A heat-pump project is not defined by the electrical rating on a nameplate. Its case turns on the heat actually delivered, the temperature lift, seasonal efficiency and the role of any boiler or resistance backup. The baseline must therefore describe the former generator and the distribution system before removal. RES060, TER040, TER100, IND040 and IND060 may be useful starting points, but their current official wording decides which route, variables and records apply.
Choose the heat-pump case, not merely the machine
A domestic monobloc replacing a gas boiler, a packaged rooftop unit replacing direct expansion equipment and an industrial high-temperature machine solve different problems. Identify heating, cooling and domestic-hot-water services separately, then test the sector, former technology and capacity boundaries attached to each candidate code. Tie each candidate route to a distinct equipment schedule so hybrid and all-electric configurations are not conflated.
SCOP is seasonal and climate-dependent, whereas COP describes a selected test point. Product literature may list several climates and water outlet temperatures. The dossier must choose the value allowed by the applicable sheet and link it to the installed model, emitters and control setting rather than selecting the most flattering table column. Confirm the declared climate bin and outlet-temperature application before carrying the manufacturer value into the calculation.
Reconstruct loads and temperatures before removal
Record fuel invoices, burner tests, boiler efficiencies, weather-compensated flow temperatures and occupied schedules before disconnection. A radiator circuit requiring 70 degrees Celsius cannot be represented as low-temperature underfloor heating. The former generator serial number and served zones also prevent unrelated loads from entering the comparison. Where invoices cover several generators, apportion consumption from metering or a documented engineering balance rather than floor area alone.
Heat loss, peak demand and annual useful heat answer different questions. Oversizing from the peak alone can cause cycling at mild conditions, while undersizing transfers winter hours to auxiliary heat. A load-duration view shows how often each compressor stage, immersion heater or retained boiler is expected to operate. Plotting backup contribution on the same duration curve makes the assumed seasonal share auditable.
Use SCOP and hybrid operation coherently
For a bivalent installation, define the changeover temperature, control hierarchy and metering boundary. Savings cannot be calculated as if the heat pump supplied all demand when the boiler remains active. Fuel and electricity assigned to backup should follow the same operating calendar and thermal service boundary. The metering plan should separate compressor, immersion heater, circulation and retained-boiler energy wherever the method requires it.
Domestic hot water needs its own storage losses, hygiene temperatures and recirculation treatment. If one machine also cools, allocate electricity consistently and avoid crediting free-cooling or control improvements twice. The authorised formula, units and seasonal factors in the selected PDF override a bespoke sales model. Use a consistent useful-heat boundary when allocating shared compressor electricity between space heating, hot water and cooling.
Commissioning records that explain performance
Commissioning should capture refrigerant circuit checks, hydraulic balancing, flow and return temperatures, electrical protection, sensor placement and enabled weather compensation. Trend data during cold and mild days can reveal short cycling or simultaneous heating and cooling that a completion photograph would never show. Acceptance criteria should include stable flow, achievable emitter temperatures and correct changeover operation under representative demand.
Match purchase order, invoice, model identifiers, capacity, installer declaration and site photographs. Preserve images of the former boiler plate, fuel connection and distribution arrangement. For split systems, indoor and outdoor serial numbers must be paired so that the evidence describes one installed system rather than two catalogue products. Record firmware and controller settings alongside serial numbers because identical hardware can deliver materially different seasonal operation.
Decide with defrost, backup and uncertainty visible
Defrost energy, crankcase heaters, circulation pumps and standby consumption matter particularly in marginal climates and low-load buildings. Noise restrictions or a weak electrical connection may also change the final design. Document these constraints because an unrecorded design revision can invalidate the original seasonal calculation. An electrical-capacity check should cover starting current, auxiliary heaters and any network reinforcement included in the final design.
The investment decision should compare total operating cost and resilience, not treat an estimated CAE quantity as guaranteed income. Confirm the current sheet, annexes and transitional provisions immediately before submission; verification may accept a lower saving or reject a baseline that cannot support the claimed hybrid operating share. The reference codes for this review are RES060, TER040, TER100, IND040 and IND060. Show low, central and adverse seasonal cases so the project remains viable if backup operation exceeds the design estimate.