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Energy efficiency

These are thermal pump split systems. Every air-conditioning unit relocates energy in the form of heat from one place to another. Split means that the system consists of one body outside the building and one or more inside. The most popular are the wall air-conditioners offered in two types:

  • Conventional (working at constant compressor power);
  • Inverters (with automatic regulation of the compressor power);
Almost all air-conditioners are capable of working in heating and cooling mode. It is a small price difference between them and air-conditioner working in cooling mode only.
Thanks to the regulation of the compressor rotations, the consumable electric power of the inverter air-conditioners is decreased (up to 30 – 40 %). When the room temperature approximates to the intended, they switch to lower power mode operation. Thus they maintain the temperature in optimal limits – with no excess losses of power and at lower noise levels.
The heat power of the air-conditioner is given in BTU (British Thermal Units). 1 BTU is the quantity of heat needed for the temperature increase in one pound of water with one Fahrenheit degree.
To get an idea of the power of an air-conditioner, use the ratio 3.41 BTU = 1 W. Thus for example an air-conditioning of 9 000 BTU has 9000/3.41 = 2640 W power (typically the value is given for cooling mode).
The contemporary air-conditioners have relatively high power efficiency. Every 1 kW consumed electric energy they transform into approximately 4 kW heat energy.
There are two values which manufacturers characterize this efficiency with:
  • Coefficient of performance (COP) – in heating mode
  • Energy efficiency ratio (EER) – in cooling mode
In catalogues, these parameters have been reported under specific conditions:
  • COP is given at temperature + 7°С outside and + 20°С in the room;
  • EER is given at + 35 °С outside and + 27°С in the room, at 50% humidity. These conditions often differ from the real ones; therefore it is hard to create an overall preliminary image of the efficiency in practice.
At low winter (-5°С) or high summer (38- 40°С) temperature, the efficiency of the conventional air-conditioners strongly decreases as the lower classes of which even stop working. This problem is better solved in the inverter air-conditioners. They can work in heating mode at negative outside temperature down to – 20°С, something infeasible for a conventional air-conditioner.
It is important to know that:
  • An air-conditioner of insufficient power against the room volume, shall operate in non-economic mode despite of its good characteristics (COP and EER). Except that it shall be much more noisy and is likely to be damaged.
  • An inverter air-conditioner of higher power would be a better variant in view of power sparing.
  • In case the outlet supply air is of temperature lower than the body temperature (< 36.5°С), this air can be sensed as relatively cool and uncomfortable although the room will practically warm up.
  • In case of higher humidity in the premise, the air from the air-conditioner can be sensed as cool and uncomfortable although the room will practically warm up.
  • In winter, temperatures under minus 20 degrees, the air moisture on the external body shall form frosticles which strongly impair the heat exchange of it. Therefore it is necessary to remove it on a periodical basis. Most of the contemporary air-conditioners have autonomic defrosting mode.

Depending on the fuel, there are various solutions:

Wood and coal furnaces;
Processed oils boilers;
Gas wall boilers;
Pellet furnaces;
Electric boilers;
The ordinary solid fuel furnaces (cut woods or coal brickets) are hard and dirty to service, though quite cheap. The pyrolise boilers ensure better fuel consumption (ashes less than 4-5%) and are capable of continuous burning for 8-12 hours, i.e. they can operate with 1-2 charges a day. They achieve ECE up to 85%. They operate on the principle of dry wood distillation to the emission of generator gas which, mixed with a little air, is supplied for burning. To achieve maximal burning efficiency, the woods must be as less moist as possible (up to 20-30%), to avoid spending its calories for moisture evaporation. Minimal power supply is needed (approximately 40 W) to provide for the process of effective burning.

The boilers and pellet mantelpieces, the efficiency is very high, ECE is up to 94%.
They are comfortably serviced – automatic dosage, supply and burning of the fuel, with self-cleaning option and electronic process control and achievement of the desired temperature. The wooden pellets are pressed wooden waste of small size (diameter 6-10 mm and length 20-30 mm), therefore they allow automatic supply as opposed to the wooden brickets which are approximately ten times larger. They burn effectively, leaving very little ashes (less than 1-2%). They are poured into hoppers and directed to the burning chamber through an auger.
1 tone of pellets is sufficient for heating a volume of 75 m3 per season. To make pellets, fruit stones, wooden bark, wooden chips and other logging wastes are used.

To install and service the boilers being supplied with stored fuel, extra servicing room is needed of area of approximately 4m2 and height 2.50-2.60 m.

