Solar heating technology (also known as solar thermal) converts solar energy into useful heat: economically, efficiently and safely. Now, with the rising cost of energy and fuel prices, the use of solar thermal energy is more relevant than ever. Already, Solar Thermal systems are found in every home, in their simplest form, that of the solar water heater, while Central Solar Thermal Systems are the usual choice for hotel facilities where the requirements for hot water are even tougher. However, solar thermal systems also have the ability to cover a significant part of the heating needs (heating assistance), which makes them essential for all new houses in the future.
The stringent targets for the Energy Performance of Buildings
Both the European and the National KENAK 2017 legislation for the construction of new buildings set strict conditions for their energy efficiency. Specifically, all newly constructed buildings, after 1/1/2022, must be necessarily classified at least in Energy Class A, i.e. their energy consumption must not be higher than 60 KWh/m2/year.
In the near future, newly constructed buildings in the European Union and Greece from 1/1/2025 and beyond will have to achieve primary energy consumption levels in the building's area of consideration as nZEB (Nearly Zero-Energy Buildings, with energy consumption < 25 KWh/sq.m./year).
While from 1/1/2030 and beyond, newly constructed buildings will be required to be zero energy buildings (ZEB).
In order to achieve such energy efficiency in the building, a combination of specific interventions is necessary, both in the building envelope (thermal insulation) and in the heating, cooling, ventilation and hot water production systems, with Solar Thermal Systems being an important piece in the "puzzle" of energy classification.
The house of the future: Upgrading the role of Solar Thermal
With the above energy requirements now a fact, climate change at its highest and the energy crisis overrun the entire planet, in the near future every home will be required, among other things, to have a Solar Thermal System, both for the production of domestic hot water and for heating.
Specifically, an installation in a new or energy-renovated house will usually include a hybrid system consisting of a Solar Thermal System, a Heat Pump and a Photovoltaic System, so that:
- The production of Domestic Hot Water be made exclusively by the Solar Thermal System.
- The Solar Thermal System can also contribute to Space Heating up to 50%.
- The Heat Pump covers the other heating and cooling needs at a rate of 50% to 100% (on days when there is no sunshine).
- The Photovoltaic System, to produce the required energy for the operation of the Heat Pump, the lighting and the other devices of the building.
In order to achieve the above performance in a 100 m2 residence, Energy Class A in Climate Zone B, is required:
- One Solar Thermal System with a solar tank of 500lt capacity and 8 m2 solar collectors surface.
- One Heat Pump 5KW (which consumes an average of 10KWh/day) and
- One Photovoltaic System 2.5KW with 12 m2 panels surface, in order to produce the energy consumed by the Heat Pump.
A system as in the example above, it 's a fact that will have a very good payback (ROI – Return of Investment), that it will save the money of its initial purchase in less than 5 years, in relation to the cost of energy saved in October 2022 prices. subsidized programs such as "Save", the payback time can be reduced to 2.5 years. With the subsidized programs such as "Saving at Home", the payback time can be reduced to 2.5 years.
The parts of the solar thermal system
A solar thermal system consists of the solar collectors, the solar tank, the solar station and solar controller, the piping, as well as accessories such as regulating valves, microfibers separators., three-way mixing and thermostatic valves.
Typical diagram of a solar thermal system for DHW production and assistance in heating.
The key role in the process of solar energy acquisition belongs to the solar collectors. They bind solar radiation (solar energy) and convert it into valuable heat (thermal energy). In place of the hose, the collector has an aluminum absorbent material. This binds the solar energy, heats and transfers the heat to the water passing through copper pipes, which rest on the absorbing. The special coating and the very efficient insulation ensure that as little solar heat as possible is lost.
Particular attention should be given to the efficiency of the solar collectors, as there are many low-efficiency collectors on the market that in the end reduce the overall efficiency of the solar thermal system. Ideally, the solar collector should have an efficiency of ηcol > 60%, so that with less surface area, it can achieve maximum efficiency.
