Identification of Retrofit Options
After the identification of the inefficiencies, requirements and issues to be improved with the pre-retrofit survey and the energy auditing, different options appear as possible solutions with different investment costs and results. The identification of all the possible options is needed for the best choice of the suitable retrofit option according to the particular conditions.
The process for identifying the different retrofitting options has a special consideration in the cases with a stagged approach. The key of the staged upgrade approach is to complete improvements to building systems in the order that reflects the influence of one system on another.
Before addressing the replacement or re-dimensioning of the heating and cooling system as a retrofitting action, it is very important to analyse the influence of other retrofitting actuations over the heating and cooling loads and identify where the heating and cooling system can be resized to meet the demand of the optimized building.
Some measures directly reduce energy consumption such as replacement of inefficient lighting. The more efficient lights will emit less wasted energy into the building as heat, and therefore reduce the building’s cooling needs and potentially increase its heating needs. The envelope improvements may eliminate energy losses and reduce solar heat gain (through improvements in facade and windows) having a considerable impact on the building’s heating and cooling loads. By first completing retrofits to these systems, the next stage of retrofits can be optimized for the new heating and cooling demands. Figure below shows a simple workflow when analysing the retrofit options.
- 1 Building envelope
- 2 Lighting
- 3 HVAC
- 3.1 Ventilation
- 3.2 Renewables and heat pumps
- 3.3 Combined Heat and Power (CHP)
- 3.4 Storage and distribution
- 3.5 Cooling technologies
- 4 Intelligent Automation Unit
- 5 Operation and Maintenance
The purpose of this section is to summarize and categorize information regarding the building envelope for an easy consultation. Firstly, it starts with a review of the commercial insulating materials for walls, roofs and windows, including the innovative ones. The most promising solutions have been selected mainly on the basis of the optimal costs/performance ratio, taking into account also the pros and cons of each product.
The insulating panels with self-cleaning coatings to achieve both depolluting and self-cleaning effects in indoor environments have been included.
Insulating materials for walls/roofs
The most common materials for thermal insulation are:
- Mineral wool, a non-metallic inorganic product manufactured from glass (fiber glass) or rock (rock wool), which combines high thermal resistance with long-term stability, good fire resistance and acoustic properties;
- Expanded polystyrene (EPS) or extruded polystyrene (XPS), a polymer made from the monomer styrene, a liquid petrochemical. Polystyrene can be rigid or foamed;
- Polyurethane (PUR), where during an expansion process the air is exchanged with a lower thermal conductor gas, trapped in the closed pore system. It rises serious health concerns and hazards in case of fire, due to the release of hydrogen cyanide, which is very poisonous.
Their thermal conductivity is typically around 30-40 mW m-1K-1, decreasing to 20-30 mW m-1K-1 only in PUR. These values vary with temperature, moisture content and mass density.
The more innovative thermal building insulation materials are called “super-insulator”.
- Aerogel is a low-density solid-state material (0.2% of SiO2-chains) in which the liquid component of the gel has been replaced with gas (99.8% of air filled pores on a micro and nano size scales). Its thermal conductivity is 13-14 mW m-1K-1, but it can be decreased to 4 mW m-1K-1 using carbon black to suppress the radiative transfer.
- Vacuum insulated panels (VIP) consist of solid material with a high porosity level and a very small pore dimension on which a technical vacuum is produced and maintained by enveloping the solid core with a plastic and/or metallic sheets. The fine porosity of the matrix is very effective in decreasing the thermal conductivity and blocking the convective transfer, while making the core material of VIPs opaque (e.g. with a dispersion of carbon powder) reduces the radiative heat transfer. The application of VIP has important drawbacks: they cannot be cut for adjustment at the building site or perforated without losing a large part of their thermal insulation performance; moreover, the initial thermal conductivity increases from 3-4 mW m-1 K-1 to typically 8 mW m-1 K-1 after 25 years ageing, due to water vapor and air diffusion through the envelope and into the open pore structure of the core material.
- Gas-filled panel (GFP), which replaces air with a gas having a lower thermal conductivity, usually noble gases such as argon, krypton or xenon. GFP is made of two types of polymer films. Metalized films are used in a tied assembly called baffle, arranged in a three-dimensional form of multiple layers of cavities that produce a cellular structure which suppress convection and radiation. Low diffusion gas barrier foils are very thin layers of aluminum or polymer barrier resins that are used in a hermetic barrier, keeping the panels gas-tight. Thermal conductivities for prototype GFPs are quite high, e.g. 40 mW m-1 K-1, although much lower theoretical values have been calculated.
The document “Appendix 10. Insulation Materials SWOT Analysis” presents a SWOT analysis for the above mentioned materials.
