Solar Heating, Cooling And HVAC
Regulations across the country have required smarter cooling and heating in new buildings, and hence new buildings will become more energy efficient…
Solar thermal energy is appropriate for both heating and cooling. Key applications for solar technologies are those that require low temperature heat such as domestic water heating, space heating, pool heating, drying process and certain industrial processes.
Wall-mounted evacuated tube solar thermal system
Solar thermal systems consist of a solar collector, a heat exchanger, storage, a backup system and a load. This system may serve for both, space heating and tap water heating, known as combi system. Refer Figure 1.
Figure 1: Typical solar thermal system
In most applications, solar combi systems are used, generating energy for hot water and space heating, comprising mainly solar collector, heat exchanger and storage device.
One of the main advantages of solar cooling is the fact that cooling demand and highest solar gains are at the same time (summer period). Especially, in Mediterranean regions with high solar gains and high cooling demands solar cooling will become more and more an alternative to conventional cooling systems. For solar cooling in general two concepts are possible:
Cooling with PV collectors
A conventional vapour compression machine is operated by electricity provided by PV collectors. As the only difference to conventional cooling systems is solar produced electricity, as systems with thermal collectors are emerging and as systems with thermal collectors offer, promising approaches (both from energy efficiency and financial aspects).
This process employs a chemical refrigerant (e.g. R134a) and is the most common refrigeration process applied in air-conditioning.
Figure 2: Vapour compression chillers
Cooling with thermal collectors
There are three thermal driven systems:
• Absorption cooling with chilled water
• Adsorption cooling with chilled water
• Desiccant cooling for air based cooling systems
Main advantages of solar cooling are
• The availability of high solar radiation during the time when cooling is needed
• The applicability of thermal energy as driving energy
• Low operating costs
• Low electrical power rating
• Durability and environmental compatibility
The disadvantage of solar cooling systems is high installation costs, the space needed for heat storage and the additional backup system necessary.
Recommendations for solar heating and cooling
• Before considering active cooling systems the first step is to reduce the cooling load. This can be done very effectively by intelligent building design. Passive cooling strategies based on ‘bioclimatic design” (such as orientation and size of windows, reduction of solar gains by sunblind, implementation of thermal mass, night ventilation, etc). Due to this a simplified assessment of cooling loads in early design stages (e. g. architectural competitions) should be done. More detailed information can be found in the state-of-the-art report ‘Innovative cooling concepts for office buildings’.
• If solar heating and cooling is planned, solar collector areas need to be considered in early design stages, as they will have huge impact on the building design. This has to be taken into account by procurers, especially, for architectural design competitions.
• In climates with heating and cooling demand, combined systems (solar heating and cooling) make sense.
• Comparisons or assessment of the environmental impact of solar heating and cooling systems should be done on the primary energy level and on CO2- emissions. If possible technical specifications in tendering documents should deal with benchmark values of primary energy and CO2-emissions. It is recommended to use primary energy savings as a measure for the value of energy saving and using it during design and in the tendering process for comparison or assessment of different bids.
• As the calculation of costs (like payback times) in comparison to conventional heating and cooling systems is quite complex, expert input is required. Generally speaking costs (payback times) are effected by following aspects:
– Solar radiation on the site
– Efficiency of the HVAC system for heating and cooling
– Construction costs for the HVAC system for heating and cooling
– Additional construction costs for the implementation of the solar panels in the building structure
– Operation costs of the HVAC system
– Future development of interest on borrowings
– Future development of energy prices
Solar Air Cooler
Solar Air Conditioner
Heating Ventilation & Air Conditioning (HVAC)
The future of smart HVAC (heating, ventilation and air conditioning) systems is critical to the Indian economy with the cost of natural resources, especially, fossil fuels, undoubtedly set to rise over the coming years. Regulations across the country have required smarter cooling and heating in new buildings, and hence new buildings will become more energy efficient. But for the millions of homes and offices built over the past decades, smart HVAC systems will become a necessary investment if companies–and consumers–are determined to mitigate their effects on the environment and, of course, save money.
Heating, ventilation and air conditioning (HVAC) electricity consumption typically accounts for around 40% of total building consumption and 70% of base building (i.e. landlord) electricity consumption. It also contributes to manufacturing facility energy use and costs. HVAC dominates peak building electricity demand, so improving its efficiency can reduce peak demand electricity charges. Capital and maintenance costs of HVAC equipment also comprise a significant proportion of building costs. In addition, high performing buildings are now getting better returns as tenants and purchases are demanding to occupy sustainable buildings. The introduction of the Commercial Building Disclosure (CBD) regulations is also providing greater incentive for building owners to improve building performance and HVAC efficiency.
While significant energy and capital savings can be made through investing in energy efficient HVAC systems during construction of new buildings, good strategies exist to optimize energy use in existing HVAC systems. These strategies include reducing demand for HVAC services and ensuring good maintenance practices.
S D Bandal