The thermal (heat) pump does not produce heat but it utilizes mechanical energy to relocate heat (where you want it – inside or outside the rooms). Thus it operates in two modes – heating or cooling. Тhe refrigerator and air-conditioner are thermal pump aggregates. The thermal pump construction consists of two heat exchangers, a compressor and a refrigerating agent.

The contemporary thermal pumps have high efficiency of conversion of electric energy (from 1 kW consumed electric energy, approximately 4 kW heat energy is sourced at external air temperature 7°С). The system is managed by temperature gauges and optimizes the electric energy cost.

This type of aggregates have supplement heat exchanger that utilizes the heat energy of the air sucked from the room:

In the winter – for heating the cold fresh air coming in the room;
In the summer – for cooling the incoming warm fresh air;
This energy in other cases is lost in atmosphere especially in cooling mode. Through the recuperator, significant energy saving is achieved.
Most of the recuperators utilize the heat from the work of the compressor itself – to supply domestic warm water.

The vapour resistance of a material is a measure of the material’s reluctance to let water vapour pass through. The vapour resistance takes into account the material’s thickness, so can only be quoted for a particular thickness of material. It is usually measured in MNs/g (“MegaNewton seconds per gram”). If the quantity is measured in MNs/gm (notice the small “m” at the end) then it’s actually a vapour resistivity and should be dealt with as explained on the next page. The µ-value (“mu-value”) of a material is also known as its “water vapour resistance factor”. It is a measure of the material’s relative reluctance to let water vapour pass through, and is measured in comparison to the properties of air. The µ-value is a property of the bulk material and needs to be multiplied by the material’s thickness when used in a particular construction. Because the µ-value is a relative quantity, it is just expressed as a number (it has no units). You might see the reluctance of a material to let water vapour pass through expressed as an “equivalent air layer thickness”, which is usually represented as sd. As its name suggests, the equivalent air layer thickness is measured in metres. Like vapour resistance, it can only be quoted for a particular thickness of a material.
You might also see the vapour resistivity of a material quoted. This is similar to the vapour resistance, but is a property of the bulk material and is usually measured in MNs/gm (“MegaNewton seconds per gram-metre”).
An associated unit is the “perm”. This is a measure of permeance, or water vapour transmission. Like vapour resistance, it is a measure associated with a given thickness of material.

Ventilation is a process of air exchange in a building for ensuring of fresh air for the inhabitants. Except for the improvement of the heat insulation, the planning of the building should not neglect the quality of the air in it as well.

There is a variety of reasons that necessitates the ventilation:
The evacuation of the collected carbon dioxide which is harmful;
Тhe reduction of the humidity in the rooms resulting to condense and mould formation;
To provide for fresh air, nothing used to be done in the near past since the joinery works were not well sealed and let through enough air. The utilization of the new PVC and aluminum joinery works “tight” the houses and the air became unhealthy for breathing. Condense moisture and mould appeared in the homes.

To achieve optimal micro-climate in the rooms, it is necessary to ensure more than 25-30m3/h fresh air for a person at relative humidity of 50%-60%. Ventilation is necessary in the mornings for every room for approximately 20-30 minutes, 3-4 more times during the day as well as after cooking, bathing or drying laundry.

The typical ways of room ventilation are:
Through manual opening of windows and doors;
The opening of windows and doors is the most accessible and cheap way of ventilation. But if done frequently, it results in large energy losses. We lose air of optimal temperature and we import air that needs to be warmed or cooled from that moment on. The heat comfort in the room is impaired. Also, we can hardly estimate the ventilation duration.

Through ventilation system with recuperator;
Overall ventilation system (with recuperator) prevents the compromises of the manual ventilation, achieving energy saving. The larger initial investment is a disadvantage.

Through ventilation system with inlet valves;
Ventilation with inlet valves is an intermediate solution option in case of insufficient budget. The heat losses are significantly reduced as opposed to the typical ventilation.

Through micro-ventilation in the window wing;
Ventilation through the upper part of the window (micro-ventilation) is also a solution, but very few companies offer it as an option.

The ventilation through inlet valves is an intermediate solution option for self-regulating ventilation in case of insufficient budget for ventilation system with recuperator.

Self-regulation depends on the humidity level in the rooms. Special humidity sensitive tape reacts to the humidity in the rooms and changes its length. As a consequence of this, the valve is mechanically opened and lets in fresh external air in the rooms.