The data of the insulation materials has been collected through a dedicated website, that is running at http://esdatabase.altervista.org/. On this website every user can create an account, with different privileges, that allows the user to complete a form with the required parameters for a material and create a new record in the database.
The choice of an insulation material can be made considering different parameters such as Thermal conductivity, Cost and Thickness. A higher thermal resistance can reduce the energy demand of the building, that is prescribed by the standards of the section. As construction have also strict budget limitations, the cost is a fundamental parameter. A reduced wall thickness may increase the value in the real estate, overcome legal or practical restrictions in the retrofitting of existing buildings, allow a reduction of transport costs.
The implementation of insulation solutions can be done through three different systems (external, internal and mixture), and each one is also subdivided in different categories. More information about the applicability of insulation solutions can be found in the document “Appendix 11. Applicability of insulation solution”.
Insulating products/technologies for windows
The manufacturers of windows are developing products more and more effective from the point of view of energy saving. The window is usually composed by one or more glass panes attached to a frame that covers typically less than 15% of the total area. In order to improve the insulation of the windows several strategies can be followed:
- Increasing the number of panes (triple-pane, quadruple-pane);
- Inserting gases with low thermal conductivity in the cavities between the panes (argon, krypton);
- Covering the internal surface of the panes with low-emissivity coatings in order to reduce the radiative heat transfer.
The frame is usually made of wood, aluminium or plastic materials (e.g. PVC) and could be designed with thermal break in order to lower the thermal transmittance.
In the current market, triple-pane windows with low-emissivity coatings and argon in the cavities between the panes are widespread, as required by several of the current standards. Their thermal transmittance can be lower than 1 W m-2 K-1.
The most insulated product available in current market is a quadruple-pane window with krypton in cavities between the panes, that guarantees a glass thermal transmittance equal to 0.3 W m-2 K-1 and a global thermal transmittance of the window equal to 0.6 W m-2 K-1.
For the windows products, as for the insulating products for walls and roofs, a database is available in http://esdatabase.altervista.org/page_wshowall.php.
Environmental issues become more and more relevant year by year, and topics related to the air quality improvement through air pollutants removal have created great interest in the research world. Photocatalytic methods are known to be widespread applicable in advanced oxidation processes (AOPs). Thanks to the high reactivity of the in situ generated active species, the selectivity of the photocatalyst is very low, leading therefore to the complete mineralisation of a wide number of organic pollutants (producing CO2 and H2O as final degradation products). Inorganic pollutants such as NOx and sulphureted compounds are converted into nitrates and sulphates respectively, while ozone is converted into O2. Photocatalytic processes are also active in removing microorganism: cellular membranes are degraded thus leading to the bacteria death . A large number of papers well resumes the main characteristics of a photocatalytic process . Titanium dioxide is considered as one of the most suitable photocatalysts because of its chemical stability, non-toxicity toward environmental and living species, low cost and wide availability . self-cleaning materials currently available include glass, concrete, ceramic tiles and paint . Photocatalytic paints can be conveniently applied in a wide variety of cases. Their use can help in preventing the diffusion of infections caused by antibiotic-resistant pathogens.
For the self-cleaning materials, as for the insulating products, the database is downloadable in http://esdatabase.altervista.org/page_home.php.
This section aims at analysing the main lighting systems along with their characteristics. The diagram below shows the main lamp types for general lighting:
Table 2 compares the main lamp types and gives the first indication of possible application fields. Note however that LED’s efficacy is sometimes quoted for lab conditions whilst in real conditions, this may be typically much lower due to thermal management aspects.
Several more specific comments on the main lamp types are given hereunder:
- There are two main types of CFLs: plug-in and pin-base. Pin-base CFLs are more common in non-domestic applications, they have a higher efficacy and are easier to dim.
- T5 fluorescent tubes are typically more energy efficient than T8, and are designed to be energy saving than T8 at higher ambient temperature.
- Different from the typical values identified in Table 2, Metal halide lamps can even reach up to 118 lm/W lamp efficacy in current product catalogues.
- Similar with Metal halide lamps, High pressure sodium lamps (standard) is reported that can reach up to 142 lm/W lamp efficacy, which is not described in the typical values in Table 2.
- LED’s efficacy depends largely on ambient temperature and its driver efficiency. Efficacy figures need to be checked rigorously. Not all LED lamps are dimmable, and some may flicker when dimmed. Colour rendering may also be an issue with some LED products due to their light spectrum.
It is reported that, among the aforementioned technologies, two thirds of the lamps sold were incandescent lamps. Incandescent lamps covered in 2004 about 37% of the light spots and they use about 25% of all the electricity used for lighting in EU-25 area. However, they produce only 4% of illuminance. With the legislation in Europe, incandescent lights have been banned since 2009. Hence the share of these light sources will decrease steadily.
