Combined heating system - the choice and price of a mixed system

​Heat pump and gas/electric boiler​

First, before installing a heat pump, you must follow some rules:

• ​housing must meet the characteristics of an energy-efficient home. This implies insulation of walls, roofs, floors, as well as the presence of high-quality double-glazed windows;
• ​implementation of a ventilation system because without this system the load on electricity and heating system may be up to 25% per year;
• heating system with low-temperature mode:
  

1. there must be a system of underfloor heating, the area of which must be 100% of the entire floor surface, 
2. installation of fan coil units – universal devices that are capable of performing the function of cooling and heating.

To achieve efficient operation of the heat pump for heating and cooling the house, it is necessary to install additional devices: fan coil units, radiators, in-floor convectors as well as underfloor heating system (the area must be 100% of the entire floor surface).

There are several types of additional heat sources:

• ​fan coil units - the main task of the devices is to supply warm or cooled air, depending on the time of year;
• ​radiators - units that have only one function - heating;
• ​in-floor convectors - devices that can work on heating the house during the cold period of time. When using equipment from Kampmann HK, 

  you will also be able to cool the building in the summer.

Underfloor heating is a low-temperature and indispensable element of the heating system. At the same time, using only a system of underfloor heating is an irrational solution, since to maintain an optimal microclimate, the temperature of the floor surface will exceed + 24-26 °C, which will create discomfort for the human foot. Therefore, to achieve the maximum level of comfort, it is advisable to install additional equipment.

It should be noted that when implementing a heating system using underfloor heating, radiators and convectors, in the summer period you will not be able to perform the function of cooling the house. Therefore, by replacing radiators and convectors with floor-mounted fan coil units, you will get a comfortable air temperature in summer and winter.

​According to the method of placement, fan coil units are divided into several types:

• floor-mounted;
• ​wall-mounted;
• ​ducted;
• cassette.

Floor-standing fan coil units are considered the best option for installation in houses and apartments, since the installation of the device is carried out along the double-glazed window. This setting will help to avoid cold / heat gains in housing.

​In addition, Alter Air experts recommend installing a ducted air conditioning system, with which you can achieve the maximum level of comfort for a person, and it is also more suitable for this type of premises.

The heat pump is capable of performing not only cooling / heating functions, but also hot water supply, so you can use hot water all year round. In this case, it is necessary to consider the water flow rate, with which you can calculate the maximum amount of water consumption. Since the water limit must be calculated at the time of maximum water consumption, the correct solution would be to calculate the morning and evening time.

In addition, it should be noted that for country houses up to 200 m² it is recommended to use an air-to-water heat pump,  and for an area from 200m² - a ground source heat pump.  

A combined heating system with a heat pump and electric boiler means connecting the heat pump as the main source, and the electric boiler as an additional one. In the case when the air temperature is low outside and the heat pump cannot physically cope with the heating of the building, an electric boiler starts working. An important role in choosing a heat pump belongs to thermotechnical calculation. With the help of thermotechnical calculation, you can find out the range of operating temperatures up to which the air-to-water heat pump can independently cope with heating the house.

In this case, based on the data obtained, if the capacity of the heat pump is not enough, a decision will be made to additionally install an electric or gas boiler.  

In the case of choosing a gas boiler, Alter Air experts recommend using a condensing type gas boiler, as it is more efficient (COP (coefficient of performance) can tend to be higher than 100% due to the use of additional energy - condensate), in comparison with an atmospheric / turbocharged boiler.​

​Gas and solid fuel boiler

A combined heating system with a gas and solid fuel boiler involves the usage of a solid fuel boiler as the main element of the system, and a gas boiler as additional equipment. 

This combination is beneficial in the following cases:

• the design of the building does not meet the characteristics of an energy-efficient home;
• heating a house with your own raw materials, since buying fuel with a high density and a moisture content of no more than 30% is an expensive solution;
• limited supply of kW electricity to the house.

For the high-quality functioning of the heating system, it is necessary to follow some rules:

1. There must be a controller with which you can set the required temperature of the heat carrier, at which the solid fuel boiler will switch to gas.

For example, the residents of the house set the heat carrier temperature to +60 °C. As a result, when the temperature of the coolant is below the set one, the controller will provide an impulse to the gas boiler and the unit will start working up to the set temperature.

2. Transportation of hot water should be carried out by pumping groups, directly to radiators, floor convectors and underfloor heating.

Pumping groups are indispensable elements of the heating system, since they provide a higher temperature supply to radiators and convectors, and for underfloor heating (low temperature equipment) - a much lower temperature to prevent overheating of the floor surface.​

3. There must be a heat accumulator.

The process of burning wood is irreversible. Even without loading the solid fuel boiler with raw materials and stopping the air supply, the wood will continue to burn. Therefore, for a solid fuel boiler, it is necessary to install a buffer tank so that it can give the minimum amount of kW to a special barrel.

The calculation of the buffer capacity shows that for 1 kW, it is necessary to provide 40-45 liters of water.

4. There must be small and large heating circuits.

When the solid fuel boiler is turned on, the device should only work by itself up to a temperature of +60 °C. Thereafter, the boiler will be able to supply hot water for the heating system. If the temperature of the heat exchanger is below +60 °C, the condensation process will take place. As a result, the heat exchanger will become wet and eventually begin to deteriorate. To prevent this problem, a two-way valve must be installed.

The two-way valve is a device that controls the temperature of the solid fuel boiler, which must not fall below +60 °C. If this condition is not met, condensation will appear inside the device. In addition, condensation is accompanied by the release of a few kilojoules, since the heat will turn into steam, which will be thrown out into the street. As a conclusion, the solid fuel boiler will turn into low-efficiency equipment.

​In order for the combined heating system to be effective, it is necessary to have high-quality thermal insulation of the house and install a condensing type gas boiler.

When using a gas boiler of this type, it is necessary to use radiators that are designed for a heat carrier temperature of + 55 °C at the inlet to the device and + 45 °C at the outlet.

​Electric and solid fuel boiler

Combined heating with electric and solid fuel boilers in one system consists of using a solid fuel boiler as the main source of heat, and an electric boiler as an additional one.

The principle of operation of this mixed heating system in a private house is no different from a hybrid heating system of a solid fuel boiler and gas boiler.

At the same time, it should be noted that an electric boiler + solid fuel boiler, in comparison with solid fuel boiler + gas boiler, require more resources for the quality functioning of the system, since electricity has a higher price in relation to gas. Accordingly, combined heating with an electric boiler and a solid fuel boiler in one system is considered an irrational solution.

Gas, electricity, and solid fuels

The use of gas, electricity and solid fuels in one system are an impractical and costly solution. Accordingly, heating can be implemented in 3 options:

1. gas + solid fuel;
2. gas + electricity;
3. electricity + solid fuel.

Hybrid heating system with solar collectors

It is irrational to use a solar collector for heating a house because, due to low solar activity in winter, the device can not provide the house with the necessary amount of heat. Therefore, the solar collector is used only for hot water supply.