The allocation of central air-conditioning and heating costs is a long-standing flashpoint between office building managers and tenants. This article documents a tenant submetering retrofit in a Grade-A office tower in South China: from area-based apportionment with constant disputes to per-tenant metering and transparent billing. In the first year after the retrofit, comprehensive energy use per unit area fell by about 15 percent, and billing disputes dropped by roughly 90 percent. All figures in this article have been anonymized per the client's request.
The Grade-A office tower in South China has 28 floors above ground, a gross floor area of about 85,000 square meters, and was delivered in 2016. It houses more than 60 tenants spanning finance, law, and technology. Cooling is provided by centralized electric chillers, winter heating comes from district heat, and the terminals are mostly fan-coil units with fresh-air systems. Since delivery, air-conditioning cooling charges and winter heating fees had been apportioned strictly by leased area. Disputes erupted in 2024: high-density tenants argued that their actual consumption far exceeded their apportioned share yet they overpaid by area, while flexible-work tenants objected to paying for operating hours when their spaces sat empty. The property team handled over 40 such complaints per quarter, some tenants deferred property fees on these grounds, and occupancy slipped to 88 percent. In the second half of 2024, the owner commissioned a submetering retrofit with a clear goal: without changing the terminal form, achieve per-tenant metering, consumption-based billing, and publicly verifiable data.
The retrofit faced three practical constraints. First, zero data foundation: the building had no submetering devices at all, only whole-building master-meter readings, so the pre-retrofit energy profile of each floor was unknown and design had to proceed without baseline data. Second, highly varied tenant profiles: more than 60 tenants with different operating hours, staffing densities, and overtime intensity required a metering and billing scheme that accommodates both high-load tenants and flexible-work tenants fairly. Third, no disruption to daily operations: with the building in full use year-round, branch metering devices could only be installed on weekends and at night, with no more than a four-hour window per tenant area, demanding plug-and-play devices and minimal pipe downtime.
The retrofit proceeded in three steps: per-tenant metering, edge aggregation, and transparent billing. Step one, per-tenant metering: ZYH-542 ultrasonic heat meters applied to cooling and heating metering for office tenant submetering were installed on the return pipes of each tenant's air-conditioning water branch, one floor and one tenant at a time, enabling independent per-tenant measurement of cooling and heating energy with a 15-minute metering interval; in parallel, temperature and humidity transmitters deployed for tenant-area room monitoring and billing verification in office buildings were placed at representative points in tenant areas as a fairness check for billing, so tenants can compare their own bills against room-temperature curves and confirm that metering matches actual usage. Step two, edge aggregation: floor-level metering devices connect via RS-485 buses to ECG100 edge data managers applied to submetering data aggregation and offline buffering, which aggregate per-floor data, buffer it locally during network outages, and resume transmission afterwards; data is then uploaded to the property's energy management platform through energy consumption gateways for centralized collection and protocol conversion of many metering loops, and the platform auto-generates per-tenant bills. Step three, transparent billing and operational optimization: tenants can query their own 15-minute energy curves and bill composition through a client portal; on the property side, ECC200 network controllers optimizing chiller and pump schedules based on per-tenant load eliminate the old run-everything-at-once pattern, while common-area energy is metered separately, apportioned by area, and published.
The year 2025 is the first full operating year after the retrofit, with results verified as follows.
| Metric | Before (Year 2024) | After (Year 2025) |
|---|---|---|
| Cooling and heating cost allocation | Apportioned by leased area, no submetering data | Per-tenant consumption-based billing; common areas apportioned by area and published |
| Billing-related disputes (monthly average) | Over 40 | Below 5, down about 90 percent |
| Comprehensive energy use per unit area | About 95 kWh per square meter per year | About 81 kWh per square meter per year, down about 15 percent |
| Tenant energy visibility | No data available | 15-minute per-tenant energy curves, bills publicly verifiable |
| Billing cycle | Quarterly manual accounting, lagging about two months | Monthly automated billing, error rate under 1 percent |
With a total retrofit investment of about 1.8 million yuan, and factoring in lower dispute-handling costs and recovered occupancy, the static payback period is about 3.5 years. By the end of 2025, occupancy had climbed back above 95 percent. The owner has connected submetering data to the annual energy audit and plans to offer tenants energy-saving recommendations based on their consumption profiles, moving toward refined energy operations.