With T8 lamps the trend is opposite, their share arrived at 13% of the sales, 34% of the light spots, 42% of the energy consumption, and they produce 58% of light. In commercial buildings and offices, the fluorescent lamp types are most commonly used. According to Table 3, electricity can be saved by replacing incandescent lamps with more energy efficient lamps. Other inefficient light sources are T12-lamps (3% of energy) and mercury lamps (4% of energy). T12-lamps and mercury lamps can be replaced with T8-lamps and high pressure sodium lamps, respectively. Metal halide lamps are even better replacement options for mercury lamps than high pressure sodium lamps. In lighting renovation T12 should be replaced with T5. Also new alternatives for the most energy consuming light source, T8-lamp, have to be found. According to Table 3, the average luminous efficacy of T8-lamps with ballast losses is 75 lm/W. At the moment T5-lamps with electronic ballast are more efficient. To date, LEDs are becoming the most efficient light source with the typical luminous efficacy of 20-120lm/W and exploitation potential of over 200 lm/W, however the power level is still one of the limiting factors.
Solid-state lighting is clearly the technology of the future and with the technological advances and the economies of scale of mass production this technology is predicted to revolutionize the market as shown in the graphs below from a study of Mc-Kinsey (Figure 3, Figure 4). Not only new installations but also retrofits will massively turn to solid-state lighting.
Natural illumination systems
Daylight is a free and sustainable source of light and the supply of daylight is typically at its highest during the hours with peak electrical energy loads. In function of the building type and layout, there may be enough daylight to meet the demand for lighting of a building during most of the working hours. Daylight is, however, also associated with negative factors such as glare and increased cooling loads. The challenge is to control daylight in a way that the light is utilized without glare, and the heat is kept out. Studies have shown that benefits of daylighting are not on only energy savings but also improved satisfaction, motivation of the occupants and productivity of the workers . Research has also suggested that daylight can help increase sales in retail spaces.
Advanced side lighting strategies can improve daylight penetration into the depth of the building by redirecting it onto a reflective ceiling: light shelves, sun-directing glass or anidolic collectors can be installed in the upper part of windows to redirect daylight deeper into the building; the electric lighting system needs to be controlled separately in the daylit and non-daylit areas to maximise energy savings while providing the required light levels.
Toplighting techniques, such as clerestories, northlights, sawtooth arrangements or rooflights, can use openings in the roof to allow daylight penetration into a space: hence their application is limited to single-storey buildings, or to the top floor of multi-storey buildings. However, daylight uniformity is significantly improved throughout the whole space, and there is less impact from obstructions, with maximum available daylight at all times. Because of higher and longer exposure to sunlight, irrespective of orientation, toplighting strategies – other than northlights – typically incur a higher risk of overheating than sidelighting. Atria and light wells can bring daylight into the building, whilst providing a focal point and aiding customer orientation within the space. Sophisticated arrangements of mirrors and lenses can be used to direct daylight (mainly direct sunlight) into specific internal areas of interest.
Another way to bring the daylight inside the building is via piping with reflecting surfaces. Companies like Solarspot, Monodraught ( Sunpipe ) and Wikoda ( Sunflower ) are offering such systems. Based on the latter manufacturer’s website, this seems to be a reflective technology rather than a piping one. Moreover, this is for small residential applications and it has limited use for commercial applications like this shopping centre. The piping usually has large diameters and the transmission efficiency limits the length of the light pipes to up to 10 meters or less, depending on diameter.
Another way is to have sunlight collectors outside of the building, distribute the sunlight via optical fibers to specially designed luminaires in the building. Fibre optic systems rely mainly on direct sunlight, as they are typically integrated within complex arrangements using sun-tracking collectors. This makes them less efficient for non clear sky conditions. Given their complexity, their price is typically much higher than that of other daylighting technologies. New daylight technology like Figure 5 and Figure 6 have been developed by The University of Taiwan.
This system, known as NLIS has an efficiency of around 5% for the moment, however sunlight is in the order of 10.000 lux and even a small fraction of this sunlight is already good enough to illuminate spaces inside buildings.
These systems are usually coupled with artificial lighting systems forming the so called Hybrid Lighting Systems. Efforts are ongoing on the three domains, i.e. daylight collection, transmission and distribution to constantly improve the efficiency and/or the cost. A sun-tracking pre-collector is being optimized and will be tested in the demonstration building on the premises of the National Taiwan University. Next to optical fibers out of PMMA, light pipes with collimating Fresnel lenses are being optimized as well as mirror array’s.
The Swedish company Parans, is also offering natural daylight systems of a similar concept. They are however concentrating the sunlight into one point which leads to high temperatures in the transmission system, requiring expensive glass based optical fibres.
Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis toward the aforementioned lighting technology have been carried out, detail information is available in the document “Appendix 12. Lighting and Daylighting SWOT Analysis”.
The purpose of this section is to categorize information regarding potential HVAC technologies to be applied in a retrofitting project. In this section the information will be summarized for an easy consultation, though this Guide, reader will find several linked documents for detailed information of each technology.
Mechanical ventilation system
Several mechanical ventilation systems are available for improving the air quality of shopping centers. The typical systems are recommended depending on the climates:
- Supply Ventilation Systems—Hot or Mixed Climates. Fresh air is drawn in through an air “intake” vent and distributed to many rooms by a fan and duct system.
- Exhaust Ventilation Systems—Cold Climates. Indoor air is continuously exhausted to the outdoors with one or more fans.
- Balanced Ventilation Systems—All Climates. With these systems, equal quantities of air are brought into and sent out of the shopping center. The two most common systems are “heat recovery” ventilation (commonly referred to as HRV) and “energy recovery” ventilation (commonly referred to as ERV).
Hybrid Ventilation System
Hybrid ventilation combines features of both mechanical and natural ventilation. The simplest often used definition of hybrid ventilation is “ventilation system that uses natural air intake through wall inlets in combination with mechanical extraction”. Although the mentioned ventilation systems certainly belong to the hybrid ventilation systems, the group of hybrid ventilation systems is considerably wider with the decisions quite different and strongly connected with the architectural design of the building.
The buildings with hybrid ventilation systems often are combined with other energy-efficient technologies such as passive and natural cooling, passive solar heating etc. as only integrated approach to the design of building and its mechanical system gives the best results in buildings energy optimization.
Renewables and heat pumps
Biomass combustion systems are the most widely recognized technology to convert a biomass feedstock into thermal (heat) energy. When burned, the chemical energy in biomass is released as heat. The heat is used to boil water in biomass boilers, creating steam. The steam can be used to serve a thermal load or to turn turbines and generators to produce electricity.
WIND ENERGY (MICRO WIND TURBINES)
Wind Power is converted to electricity by a wind turbine. Wind turbines come in a variety of sizes depending on the planned use for the electricity. Some wind turbines are used to charge batteries for buildings not connected to the utility grid.
SOLAR PHOTOVOLTAIC SYSTEMS
A photovoltaic system is an arrangement of components designed to supply usable electric power for a variety of purposes, using the sunlight as the power source.
PV systems may be built in various configurations: 1)Off-grid without battery (array-direct), 2) Off-grid with battery storage for DC-only appliances, 3) Off-grid with battery storage for AC and DC appliances, 4) Grid-tie without battery, and 5) Grid-tie with battery storage.
SOLAR WATER HEATING
Solar water heating (SWH) systems are designed to deliver hot water, different systems are available:
Direct and indirect systems:
- Direct or open loop systems circulate potable water through the collectors.
- Indirect or closed loop systems use a heat exchanger that separates the potable water from the fluid, known as the "heat-transfer fluid" (HTF), that circulates through the collector.
Passive and active systems
- Passive systems rely on heat-driven convection or heat pipes to circulate water or heating fluid in the system.
- Active systems use one or more pumps to circulate water and/or heating fluid in the system.
SWH is widely used in Australia, Austria, China, Cyprus, Greece, India, Israel, Japan and Turkey.
AIR SOURCE HEAT PUMP
Heat from the air is absorbed at low temperature into a fluid. This fluid then passes through a compressor where its temperature is increased, and transfers its higher temperature heat to the heating and hot water circuits of the building. There are two main types of air source heat pump system:
- An air-to-water system distributes heat via your wet central heating system. Heat pumps work much more efficiently at a lower temperature than a standard boiler system would. So they are more suitable for underfloor heating systems or larger radiators, which give out heat at lower temperatures over longer periods of time.
- An air-to-air system produces warm air which is circulated by fans to heat your home. They are unlikely to provide you with hot water as well.
GROUND SOURCE HEAT PUMP
Heat pumps provide winter heating by extracting heat from a source and transferring it into a building. Heat can be extracted from any source, no matter how cold, but a warmer source allows higher efficiency. A ground source heat pump uses the top layer of the earth's crust as a source of heat, thus taking advantage of its seasonally moderated temperature.
In the summer, the process can be reversed so the heat pump extracts heat from the building and transfers it to the ground. Transferring heat to a cooler space takes less energy, so the cooling efficiency of the heat pump gains benefits from the lower ground temperature.
WATER SOURCE HEAT PUMP
Water sources can be lakes, ponds, rivers, springs, wells or boreholes and the systems are usually classed as either ‘open’ where water is extracted from the source, flowed around the heat pumps intermediate heat exchanger (or an open loop rated internal heat exchanger) and then discharged; or ‘closed’ loop where, similar to a ground source, pipes or heat exchange panels are placed within the water source and a water/antifreeze mixture is passed through the pipes/panels absorbing energy from the water.