Solar Tanks (boilers)
The solar tank collects the hot water which circulates in the solar collectors, storing the thermal energy. There are many types of solar tanks on the market. It is recommended that the solar tank be at least energy class C, and ideally it should be class B or A. Regarding the types of tanks, it is worth mentioning the following 2 types:
Temperature Stratified tank:
Thanks to their spherical exchanger, they stratify the water according to the different heat levels and therefore enable a particularly rapid use of the stored thermal energy.
These types of tanks are ideal for hotel facilities where frequent direct use of hot water is required.
Fresh water transit tank:
Η πιο συνηθισμένη επιλογή για νερό χρήσης και υποβοήθηση θέρμανσης. Είναι ιδανική επιλογή για χρήση σε συνδυασμό με αντλία θερμότητας, αλλά και λέβητες, κάθε μορφής. Διαθέτουν απλό σύστημα συσσωρευτή πολλαπλών λειτουργιών για νερό χρήσης και θέρμανση με ένα ηλιακό εναλλάκτη για φόρτωση ηλιακού κυκλώματος και ενσωματωμένο σύστημα υγιεινής προετοιμασίας ζεστού νερού σε διεργασία διέλευσης-θέρμανσης με ανοξείδωτο σπιράλ αγωγό.
The most common choice for domestic water and support heating. It is ideal for use in combination with a heat pump, and with any king of boilers. It has a simple multi-function accumulator system for domestic hot water and heating, with a heat exchanger for connection to the solar system. High water comfort and particularly hygienic is achieved with a stainless steel corrugated tube.
The solar station is responsible for the proper operation and synchronization of all the individual components. A solar station consists of the solar controller, the solar pump inverter, a safety valve, a manometer and thermometers, as well as non-return valves.
The solar controller is proposed to have remote control and configuration capabilities of the solar thermal system, via internet.
Pipes and Insulation for Solar Systems
For the proper circulation of the thermal fluid and the maximum reduction of the losses of the solar thermal system, the right pipe network is necessary. It is recommended to use spiral stainless steel pipe, certified for solar systems, as it requires particular resistance to temperature and pressure.
Components & Accessories for Solar Systems
Pressure regulating valves, microfibers separators, three-way mixing valves and thermostatic valves are essential components of a solar thermal system installation. They are required for hydronic balancing, regulation and ventilation of the solar circuit. It is recommended to use products certified for use in solar systems.
From the left: Thermostatic mixing valve, Regulating Valves, Solar Controllers
Most importantly: Dimensioning of the Solar Thermal System
In addition to the selection of the appropriate materials and products, as mentioned above, the most important factor in the installation of solar thermal systems is the proper dimensioning, which is the optimal design to create a single, economical, efficient and reliable heating system, which fully meets the needs of the building (in heating and domestic hot water production), but at the same time to reduce the annual operating costs of the system to such an extent that its amortization will be realized in the shortest possible time.
The responsible engineers must carefully record and study all the factors and needs of each installation and select the optimum design and materials for each case. This of course requires excellent expertise and knowledge of the products available on the market on the part of the engineers.
Finally, another important factor for the correct and efficient operation of Solar Thermal Systems is the regular maintenance, which must be carried out by qualified technicians.
Solar Thermal Technology - An important " tool" to address the energy crisis
All of the above leads us to the conclusion that in the face of a serious international energy crisis and with the daily explosion of energy costs, solar thermal technology remains not only one of the most timely and reliable solutions for increasing efficiency in residential, commercial and industrial heating and hot water production applications. It is the ultimate Renewable Energy Source, which, together with Heat Pump and Photovoltaic System technologies, will be the key component of all electromechanical installations for thermal energy production in the future.
The article by Georgios Char. Andrianos, as published in the industry magazine "The Plumber and the boiler installer - maintainer", November-December 2022.