8 actions to improve the energy efficiency of heating systems
Energy the efficiency of heating systems
In many buildings, HVAC is the first or second item in terms of energy costs. This technical article discusses tips for optimizing and saving energy efficiency in building heating systems.
8 actions to improve the energy efficiency of heating systems (heating system in commercial buildings)
Heating systems in the building
Heating systems have always been used when the outside temperature falls below a certain comfort threshold (a very relative concept in time and space). The majority of countries in Africa, South Asia, and Latin America do not use heating.
The choice of the type of heating and its energy source must be made from the outset when designing a building. It falls under the competence of specialists, architects, and engineers in heating.
In all cases, the search for savings involves the following actions //
1. Limit heat loss from the building
2. Prevent simultaneous use of heating and air conditioning
3. Avoid improper use of the heater
4. Optimizing the efficiency of heat generators
5. Use heat pumps
6. Using solar heating
7. Optimize heating circuits
8. Optimize heating control
1. Limit heat loss from the building
Depending on the level and variations of the outside temperature, heating, or air conditioning (air conditioning) systems keep the inside temperature at a comfortable level (typically 18 to 22 ° C). In constant operation, these systems add or remove the exact amount of heat needed to compensate for heat loss from the building (see Figure 1 below).
The first step is to minimize these losses. To do this, it is possible to //
· Design the exterior walls to limit the conduction and dissipation of heat by radiation,
· Insulate the roof,
· Use doors and windows with thermal insulation (double glazing, insulated doors),
· Treat cold bridges (door and window frames, load-bearing structures such as pillars or beams, etc.),
· Provide screens (shutters) to reduce losses through openings,
· Adapt solar shading devices to avoid solar radiation when cooling is required.
All these actions are facilitated when they are launched as part of the design of a new building and are therefore less expensive than in existing buildings subject to insulation and restoration constraints.
Cheaper solutions can, however, be applied to existing buildings, such as reducing the amount of outside air entering the building through opening doors and windows, or providing an entrance chamber. In all buildings, efficient heating management can also generate the savings described below.
2. Prevent simultaneous use of heating and air conditioning
The most efficient control systems can completely shut off part of the distribution circuit, be adjusted to prevent the simultaneous operation of heating and cooling systems, and have default settings suitable for the building.
For example, timers are an inexpensive technology for turning HVAC systems on and off at specific times, such as one hour before the start of the shift and one an hour before the end of the shift.
Done well, this has a negligible effect on occupant comfort as the thermal mass of the building maintains a similar air temperature for short periods. Holidays can also be scheduled, reducing the annual operating time. “Smart” time switches determine the optimum operating period, potentially further reducing the
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3. Avoid improper use of heating systems
Three tips to avoid improper use of heating systems //
Tip n ° 1 in all buildings housing commercial, industrial or administrative activities, a temperature should not be exceeded by 20 ° C to 22 ° C during heating periods. Temperature settings are necessarily higher in hospitals and health centers, while cooler room temperatures are possible in gymnasiums and sports halls.
Tip # 2 Prevent or limit the opening of windows (during cold episodes and heat waves) or make individual heating (and cooling) systems dependent on windows remaining closed.
Tip 3 Do not heat, or if necessary keep frozen, unoccupied, or partially occupied buildings just above (storage and service areas). For individual offices, premises, etc., it is possible to control the operation of the local heating or the opening of the air vents by a presence detector.
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4. Optimizing the efficiency of heat generators
Heating systems can be individual or centralized.
Individual systems generally use electric heaters (convector, radiant, or blower type) that heat each area ofthe building separately (offices, rooms, common areas). However, although the efficiency of an electric heater is 100% (all the energy used is converted into heat in the building), this type of heater is rarely the most economical.
To be effective, it must be controlled so as to turn off the heating when the room is not in use.
Centralized systems include a heat generator (boiler) and a distribution system. When heat is purchased from a supplier, energy is supplied through hot water pipes and thermal metering is used for billing purposes. In other cases, thermal energy is generated in a boiler located in the building. To be fully effective, a boiler must be of recent design, adjusted, and maintained by qualified personnel.
Its efficiency can be measured, regardless of the type of fuel, by monitoring the CO2 level and the temperature of the exhaust gases.
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5. Use heat pumps
Heat pumps can be used alone or in combination with a boiler, with the type used depending on the heat source.
The heat source can be the ambient air, but in this case, the pump cannot be used efficiently below a certain temperature, due to icing. “Air-to-water” or “air-to-air” heat pumps are therefore the most used in mid-season, with the boiler taking over during the coldest periods.
The heat source can also be groundwater, if available (see Figure 2 below), or the subsoil. The heat pumps are in this case of the “water-water” type and have a much wider range of use since they are not limited by the outside temperature.
Note // The efficiency of a heat pump is measured by its coefficient of performance (COP) , which is the ratio of the thermal energy supplied under specified temperature conditions to the electrical energy consumed by the compressor (and possibly the fan).
The COP of an “air-water” heat pump is 2 to 3.5 depending on the air temperature. A “water/water” heat pump can achieve a COP of 3 to 5.
6. Use solar heating
This solution presents two difficulties: it requires a good exposure (orientation) for the installation of the solar panels, and the availability of heat is by nature subject to weather variations. It can only be used as a complement to heating systems.
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7. Optimize the heating circuits
In the case of a centralized heating system when thermal energy is distributed to various buildings via water or air circuit, it is also advisable to save energy by reducing heat loss along pipes. This is essential for insulating water pipes or air ducts, especially in unheated areas (pipes, boiler rooms, service areas).
The power consumption of pumps or fans should also be reduced by installing variable speed drives in order to provide a level of propulsion that exactly matches the requirement.
8. Optimize heating control
The heating control system should ensure user comfort with minimum energy consumption as shown in figure 3 below.
In normal operation, all rooms which are actually used must be at a comfortable temperature. For periods when the buildings are not in use (nights, weekends, holidays), the temperature can be lowered by several degrees.
A minimum temperature just above the freezing point must be maintained at all times to avoid damage to buildings and their contents.
This optimization requires programming that must take into account //
The thermal inertia of the building. The heating must therefore be turned on a few hours before the occupants arrive and it can also be turned off before their departure. Fine-tuning these periods is very helpful, even with a temporary slight drop in comfort level.
The occupation of premises where it is possible to independently regulate the temperature of different parts of the building, thus avoiding the heating of unused or intermittently used rooms.
The outside climate (outside temperature, wind, sunlight) in order to estimate the heat loss of the building.
The “free contributions” provided by solar radiation, the metabolism of those present (about 75 W / person), as well as the heat generated by the processes (for example, cooking) and interior lighting. These free contributions are taken into account by the internal thermostats.
Finally, to improve user comfort, it is desirable to be able to individually adjust the temperature setting for each office. The adjustment is made using a thermostatic valve controlling a water radiator or a shutter controlling the airflow.
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