DC powered heat pump (DPHP)
A conventional heat pump system consists of compressor, condenser, evaporator, expansion valve, pumps and fans. On the other hand, a DPHP system has same components but the compressor and the fans are powered by DC energy source such as renewable or converted DC supply from grid line. Using DC powered HPs, which are more efficient than AC-powered HPs, can exploit renewable energy sources directly.
The renewable energy powered DPHP system is much more energy efficient than the classical heat pump system. Moreover, a longer lifelong period since these materials are used at exact cooling or heating demand (supply and demand is equal each other and there is no over capacity production) and also variable speed operation is applied instead of on-off operation. These operation modes extend the lifelong of the heat pumps' components.
Using renewable energy on a heat pump can be realized with AC or DC compressor, but AC compressor usage requires conversion from DC power to AC by using a power inverter. Inverter usage increases initial investment cost and also decreases energy conversion efficiency. Therefore, renewable energy powered heat pump, using DC compressor enhances efficiency and reduces initial investment cost due to the elimination of power conversion from DC to AC. Furthermore, the integration of variable speed compressor in the Heat Pump provides higher efficiency. In many studies, it is revealed that variable speed operation provides energy savings of 30%.
Combined Heat and Power (CHP)
Combined heat and power (CHP), also known as cogeneration, is the simultaneous production of electricity and heat from a single fuel source, such as: natural gas, biomass, biogas, coal, waste heat, or oil.
CHP is not a single technology, but an integrated energy system that can be modified depending upon the needs of the energy end user.
- Onsite generation of electrical and/or mechanical power.
- Waste-heat recovery for heating, cooling, dehumidification, or process applications.
- Seamless system integration for a variety of technologies, thermal applications, and fuel types into existing building infrastructure.
The two most common CHP system configurations are:
- Gas turbine or engine with heat recovery unit
- Steam boiler with steam turbine
There are also other CHP systems, such as Stirling Engine, Rankine Cycle Engine, Fuel Cell and Internal Combustion Engine.
CHP technology exists in a wide variety of energy-intensive facility types and sizes nationwide.
A number of site-specific factors will determine if CHP may be a good technical and economic fit for your facility. Answer a few simple questions to determine if your facility is a good candidate for CHP.
Storage and distribution
Thermal energy storage (TES) includes a number of different technologies. Thermal energy can be stored at temperatures from -40°C to more than 400°C as sensible heat, latent heat and chemical energy (i.e. thermo-chemical energy storage) using chemical reactions.
Sensible Thermal Energy Storage
The use of hot water tanks is a well known technology for thermal energy storage. Hot water tanks serve the purpose of energy saving in water heating systems based on solar energy and in co-generation (i.e. heat and power) energy supply systems. State-of the-art projects have shown that water tank storage is a cost-effective storage option and that its efficiency can be further improved by ensuring an optimal water stratification in the tank and highly effective thermal insulation. Today’s R&D activities focus, for example, on evacuated super-insulation with a thermal loss rate of λ = 0.01 W/mK at 90°C and 0.1 mbar and on optimized system integration. Hot water storage systems used as a buffer storage for domestic hot water (DHW) supply are usually in the range of 500 l to several m3. This technology is also used in solar thermal installations for DHW combined with building heating systems (Solar-Combi-Systems). Large hot water tanks are used for seasonal storage of solar thermal heat in combination with small district heating systems. These systems can have a volume up to several thousand cubic meters (m3). Charging temperatures are in the range of 80-90°C. The usable temperature difference can be enhanced by the use of heat pumps for discharging (down to temperatures around 10 °C).
Phase Change Materials for TES: Sensible heat storage is relatively inexpensive, but its drawbacks are its low energy density and its variable discharging temperature. These issues can be overcome by phase change materials (PCM)-based TES, which enables higher storage capacities and target oriented discharging temperatures. The change of phase could be either a solid/liquid or a solid/solid process. Melting processes involve energy densities on the order of 100 kWh/m3 (e.g. ice) compared to a typical 25 kWh/m3 for sensible heat storage options. Phase change materials can be used for both short-term (daily) and longterm (seasonal) energy storage, using a variety of techniques and materials.
Underground Thermal Energy Storage (UTES)
UTES is also a widely used storage technology, which makes use of the underground as a storage medium for both heat and cold storage. UTES technologies include borehole storage, aquifer storage, cavern storage and pit storage. Which of these technologies is selected strongly depends on the local geological conditions.
Borehole storage is based on vertical heat exchangers installed underground, which ensure the transfer of thermal energy to and from the ground layers (e.g. clay, sand, rock).