The inlet valves are assembled on the external walls or windows. They are moisture sensitive and dose the fresh external air flow to the rooms. One inlet valve is sufficient for an area of 20 m2. On the internal wall of each room is mounted exhaust valve, through which the stuffy and wet air is evacuated to the air ducts. Exhaust fans provide forced air circulation, thus removing air exhaust. To provide unimpeded circulation, all internal doors must have certain distance to the floor or small opening in the lower end.

The micro-ventilation is the easiest way of self-regulating ventilation *. The airing through micro-ventilation relies solely upon ensuring that the air passes through the windows without forced air circulation in the rooms. Self-regulation depends on the power of the external air flow. Special plate mounted in the sash of the window closes automatically when the pressure of the outside air flow exceeds certain level.

* Ventilation of automatic operation mode without the involvement of the inhabitants.

The thermal inertness determines the heat-accumulating capability of materials. It indicates their resistance to temperature changes. The materials of high heat inertness can accumulate and radiate significant quantity of heat energy. In change of the ambient temperature they relatively slowly change theirs, slowing down the change of the temperature in the room they are placed. Briefly said, the massive walls are slowly heated and slowly radiate heat.

It is important to know that:
The materials of big heat inertness are heated quite slower;
The reduction of the material density results in the reduction of the heat inertness. For example a  wall, constructed of hollow bricks has smaller heat inertness than wall constructed of thick bricks;
Using of gypsum board instead of gypsum fine plaster in the rooms reduces the thermal inertness;

Thermal (cold) bridge is an element of the building, through which the quantity of heat that passed is bigger than through the other part. It is also called a cold bridge.

These are all parts of the building where heat is lost as a result of temperature difference between the external and internal environment. The interruption of the thermal bridges is a separation of the heat transfer between building structure elements and the outside environment. This is done by placing the external heat insulation.

Съществуват ветрогенератори с вертикална и хоризонтална ос на въртене. И двата вида изискват стартова скорост на вятъра около 2-3м/сек и работна скорост около 25м/сек. Турбините се монтират на мачти (с обтяжки), които имат височина минимум от 6м (около 12-15м при средните модели). При турбините с хоризонтална ос, система за следене посоката на вятъра завърта роторните витла срещу въздушния поток. Ветрогенераторите с вертикална ос са независими от посоката на вятъра. Те имат и по-ниска стартова скорост в сравнение с конвенционалните, безшумни са, без вибрации на мачтата. Затова са приложими дори и в градски или извънградски фамилни къщи. Инвестицията в среден модел (с мощност 5-10kW) ветрогенератор струва около 9 000-18 000 евро.
Вятърната енергетика все още изглежда непривлекателна за инвестиране в широки мащаби. Законът за енергията от възобновяеми източници (ЗЕВИ) не дава ясна и стабилна рамка за развитието на проектите. Вятърните централи изискват огромни инвестиции в проучване и измерване на вятърен ресурс, проектиране, осигуряване на подходящо оборудване и строителство, а няма яснота дали проектът ще възвърне направената инвестиция. От друга страна, ако не бъдат направени необходимите проучвания, съществува реална възможност вятърната централа да бъде неефективна. Освен това, преобладаващите ветроскрости на територията на България са ниски (до средни) и затова конвенционалните вятърни турбини не са ефективни.
Най-големите ветропаркове са концентрирани в Североизточна България, където ветроскоростите са по-високи, но съществуващата електропреносна мрежа е с малък капацитет, недоразвита поради традиционно селскостопанския характер на района. Нужно е разполагането на високоволтажна инфраструктура в недоразвитите региони. Силата на вятъра около бреговете все още е твърде недостатъчно използвана за производство на енергия.
Обикновено вятърните централи работят най-ефективно между 4 и 6 часа сутринта, когато потреблението на енергия е ниско. Така, заради непостоянната си работа, те не могат да участват в баланса на енергийни мощности за територията на България (често дори се оказват рискови за системата).

The decrease of the non-renewable resources gradually increases the price of their utilization. Since the building fund has the largest share of the energy consumption, objective indicators have been created giving clear view of how much energy certain building consumes. Along with the calculation for the heating, the cooling parameters are monitored as well.

As a major indicator of building energy efficiency, the total annual energy consumption for heating, cooling, lighting, hot water and appliances is considered.

The annual energy consumption is characterized through two parameters: consumed energy and primary energy.
Consumed energy is the annual quantity of energy supplied or that must be supplied to the building;
Primary energy is determined by increasing the consumed energy with the relevant losses for yield (production) and transfer;
The specific energy consumption is determined as the total annual energy spending (kWh) is related to the building area (m2). Annual unit of measure kWh/m2 is thus obtained. Depending on this value, each building falls in the relevant class for energy efficiency (see chart). Based on this, energy passport is issued, reflecting the building energy features.

