How a PAC Works
Heat Pump Internal Function
Client-friendly technical explainer for air-water PAC systems, all-in-one heat pumps, buffer tanks, ECS domestic hot water cylinders, serpentine boilers and the connection between heat pumps, floor heating, radiators and photovoltaic solar production.
Detailed PAC Technology Diagrams
Clean Systems Studio 3D-style schematic illustrations for explaining the internal PAC cycle, air-water architecture, buffer storage and ECS serpentine-coil principle.
1. PAC Refrigerant Cycle
The refrigerant absorbs outdoor heat, is compressed, transfers heat to water, then expands and repeats the cycle.
2. Air-Water PAC Architecture
Outdoor unit collects heat, hydraulic module transfers it to water, then water feeds circuits and ECS storage.
3. Buffer Tank / Ballon Tampon
The buffer tank adds water volume and separates PAC flow from building circuit flow when needed.
4. ECS Boiler with Serpentine Coil
The serpentine coil separates the PAC primary circuit from domestic hot water while transferring heat.
1. What is a PAC?
PAC means Pompe à Chaleur, or heat pump. A PAC is not a classical boiler. A boiler creates heat by burning gas, oil or using direct electric resistance. A PAC moves heat from one place to another. In an air-water system, it extracts heat from outside air and transfers it into a water circuit for heating and domestic hot water.
2. Mathematics & Physics of PAC Heat Transfer
A PAC / heat pump does not create all heat directly from electricity. It uses electrical energy to move existing thermal energy from the outside environment into the building. This is why the delivered heating capacity is expressed as kW thermal, while the compressor consumption is expressed as kW electrical.
Electrical input
The electrical input powers the compressor, fans, circulation pumps and controls.
Thermal output
The useful heat delivered to the house is thermal power, not electrical power.
Outside heat
The heat pump extracts heat from outside air, ground or water.
COP — Coefficient of Performance
The COP indicates how many kW of thermal heat are delivered for each kW of electrical input.
Example: if the PAC consumes 2 kW electrical and delivers 8 kW thermal, then:
This means that for every 1 kW of electricity, the PAC delivers 4 kW of heat. The remaining heat is extracted from the outside environment.
Practical example
If a house requires 10 kW of heat and the PAC operates at COP 4:
So the building receives 10 kW thermal, while the electrical installation supplies only 2.5 kW electrical.
Why COP drops in cold weather
The colder the outside source and the hotter the required heating water, the harder the compressor must work. This temperature lift is:
A low-temperature floor heating system at 35°C is easier for a PAC than old radiators requiring 55°C or more. This is why insulation, airtightness and a good PEB / EPB grade are essential before installing a PAC.
Carnot physics limit
The theoretical maximum COP is described by the Carnot relation. Temperatures must be expressed in Kelvin.
Example: with heating water at 35°C and outside source at 5°C:
Real machines have losses, so practical COP is lower, commonly around 3 to 5 depending on outdoor temperature, water temperature, defrost cycles and installation quality.
The heat pump delivers useful heat by combining electrical compressor energy with free environmental heat. For example, a 12 kW thermal PAC at COP 4 may consume only 3 kW electrical and extract 9 kW thermal from the outside environment.
3. Internal Refrigerant Cycle
Evaporator
Outside air transfers heat to the refrigerant. The refrigerant evaporates at low temperature.
Compressor
The compressor raises refrigerant pressure and temperature, making the heat usable for the building.
Condenser
The hot refrigerant transfers heat to the water circuit through a heat exchanger.
Expansion Valve
The refrigerant pressure drops, temperature falls, and the cycle starts again.
4. Buffer Tank / Ballon Tampon
A buffer tank is a water volume installed between the PAC and the heating circuits. It helps stabilize flow, reduce short cycling and improve hydraulic separation when the building has several circuits or zones.
5. All-in-One PAC System
| Element | Role | Client explanation |
|---|---|---|
| Outdoor unit | Collects heat from outside air. | The external machine with fan and refrigerant circuit. |
| Indoor hydraulic module | Transfers heat into water and controls heating operation. | The technical interface between PAC and building. |
| Integrated ECS cylinder | Stores domestic hot water. | Hot water for showers, kitchen and sanitary use. |
| Smart controls | Schedules heating, ECS and efficiency modes. | Allows better comfort and self-consumption strategy. |
6. ECS Boiler / Domestic Hot Water Cylinder
ECS means Eau Chaude Sanitaire, or domestic hot water. The PAC can heat a storage cylinder for showers, sinks and kitchen use. The cylinder size depends on occupants, comfort level, bathrooms and peak hot water demand.
7. Boiler with Serpentine Coil / Boiler avec Serpentin
A serpentine boiler or cylinder contains a coil heat exchanger inside the tank. The PAC heats water or fluid in the coil, and the coil transfers heat to the stored domestic water. This keeps the heating circuit and sanitary water separated.
8. PAC + Solar Self-Consumption Logic
Photovoltaic panels produce electricity during daylight hours. A smart PAC + Solar strategy tries to use part of this electricity for heating, ECS production, thermal storage or future battery integration.
9. Client Questions & Simple Answers
Manufacturer Reference Documentation
This section collects the technical manufacturer documentation required before final PAC selection. It supports the Systems Studio study workflow, but does not replace installer validation, manufacturer sizing software, warranty conditions or local electrical/hydraulic compliance checks.
BEMCO Installation File
Main BEMCO installation reference file for technical study, installer coordination and project preparation.
Open installation fileAll-in-One PAC System
Compact indoor unit documentation with integrated ECS cylinder, hydraulic module, backup heater, controller, dimensions and service clearances.
Open All-in-One catalogBuffer Tank / Ballon Tampon
Buffer tank volume tables, hydraulic separation diagrams, anti-cycling recommendations, defrost support notes and installation positions.
Open buffer tank catalogECS Boiler / Domestic Hot Water Cylinder
Storage volume, recovery time, insulation losses, electric backup heater, legionella cycle, sanitary connection and maintenance requirements.
Open ECS boiler catalogFloor Heating / Chauffage Sol
Floor-heating construction, water temperature, manifold logic, tube circuits and low-temperature PAC compatibility.
Open floor-heating catalogInfloor Radiant Heating Guide
Radiant floor-heating documentation for Infloorboard, concrete, Gypcrete, RadiantTrak, tubing, manifolds, hydronic calculations and LoopCAD support.
Open Infloor guideEcopure MP Warmtepomp
BEMCO Ecopure MP heat pump documentation for PAC model comparison and pre-selection.
Open Ecopure MP catalogEcopure M Heat Pump
BEMCO Ecopure M documentation for model range, capacity review and project suitability.
Open Ecopure M catalogEcopure P Heat Pump
BEMCO Ecopure P documentation for model range, heating capacity, hydraulic and electrical study.
Open Ecopure P catalogEcopure S Heat Pump
BEMCO Ecopure S documentation for model range, capacity pre-selection and project comparison.
Open Ecopure S catalogHydraulic Safety Components
Expansion vessel, pressure relief valve, air separator, dirt separator, magnetic filter, circulation pump, mixing valve and manifold documentation.
Per project / supplierProject-Specific Installer Quotes
Final contractor quotations, selected PAC model, selected tank volume, installation scope, electrical scope, commissioning checklist and warranty terms.
Per project