<u.>Aquifer storage</u> uses a natural underground water-permeable layer as a storage medium. The transfer of thermal energy is achieved by mass transfer (i.e. extracting/re-injecting water from/into the underground layer). Most applications deal with the storage of winter cold to be used for the cooling of large office buildings and industrial processes in the summer (Figure 9). A major prerequisite for this technology is the availability of suitable geological formations.
Cavern storage and pit storage are based on large underground water reservoirs created in the subsoil to serve as thermal energy storage systems. These storage options are technically feasible, but applications are limited because of the high investment costs.
Thermal Energy Storage via Chemical Reactions
High energy density (i.e. 300 kWh/m3) TES systems can be achieved using chemical reactions (e.g. thermo-chemical storage, TCS). Thermo-chemical reactions, such as adsorption (i.e. adhesion of a substance to the surface of another solid or liquid), can be used to store heat and cold, as well as to control humidity. Typical applications involve adsorption of water vapour to silica-gel or zeolites (i.e. micro-porous crystalline alumino-silicates). Of special importance for use in hot/humid climates or confined spaces with high humidity are open sorption systems based on lithium-chloride to cool water and on zeolites to control humidity.
Distribution: Radiant Ceiling Cooling
Low temperature heating/cooling systems are the most efficient and cost-effective way to reach and maintain ideal room temperature quickly and comfortably. In a low temperature system the distributing temperature of the water or air in the system is close to room temperature whereas in the traditional radiator distribution system, the temperature of the circulating water is (for heating) between 50 and 80°C. If the heat distribution is managed using a low temperature underfloor and wall heating/cooling system, the temperature of the water is only about 25 and 35°C. When the heat is distributed through the whole area, the temperature of the water can be much lower than that required in normal radiators. Besides, this heating system has a fast and accurate reaction to changing needs. Compared to convective heat emission, this system allows a more comfortable indoor climate at lower ambient air temperatures. In order to create the most pleasant indoor climate, the large heating surfaces require the lowest possible surface temperature. Also the homogeneity of the surface temperature contributes creating a high standard of comfort.
Buildings with radiant ceiling cooling systems, also known as “chilled beam” systems, incorporate pipes in the ceilings of the buildings through which cold water flows. The pipes lie close to the ceiling surfaces or in panels and cool the room via natural convection and radiative heat transfer. The technology has existed for more than 50 years; however, condensation caused moisture to accumulate on the cooled surfaces, causing ceiling materials (e.g., plaster) to fail and creating conditions favourable to biological growth.
A radiant ceiling cooling system directly delivers sensible cooling to spaces, de-coupling maximum air delivery from the cooling load and reducing ventilation fan energy consumption. Typically, the radiant and natural convection cooling capacity of chilled ceiling panels are comparable, with the combined radiant and natural convection cooling capacity being sufficient to meet peak sensible loads with approximately 50% of the ceiling area covered by cooled panels.
In typical commercial buildings, the strategy for avoiding condensation on radiant panels is straightforward. A separate system maintains the dew point in the space below the temperature of the radiant panels. In most instances, the predominant source of peak humidity load is the humidity contained in ventilation make-up air. Therefore, one option for handling the humidity loads separately from the chilled ceiling is to dehumidify the make-up air, with enough “extra” humidity removed to cover internal moisture generation, prior to introduction to the space.
These systems are the most versatile of the multi-split systems as the indoor units may function individually and will heat or cool individually. These systems are widely used in commercial buildings (shopping centers, offices, etc.).
VRV uses refrigerant as the cooling and heating medium, and allows one outdoor condensing unit to be connected to multiple indoor fan-coil units (FCUs), each individually controllable by its user, while modulating the amount of refrigerant being sent to each evaporator. By operating at varying speeds, VRF units work only at the needed rate allowing for substantial energy savings at partial-load conditions. Heat recovery VRF technology allows individual indoor units to heat or cool as required, while the compressor load benefits from the internal heat recovery. Energy savings of up to 55% are predicted over comparable unitary equipment.
An absorption chiller is a machine that produces chilled water by using the residual heat from sources such as steam, hot water or hot gas. Chilled water is produced by the principle of refrigeration that liquid (refrigerant), which evaporates at low temperature, absorbs heat from its surrounding environment while evaporating. Pure water is usually used as refrigerant, whereas lithium bromide (LiBr) solution is used as absorbent.
An evaporative cooler (also swamp cooler, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from typical air conditioning systems which use vapor-compression or absorption refrigeration cycles. Evaporative cooling works by employing water's large enthalpy of vaporization. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation), which can cool air using much less energy than refrigeration. In extremely dry climates, evaporative cooling of air has the added benefit of conditioning the air with more moisture for the comfort of building occupants.
