their rights has increased, people have questioned area-based billing, leading to the gradual emergence of time-based billing. This method is relatively more reasonable than area-based billing, as users are only charged when they use the system. However, it has the following issues:

   • 2.1 Cumulative usage in time-based billing is an estimate under specific test conditions: In principle, time-based billing calculates the cumulative operating time of the terminal unit. It may seem to consider factors like the cooling capacity of the terminal unit and the status of the main unit, but the actual operating conditions of fan coil units are vastly different from fixed laboratory conditions. Taking fan coil units as an example: while manufacturers provide cooling capacity parameters, these are determined under fixed laboratory conditions. Using a fixed value to calculate a dynamically changing actual value is clearly unreasonable. Changes in ambient temperature and humidity (heat sources), variations in chilled water inlet temperature due to changes in the main unit's operation, and the resulting changes in actual cooling capacity make it difficult to achieve a standard, quantifiable measure. Particularly, changes in ambient temperature and humidity are directly related to the user's thermal load. Therefore, simply relying on so-called weighting coefficients for fan coil units to address the shortcomings of time-based billing is impractical.

   • 2.2 Legitimacy of Time-Based Billing: Can time-based billing serve as the definitive "scale" for central air conditioning billing systems? Looking at water, electricity, and gas billing, the basis for charges are relevant metering devices – water meters, electricity meters, and gas meters act as the "scales" for these industries, with strict requirements and oversight under metrology laws. So, can time-based billing be the "scale" for the air conditioning industry? The answer is no. Due to its fundamental flaws, time-based billing is merely an estimate of user consumption. In practice, it has replaced area-based billing and eliminated the unreasonable phenomenon of charging users even when they don't use the system. However, as a metering "scale," it falls far short. It cannot provide accurate quantification of user consumption and therefore lacks the necessary legal foundation. This is the current state of time-based billing.

3. Energy-Based Billing:

   • 3.1 Heat Meters as the "Scale": To standardize the central heating and cooling industry and promote energy conservation, relevant regulations and standards have been gradually introduced. First, the standard CJ128-2000 for heat meters measuring heating and cooling quantities was issued, later revised to CJ128-2007. Subsequently, the national standard GB/T32224-2015 for heat meters was released, specifically describing and setting requirements for cooling measurement similar to central air conditioning. The General Administration of Quality Supervision, Inspection and Quarantine also established the metrological verification regulation JJG225-2001 for heat/cool meters to standardize their metrological requirements, establishing heat meters as the "scale" for central heating and cooling. Because heat meters can truly quantify user consumption, they genuinely protect users' practical interests. Adhering to the principle of "pay more for more usage, pay less for less usage" enhances users' energy-saving awareness and achieves environmental goals.

   • 3.2 Current State of Heat Meter Products: While understanding the rationale of heat meters, one might question the current state of heat meter products. Are they mature? Are they stable in engineering applications? Heat meters have been used abroad for decades. Domestically, numerous manufacturers began entering this field twenty years ago. However, due to unfamiliarity with the application characteristics of heat meters, such as water quality requirements and operating environments, the initial application of these products was not very successful. Issues related to quality or application arose, leading to billing failures – for example, poor water quality causing flow meter failure, or condensation forming on calculators damaging the devices. With accumulating application experience, some manufacturers have gained considerable successful experience. For instance, BASIC CONTROLS, through over twenty years of experience in central air conditioning billing systems and understanding of air conditioning water quality, has designed flow meters specifically for air conditioning measurement with excellent anti-clogging characteristics, making them particularly suitable for poorer water conditions. These have gained recognition from many users in practical applications. Furthermore, issues like condensation and moisture in air conditioning environments have been properly addressed through continuous efforts. In terms of billing, considerations for domestic applications have led to added features like time-of-day billing and holiday billing schedules. These developments have made energy-based air conditioning billing increasingly mature and reliable.

In summary: Billing by area is a seemingly simple but traditional and unscientific method. Billing by time is a transitional method between energy-based and area-based billing. Energy-based billing is currently the most scientific and reasonable method and has become the mainstream approach for central air conditioning system billing.