The installation market is witnessing a veritable boom in heat pumps . Gas prices and concerns about its availability force us to look for alternative heating devices powered by energy from other sources. The costs of purchasing a heat pump are still not among the lowest, but these devices pay for themselves over time through cheap operation, and they are also maintenance-free. However, the efficiency of a heat pump also depends on the refined, properly selected components of the installation. The buffer tank plays a special role in its proper operation.
This article will explain to you:
- difference between a hot water tank and a buffer tank;
- the role of each of them in the heat pump heating system;
- ways of connecting buffer tanks and the advantages of each of them.
Special features of the Roth Thermotank Quadroline for heat pumps
Roth's production experience dates back to the 1970s. In 1971, the production of polyethylene tanks for heating oil was launched, based on the blown extrusion technology. The process of manufacturing polyethylene products, perfected for over 50 years, is still used today. The machinery park, supported by modern control, and the extensive experience of the engineering staff made it possible to overcome a barrier that seemed insurmountable for a long time - the steel structure of the tanks gave way to plastics .
The material used to manufacture Roth Thermotank Quadroline heat pump tanks is a composite of HDPE (PE-RT), an aluminum anti-diffusion layer and glass fiber . 100% diffusion resistance thanks to the aluminum protective coating is confirmed by the certificate of the German Fraunhofer IKTS Hermsdorf Institute.
Roth Thermotank Quadroline tanks are available in three capacities: 325, 500 and 850 l, as buffer tanks for central heating (TQ-P), buffer tanks with hydraulic clutch (TQ-T), coil tanks for domestic hot water (TQ-TW), coil tanks for domestic hot water with combi buffer (TQ-TWK and TQ-TWT) and solar (TQ-S, TQ-TWS, TQ-K). The tanks provide resistance to constant pressure of 3 bar and max. short-term operating temperature of 90° C , and long-term 80° C.
The Roth Thermotank Quadroline body is covered with EPS insulating segments, creating a square construction profile that allows for the optimal use of every square centimetre of surface. The compact, practical shape of the tanks, weighing only about 1/3 of a comparable conventional steel tank , limits the amount of space needed in the room to a minimum. The energy efficiency class of Roth buffer tanks and domestic hot water tanks, depending on the Thermocoat plus or Thermocoat thermal jacket used, is at level A or B, respectively.
The role of the buffer tank in a heat pump system
The heat pump compressor is a sensitive and delicate component. It reacts negatively to frequent switching on and off, and its service life depends on a correctly designed and executed installation system. The heat pump needs about 5 minutes in the start-up cycle to self-regulate, and then consumes a lot of electricity. The optimization of the heat pump operation depends on two factors: minimum flow and minimum water charge (minimum installation volume). The minimum flow is specified in the manufacturer's documentation.
The heat pump should therefore be provided with a minimum operating time at nominal power and less frequent start-ups, but this does not mean that it should operate around the clock without interruption. If the heat from the pump is not transferred to the heating system within this required minimum time, high-pressure disruptions will occur. The minimum required volume of water in the distribution pipes depends on the maximum heating power of the heat pump. If the volume of water in the heating circuit is not sufficient to ensure the minimum flow for the intended minimum operating time, central heating buffer tanks are used . Buffers limit the heat pump's on and off cycles.
The Roth Quadroline range of buffer tanks for heat pumps includes two types: a central heating buffer tank , the Roth Quadroline TQ-P buffer tank for series connection, and a central heating buffer tank with hydraulic clutch , the Roth Quadroline TQ-T buffer tank for parallel connection.
Check out the offer of tanks and containers at the Onninen wholesaler
Serial connection of buffer tanks (equivalent to Roth Quadroline TQ-P with two connections: heat source/heat pump supply and return) is on the one hand more beneficial (in terms of energy, due to the low temperature of the tank), but on the other hand it is hydraulically demanding - a bypass with a pressure differential relief valve must be built in to ensure minimum flow for the heat pump in a situation where one or more underfloor heating loops equipped with distributor valve actuators are closed. Systems of serial buffer tanks are recommended only in installations with one heating circuit and in a system with a maximum of one circulation pump , and they serve to increase the volume of the heating system.
In addition, we can distinguish supply and return buffer tanks . The advantage of including a buffer tank in the supply circuit is the possibility of integrating it with a heater as an additional heat source. The location of the tank in the return circuit is associated with a reduction in heat losses, but without the possibility of reheating the tank . Return buffer tanks are used to increase the volume of the installation and extend the operating time of the heat pump compressor.
Parallel connected buffer tanks (equivalent to Roth Quadroline TQ-T
with four connections: supply and return of the heat source/heat pump and supply and return from the installation, e.g. underfloor heating) separate the heat source (pump) from the heating circuit, thus fulfilling the function of a hydraulic clutch . Hydraulic decoupling is always necessary when connecting several heating circuits, including those operating at different flow values and with at least two circulation pumps (one pump from the heat pump supplies the storage tank and the other to the underfloor heating or underfloor heating and radiators). Such a connection is the safest way to avoid hydraulic errors. Parallel operation of the tank ensures the necessary minimum flow for the heat pump.
Buffer tanks ensure proper operation of the heat pump
- maintain the required minimum water flow through the heat pump condenser when the underfloor heating loops are equipped with distributor valve actuators that can limit the flow of heating water,
- guarantee the required minimum water supply for the correct operation of the heat pump unit,
- they act as a hydraulic clutch in an installation with an additional heat source , e.g. a gas boiler (connecting existing heat sources) or in a mixed installation of underfloor and radiator heating, operating at different flow values,
- store heat to perform the defrosting function of the periodically frosted evaporator of an air-to-water heat pump during the heating season at an outside temperature of ≤0° C (when heat is drawn from the environment in winter, the moisture condenses, freezes and restricts the flow; the heat pump starts defrosting to defrost the evaporator; the heat needed for this process is drawn from the buffer).
Roth Thermotank Quadroline for the preparation of domestic hot water
The characteristic feature of Roth Thermotank Quadroline domestic hot water tanks is their hygienic, "clean" way of operation. The domestic hot water is located exclusively in the 26 m long stainless steel coil for 325 and 500 l tanks and 38 m for the 850 l tank. The water in the coil for utility purposes is heated by the water in the rest of the tank (flow principle) and only in the amount that is needed, which eliminates water stagnation and the creation of an environment conducive to the development of microorganisms.
There are three variants of the Roth Thermotank Quadroline for DHW to choose from: the Roth TQ-TW 325/500/850 DHW tank with a coil, the Roth TQ-TWK kombi 500/850 DHW combi tank with a coil and a central heating buffer, and the Roth TQ-TWT kombi 500/850 DHW tank with a coil and a central heating buffer with a hydraulic clutch .
The capacity of the domestic hot water tank in combination with a heat pump should be selected depending on the demand for domestic hot water. The capacity of the domestic hot water tank does not depend on the power of the heat pump.