Solid Desiccant Cooling System=
Desiccants are defined as materials which attract and hold water vapor. With desiccant systems the sensible and latent functions are separated. A desiccant material is used to remove the moisture by absorption or adsorption. Refrigeration is then used to lower the temperature only to the desired level for distribution. This refrigeration is done at a higher temperature than in a typical conventional HVAC thereby achieving a higher operating COP (lower kW/ton). A reduction in energy costs for air conditioning is possible.
Cooling towers are used to cool condenser water for rejection of chiller condenser heat. Cooling towers can be classified as open or closed. In open towers, the condenser water is contacted directly by cooling air. Most cooling towers for HVAC duty are open. In closed cooling towers, the condenser water flows in closed piping.
More information about Cooling and Heating technologies can be broke down into three categories: central, packaged and Individual AC, can be found in this document “Appendix 13. Categories of Cooling and Heating systems”. Also in the document “Appendix 14. HVAC and RES_SWOT Analysis”, a detailed SWOT analysis for different typologies of HVAC and Renewable Energy can be found.
Intelligent Automation Unit
The replacement or installation of insulation material, improvement in envelop, lighting system and HAVC systems can be effective in reducing energy consumption, as a holistic solution in retrofitting, besides the “Hardwar” upgrade, implementing Intelligent Automation Unit as the brain of the system could bring more benefit and further consumption reduction.
The information flow for the building control strategy is shown on the next figure. Data from Environmental processing unit and Acoustic processing unit are used to calibrate and build Building model. After that building manager can decide if he wants to run the building in manual mode (set the set points manually), or accept suggestions for optimal running of the building trough Optimizer unit.
On the next figure details of the Optimizer unit are shown. As it can be seen, the process of optimization starts with the Model Predictive Control (MPC) formulation. Since HVAC systems typically respond very slowly to the changes, one can use MPC to predict the behaviour of the system and apply the appropriate control inputs in advance.
One can choose between two main principle MPC formulations: deterministic and stochastic. This choice then determines the formulation of the constraints and cost function of the system. In Ecoshopping project the chosen MPC formulation is deterministic (sometimes also called Certainty Equivalence MPC). The advantage of deterministic MPC is in the fact that uncertainty takes expected value and in return this simplifies formation of the constraints. The main limitation is that if the weather prognosis in not as predicted precisely then the comfort bounds may be violated. This is most often dealt with by tightening the upper and lower bounds which in return provides the buffer zone for weather prognosis uncertainty.
There are two types of constraints that are to be enforced: room temperature comfort bounds (and any other like CO2 level or illuminance level bounds) and input energy limitations. For Ecoshopping project, the chosen constraint is comfort of people staying in the room (room temperature and relative humidity comfort bounds), because it meets the goals of the project (provide comfort for the occupants with minimum energy usage).
Soften the constraints
It is not always possible to satisfy all of the building constraints, so relaxation of the constraints needs to be made (softening constraints). The most logical way to implement this is that the least important constraint is first relaxed, and then the second least important constraint is relaxed next, and so on. This can be achieved by adding weighting matrices to each constraint. Cost function
Since the aim of the optimization is to minimize the energy consumption within the temperature comfort bounds it can be assumed that the cost of energy will reduce with lower energy consumption, so linear cost function is chosen. The linear cost function needs to be time depended in order to account for electricity prices that differ between day time and night time.
Once the constraints and cost function have been formulated, the resulting mathematical problem can be passed to the optimization algorithm. This algorithm will also need additional information in the form of constants and expected waveforms. More information on this is provided in the Inputs to the Optimizer section.
When the optimal solution is calculated, this solution is recommended to the control unit. As it has been seed before user can decide if this is an acceptable solution or the manual mode is more acceptable.
Introduction to the Optimizer
The behaviour of many dynamic systems can be represented by the following law:
- Equation here***************
where t is an instant in time, x is the state of the system, u is the input signal, and A and B are constants. This relation is basically saying that the next state of the system is the consequence of the input signal and state of the system in the previous state. In (1) constants A and B are derived from the dynamic model of an HVAC system. The main principle of MPC is to compute a control signal to minimize the objective function, which is a function of the system states. The system model above is then used as a constraint in the optimization problem. The MPC algorithm is set up to compute the optimal control signal over some period of time (number of steps in the future), but only the control signal at the first time step is applied before the optimization is re-solved and a new control signal is generated.
Optimizer working principle
The goal of the Optimizer is to suggest the most energy efficient way to pre-heat/pre-cool the building in order to reach the desired temperature for the morning opening hours of the building. Particular attention should be paid to consumption at the start of the occupied period in order to ensure the heating/cooling system is not coming on sooner than required. In general sense this is shown on the next figure. The blue line represents the normal heat-up period the starts at 4:00 but the building reaches temperature one hour earlier. On the other hand the green line represents the optimal start (delayed start) of the heating system at 5:00 hours in order to reach the desired temperature of the 22 °C at the 8:00 hours when the occupants start to arrive.