Renewable energy sources are all sources that practically cannot be exhausted when utilized by people for energy sourcing.

Known RES so far are:
(energy from solar and photovoltaic panels);

(energy from wind generators);

(energy from WES, tidal, sea waves);

(energy from geothermal installations);

(energy from biomass stations);

Generally, the production of energy from recoverable sources is supported by the European legislation. When you use recoverable energy source, you can rely to buy the electric energy at preferential prices.

Regrettably, the utilization of energy from non-renewable sources is still prevailing:
Natural gas;
Nuclear (uranium) power;

The standard “Passive house” achieves reduction of the energy consumption with 80-90%.

Main requirements, mandatory for the standard are:
Annual energy consumption for heating/cooling ≤ 15 kWh/m2, for a year;
Annual energy consumption for all energy needs of the building ≤ 120 kWh/m2, for a year;
Air impermeability of the building ≤ 0.6 ACH @ 50 Pascal tension, measures at Blower-door test.
Further requirements depending on the climate:
Windows with total coefficient U ≤ 0.8 W/m2K;
Construction without thermo bridges ≤ 0.01 W/m.K;
Ventilation system through utilization of the energy of the evacuated air at efficiency above 75% and low electric consumption below 0.45 Wh/m3;
The windows of the passive house are triple glass package and favorable exposure. This is almost air-tight building which has ventilation system with recuperator for energy saving utilization, with controlled fresh air supply. Overheating of the rooms is avoided through suitable measures for sun protection.

PHPP (Passive House Planning Package) is a calculation methodic especially created for the design of passive buildings.

The coefficient of heat conductivity expresses the quantity of heat passing through certain material – for area of 1m2, per 1 second, through 1m thickness, at 1 degree difference between the two sides of the material concerned. It is measured in W/m.K

The thermal conductivity is determined for homogeneous materials. The less the value of λ is, the better the heat insulation properties of the relevant materials are.

As a comparison, here are the values of λ for some materials:
Reinforced concrete, λ= 1,6 W/m.K;
Masonry of hollow bricks, λ= 0,52 W/m.K;
Steel, λ= 53,5 W/m.K;
Gypsum board, λ= 0,21 W/m.K;
Gypsum fiberboard , λ= 0,30 W/m.K;
Hydrophobic plywood, λ= 0,15 W/m.K;
Mineral (rock) wool, λ= 0,035-0,045 W/m.K;
OSB, λ= 0,13-0,15 W/m.K;
EPS (expanded polystyrene), λ= 0,035-0,042 W/m.K;
XPS (extruded polystyrene foam), λ= 0,028-0,034 W/m.K;
(for more information about often used building materials – see Dictionary)

The coefficient of thermal transfer U-value considers the quantity of heat transferred through the surrounding elements – for area of 1m2, for 1 hour, at 1 degree difference between the temperatures on the two sides of the element concerned. It is measured in W/m².K

It is calculated by considering separately the thicknesses and coefficients of heat conductivity of all materials these elements are made of. The less the value of U, the better the heat insulation properties of the relevant element.

The U-value is not an abstract notion but it gives a clear image of the quantity of our energy waste.

Water vapour resistance factor µ determines the material’s reluctance to let water vapour pass through. High µ-value means high resistance to water vapour transmission. More and more attention is paid to this important feature, because of the frequent problems with condensation and mold in the buildings.

µ-values for some materials:
Reinforced concrete, µ=90;
Autoclaved aerated concrete, µ=6;
Masonry of thick bricks, µ=7;
Steel (plate), µ=600 000;
Window glass, µ=10 000;
Gypsum board, µ=12;
Gypsum fibre board, µ=10-15;
Wooden fiber plates, µ=10;
Hydrophobic plywood, µ=60-100;
Mineral wool, µ=1; (best value) !
OSB/3 (Oriented Strand Board), µ=250;
EPS (expanded polystyrene), µ=40;
XPS (extruded polystyrene foam), µ=170-200;
(for more information about often used building materials – see Dictionary)

Mu-value is a relative and can orient us which of the materials is less water vapor permeable in principle. So in practice we use another indicator Sd-value [m]. It indicates the thickness of a static layer of air that has the same water vapour resistance as the building material of thickness t [m] Sd = μ. t
Measured in meters [m].

