Buffer tanks for aerothermal systems in Madrid: installation and maintenance
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The inertia tank —also known as a buffer tank or hydraulic accumulator— is a key component in heat pump aerothermal systems. Its main function is to provide a guaranteed minimum volume of water in the heating circuit so that the compressor of the pump does not experience excessively frequent stops and starts (short cycles). Each start of the compressor subjects the equipment to a peak current and mechanical stress that, when accumulated, drastically reduces its lifespan. With the appropriate volume of inertia, the compressor operates in longer cycles and at variable load, resulting in a higher COP and equipment that can exceed 15 years of lifespan.
The capacity of the tank is calculated based on the power of the heat pump and the flow rate of the installed hydraulic circuit. As a reference, manufacturers usually require a minimum volume of 15-20 liters per kW of heating power. In practice, the most common tanks in single-family homes in Madrid range from 50 to 200 liters: 50-80 L for systems up to 8 kW, 100-150 L for units of 10-16 kW, and 200 L for larger systems or those with complex hydraulic circuits. Incorrect installation or the absence of the tank may void the manufacturer's warranty.
At Uniclima, we manage the entire process:
- Calculation of the required volume according to the power of the equipment and the actual flow rate of the existing circuit.
- Model selection compatible with your heat pump (Daikin Altherma, Mitsubishi Ecodan, Saunier Duval Galis, Ariston Nimbus or other brands).
- Hydraulic installation: flow and return connections, air vents, shut-off valves, draining and filling of the circuit with treated water.
- Integration with the controller of the heat pump for the correct management of temperatures and priorities.
- Circuit check: filling pressure (1-1.5 bar), air bleeding and leak tightness verification before commissioning.
Frequently Asked Questions
Is the buffer tank mandatory in all aerothermal systems?
Not in all, but in most residential installations. Manufacturers like Daikin and Mitsubishi specify in their technical manuals the minimum water volume in the circuit to ensure the proper functioning of the compressor. If the underfloor heating circuit or fan coils already have sufficient volume (which often occurs in large installations), the tank may not be necessary. We verify this by measuring the flow rate and the actual volume of the circuit during the pre-installation visit.
What tank capacity do I need for my installation?
The general rule is 15-20 litres per kW of installed heating power. A heat pump of 8 kW requires between 120 and 160 litres of total volume in the circuit (tank + pipes + emitters). If your radiators or underfloor heating already provide that volume, the additional tank can be 50 litres to cover the margin. For units of 12-16 kW, tanks of 100-200 litres are common. We provide the exact figures after reviewing the plans of your installation or taking measurements on site.
Does the buffer tank also work for DHW?
No. The inertia tank is a closed circuit accumulator for heating: the water it contains circulates only through the internal hydraulic circuit and never comes into contact with the domestic hot water. For DHW, a solar accumulator or an independent buffer tank with a coil is used, equipped with a magnesium anode and a legionella prevention function. They are distinct elements with different functions, although they can be integrated into the same system and managed by the same heat pump controller.