One thing to keep in mind is that during the night the price of electricity is usually lower than the price during the day. But on the other hand the room temperatures during the night are usually lower than during early morning so an optimum has to be found.
Optimizer works by assuming the default power profile that is needed in order to bring the building to desired temperature. This profile is then adjusted until the optimal solution is found. This is shown on the next figure. Time steps on this figure reprised the 15 minutes intervals so one step is equal to 15 minutes. If the Optimizer detects that there is no need to pre-heat/pre-cool the building it will simply take no action.
The Optimizer first tries to find solution by increasing the heating time and then if it cannot reach solution then it tries to increase the heating power. The time limitation is set at 7 hours. This means that the pre-heating operation cannot last longer than 7 hours. The power limitation will be set by the power output of the heating system.
In order to find the most energy efficient way to pre-heat/pre-cool the building the optimization process needs to rely on the good model of the heating/cooling system. When the Optimizer finds out how much heat energy needs to be added/removed from the building then this data can be forwarded to the heating/cooling system model. This heating/cooling system model then needs to determine what are the most energy efficient set points and forward this information to the control unit. Control unit will then set these set points for the heating/cooling system along with other HVAC set points. This can be seen on the next figure.
Inputs to the Optimizer
The main inputs to the Optimizer are current building temperatures and daily predicted thermal load. Building temperatures will come from the monitoring data server and thermal load will be predicted with the help of the Environmental processing unit and Weather prediction. Optimizer also uses the simplified building model in order to estimate how much heat energy needs to be added or removed from the building.
From the database parameters like Current Temperature, Wanted Temperature, Current Time and Date can be provided. Building opening hours is the parameter that needs to be provided by the building manager. Expected Thermal Load will be given by the Environmental processing unit and Weather prediction along with other parameters. In the next table full list of parameters is shown.
|Current Time and Date||Minutes|
|Building Opening Hours||Hour|
|Expected Thermal Load||W|
Table 4 Optimizer input parameters
Output from the Optimizer
In the first step output from the Optimizer is the heating/cooling power that needs to be added/removed from the building and for how long (system running time). With this information it is easy to determine the needed energy for this operation. In the second step outputs in the form of needed set points for the heating/cooling system are provided.
|Starting Time for H/C system||Minutes|
|H/C system set points||-|
Table 5 Optimizer output parameters
Operation and Maintenance
The aim of this section is to provide an Operation and Maintenance (O&M) plan for the equipment in commercial buildings.
O&M rating system: Key Performance Indicators
The Key Performance Indicators (KPIs) are used to show the level of achievements when addressing an objective and check the progress for this achievement. This aspect clears up problems that need to be solved and allows us seeing if the changes we make, or actions we take, actually help to resolve an issue.
The existence of a benchmark for the performance objectives that is set and the use of KPIs enables us to track the progress of critical factors and check the acceptability of equipment performance.
In a correct maintenance program, the operators have to deal with the removal of premature failures from equipment. For a good O&M work, two kinds of indicators will be used: Lagging and leading indicators. The O&M staff will use them to understand the equipment operation performance and identify the possible operational risks. More information is available in the “Appendix 15. O&M rating system: Key Performance Indicators”.
Operation and Maintenance manual
In this section, useful instructions for the maintenance program management are described focusing on the “data sheet” needed for O&M.
The required information for O&M should includes generic equipment information prepared by the supplier and project-specific information developed by the O&M designer. This document should contain information that describes either individual pieces of equipment that form part of a build-up system or individual packaged systems.
The use of standardized equipment data sheets is recommended as an effective method for collecting operation and maintenance information from the equipment suppliers in a form that is effective for the preparation of operation and maintenance programs.
The data sheet should be prepared for insertion in a binder. Alternatively, it may be prepared in the form of a data entry, possibly forming part of a computer-based maintenance management system. Such a maintenance management system should have the capability to link the necessary information from the equipment data sheet with additional information needs by the maintenance department.
More information is available in the document “Appendix 16. Operation and Maintenance manual”.
Operation and Maintenance plan
“Appendix 17. Operation & Maintenance plan” is a detailed document that includes the required minimum inspection and maintenance tasks related to 30 different equipment that can be installed in commercial buildings.
This check lists serve as the O&M procedures for HVAC, lighting anda daylighting technologies, sensor devices, insulation, which set a manual with instructions for the maintenance program management. The sheet structure and the required information are detailed. It is desirable to have an equipment data sheet prepared for each piece of equipment that will require operation or maintenance. Each equipment has a specific list with the “Inspection/Maintenance tasks” to be carried out and the frequency of these inspections.