Sd ≤ 0.5 m (diffusion-open)
Sd > 0.5 m (diffusion-blocking)
Sd ≥ 1500 m (diffusion-proof)

The geothermal installations draw heat from the earth in winter and evacuate heat from the building back to the earth in summer. They utilize the relatively constant soil or underground water temperature as a heat source. The underground layer at depth of more than 3 m is with temperature of approximately 7-14° С throughout the year. At bigger depth, temperature variations are even less (see diagram).

According to the heat drawing, the following geothermal installations are differentiated:
Open system (through direct water pumping);
Closed system (through circulation of antifreeze or refrigerating agent);
According to the digging works, the following geothermal installationsare differentiated:
With vertical drilling (for rocky earth or lack of area);
With coil in a wide shallow excavation (for softer soil and sufficient yard area);
The drilling solutions utilize two ways of used water evacuation:
By one drill and drainage in the canalization (for sufficient quantity of underground waters);
By two drills and drainage back to the earth (to prevent from unbalancing the level of underground waters);
Practically, drilling at the depth of less than 15m is of little efficiency and is financially unreasonable.

The sun is the biggest energy source to the Earth. Every second, the Earth atmosphere is reached by 1,35 kW/m2 energy as only for a week, the sun gives us more than we can obtain from all available energy reserves on the planet.

Though similar in appearance, there is a significant difference between the solar and photovoltaic (PV) panels.
Solar panels (sun collectors) are directly heated by the sun and the system produces warm water (see chart).
Photovoltaic panels generate electricity (direct current) from the sun light. The electricity from them can be kept in special batteries or be directly consumed or can be sold to the local electricity company.
Solar thermal system
Solar thermal system (for domestic hot water) consists of four components:
Thermal collector (solar panels)
Reservoir tank (for storing hot water)
Solar station (connects thermal collector and reservoir tank)
Solar regulator (automatic control panel)
The ideal location of the solar panels is what ensures maximally good heating. It depends on the seasons, geographical exposure and panel slope. In winter, the solar panels strongly decrease their efficiency.

Photovoltaic system
Photovoltaic system (for generating electricity from the sun) consists of three components:
Photovoltaic (PV) module
Inverter (converts DC power from PV modules into AC power)
Second electricity meter (energy income account)
The ideal location of the photovoltaic panels is that one they receive most light. The south exposure is desired but far from obligatory. The most effective are the small slopes (approximately 30⁰). Typically, good ventilation of the space behind the panels is needed. The system works even better at low temperatures, i.e. in winter, provided that the weather is clear and it is not covered with snow. The effectiveness is strongly decreased in shadow, fog or clouds.

The power of the photovoltaic system is typically stated as nominal, measured in kWp or Wp (”p” – peak) – at 1000W of radiation power for 1m2, at 25°С cell temperature and 1.5 times the sun radiation penetration degree in the environment.
The quality offers on the market are with provided protection from hail (armoured glass). The thunderbolt protection obligatory for every roof prevents from thunderbolts falling. Except photovoltaic (polycrystalline and monocrystalline) modules, the system is equipped with regulator, inverter, batteries, etc.).
For facilitation, the practice considers that every 1000 W power of the system needs approximately 10 m2 area.

There are wind generators of vertical and horizontal rotation axis. Both types require start wind speed of approximately 2-3m/sec and work sped of approximately 25m/sec. The turbines are assembled on masts (with tensioners), which are of minimum height of 6m (approximately 12-15m at the average models). In the horizontal axis turbines, the wind direction monitoring system rotates the rotor propellers against the air flow. The wind generators with vertical axis are independent from the wind direction. They also have lower start speed compared to the conventional, noise-they are free, mast vibration free. Therefore they are applicable even in urban or non-urban family houses.

The wind stations require huge investments in the investigation and measuring the wind resource, design, provision of suitable equipment and building. If the necessary research is not carried out, there is a real likeliness that the wind station is ineffective.

The biomass is a organic material that can be used (directly or after transformation) for the production of energy. The main groups of biomass sources are:

Perennial “energy” plants;
Fast growing trees of solid wood;
Agricultural cultures and vegetable oils;
Weeds and sea micro-flora;
Household and industrial limited wastes;
The wastes pollute the environment – they can be a source of biogas instead, through fermentation processes. A significant quantity of biomass is created when growing farmer cultures and cattle (manures, sediments). The decay of these wastes releases methane that is much more hazardous to the environment than the carbon dioxide therefore the methane should be assimilated and utilized as biogas.

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