Radiators in systems equipped with a buffer

A trend can be recently observed in heating to diversify the sources of heat in heating systems. Heating systems are often equipped with two or more heat sources, e.g. a gas boiler and a solid fuel boiler, a gas boiler and a fireplace, an electric boiler, a fireplace and solar panels. Users of such systems can manoeuvre the heat sources depending on changes in operating costs, fuel availability, season, heating requirements in relation to hot water needs, handling capabilities, etc. The problem in the use of such complex systems is their configuration.

Regardless of the heat source currently active, the system should achieve an optimum thermal effect. This task is complex since different heat sources pose different requirements to the system and its operation. Central heating boilers often are selected with excess in relation to average requirements. The outer design temperature for zone III in Poland is -20 degrees C, and the average daily temperature during the heating period is approx. 3-4 degrees C. this results in the work of the boiler below its optimal parameters, thereby causing its accelerated wear..

In the Polish climate with mild winters, quite sudden temperature changes, the use of systems with a buffer tank is particularly advisable. It provides a more economical and comfortable way of maintaining the desired temperature. The buffer tank is charged when there is surplus energy in the boiler/central heating system circuit, and discharged during increased demand for thermal energy. The time when heat is effectively generated is separated from the time when it is used. Heat is used in exact quantities at the time of actual demand. A buffer tank properly selected for the given building and its needs can be “charged” from any source of heat, operating at its optimal parameters. On the other hand, the heating system extracts heat from the buffer tank when there is demand for heat indoors, or for hot water

In a central heating system, the buffer tank stores heat and its task is to provide heat to individual heat emitters in the building. The buffer tank can be “charged” from a variety of sources and combinations thereof. For example:

– solid fuel central heating boiler

– solar panels

– fireplace

– clectric boiler (2nd tariff)

– heat pump (e.g. air-to-water)

The advantage of a buffer tank is that it takes heat regardless of the current demand of the building when it is the cheapest (from solar panels – during the day, from an electric boiler – during the 2nd tariff, from the heat pump – in temperatures above 0 deg. C) or under optimal operating parameters of the source (from a solid fuel boiler – at more favourable to the boiler and economical high performance, from a fireplace – when it is used). With heat stored in the buffer tank, you can use it when the demand for it arises in the building. Operating time between subsequent charges of the buffer tank depends on its thermal capacity and precision of collecting heat from it. The heat capacity of the buffer tank depends on its size and type of agent used. It should be matched to the capacity of heat sources and demand of the building for heat.

Selection of the buffer tank
Several conditions must be met for a system with a buffer tank to work with a maximum effect:

The location of the buffer tank can be determined based on common solutions, taking into account the impact of the location of the tank on the losses of the heat stored through the insulation. It volume can be determined from the formula:

where:

VSP – buffer tank volume [dm³]

TB – burning time [h]

QN – nominal boiler output [kW]

QH – heat load of the building [kW]

QMIN – minimum thermal power [kW]

For the average operating conditions and average size of the central heating system and the boiler, the volume of the buffer tank should be between 500 and 1500 dm³. The most simplified selection is defined by the formula: VSP = 40 QN

The buffer tank in a central heating system is a very convenient and versatile device, which could effectively cooperate with any heat source. The situation is different in regard to “discharging” the buffer tank. What’s essential is that the heat stored in the buffer tank lasts for as long as possible. Of great importance for the efficiency of the heating system with a buffer tank is the relationship between the volume (inertia) of the buffer tank, and the volume (inertia) of the system with radiators. System with a low volume of the heating medium, equipped with radiators operating in a high range of temperatures, is best suited for the needs of the central heating system as the emitter of heat received from the buffer tank. A low inertia system, correctly controlled, collects and doses heat very accurately. As a result, a single “charging” of the buffer tank is sufficient for a long period of operation.

When collecting heat from the buffer tank, the temperature of the heating medium goes down. Therefore, the system needs radiators which will effectively work under different parameters. This conditions is met by REGULUS®-system radiators, which are characterised by a very small own weight, water volume (inertia) and a very large heat dissipation area (effective work in a large supply temperature range).

In light of the above, the optimal solution is:

The radiator circuit with high total weight is much less economical in operation from radiators with a small weight. Experiments and calculations show that the optimal arrangement is as follows:

Regulus radiators, compared to a system of radiators with a high weight, achieve their full rated power much faster and at a lower cost of initial expenditure of energy. They start their efficient operation much faster. Similarly, when the buffer tank is discharged and the water temperature lowered, a big advantage of Regulus radiators is their very extensive heating surface. In addition, the materials – copper and aluminium – are very good heat conductors and cause the entire surface of the radiator is working intensively. Once the temperature desired by the user is achieved, radiators quickly cease heating – without undue inertia.

Surplus heat is stored in well-insulated buffer water tanks which heat domestic hot water and, if necessary, still precisely dose it for heating purposes. Therefore, it is very important that the heat loss from the tank is minimised and the heat lost remains within the building.

he more expanded the heating system is, the more visible are the positive economic effects of the use of Regulus radiators – radiators with a low total weight. For example:
A system consisting of 50 Regulus radiators – weight of the system = radiators – 350 kg, weight of water – 35 kg – total = 385 kg
A system consisting of 50 panel radiators with the same capacity – weight of the system = radiators – 2165 kg, weight of water – 345 kg – total = 2510 kg
A system consisting of 50 pipe radiators – old type – weight of the system = radiators – 3750 kg, weight of water – 1000 kg – total = 4750 kg

The vast difference of thermal inertia of individual systems greatly affects their efficiency – and operating costs. Precision providing thermal comfort and highly economical operation is a feature of a system of radiators with low weight..

A central heating buffer tank is a very good solution for heating systems both in new and modernised buildings. It has a number of advantages which, in consequence, increase comfort and significantly reduce operating costs.

REGULUS®-system radiators can be successfully installed in central heating systems equipped with a buffer tank. In such systems they show advantages as very good and efficient heat dispensers. They make it possible to maximise the use of accumulated heat in the buffer tank.