HVAC Configurations Research Articles

Assessment of different HVAC configurations in a Conference Room with thermal stratification for improved microclimate conditions

Assessment of different HVAC configurations in a Conference Room with thermal stratification for improved microclimate conditions

Daily, monthly and seasonal energy performances and economic assessment on the coupling of an earth to air heat exchanger to an already existing HVAC system: A case study for Italian cities

The main aim of the investigation introduced in this paper is to analyze and identify the energy saving and the economic return deriving from the investment of placing an Earth to Air Heat eXchanger (EAHX) as pretreatment unit of a HVAC system serving buildings of a company operating in the industrial sector in Italy. This hybrid system is aimed to take advantage of the heat capacity of the soil surrounding some buried pipes for passively preheating and/or precooling the air before it is ventilated into the building. The buried pipes can then provide preheated and/or precooled air to improve the energy performance of the HVAC system, and ultimately to ensure indoor thermal comfort conditions.The company has various offices in Italy and so a the hourly, daily, monthly, yearly performances of the EAHX, the energy saving of the hypnotized solution with respect to the base HVAC configuration, as well as the economic impact of the investment in terms of payback time and net present value have been investigated and a comparison among different climatic zones of Italy is reported. To perform the above-mentioned objectives a two-dimensional numerical model of a dominium including the soil, the surface and the buried tubes of the EAHX is introduced. The model, experimentally validated and solved through the Finite Element Method, is forced with dynamic boundary conditions on the intensity of the solar radiation and on temperature and relative humidity of the external air entering the tubes, for many Italian localities.The employment of the EAHX in the HVAC reduces the energy consumptions in the various considered Italian climatic zones from: −30 % to −45 % in heating mode; from −23 % up to −43 % in cooling mode. From an economic point of view, the investment at the end of lifetime (25 years) is always positive and it has a discrete return in all the cases investigated.

Energy efficiency in hospitals: comparative analysis of different HVAC configurations

ABSTRACT The characteristics of health facilities e.g. the need to operate 24 h a day, strict cleaning procedures and indoor environmental parameters made these building-type energy-intensive. The huge potential that can be exploited in terms of energy savings is evident, mainly regarding the HVAC system refurbishment. From literature emerges that there are poor systematic analyses concerning all the possible HVAC retrofit scenarios, considering solutions currently on the market or renewable sources. To fill the research gap pointed out, the present paper proposes a rigorous analysis of the possible generation subsystems available on the market that can be implemented in an HVAC retrofit for a hospital. A real case study of 88,000 m3, represented by a hospital in southern Italy, has been used. Different technologies, such as the photovoltaic system, electric heat pump, absorption heat pump driven by solar energy, cogeneration are analysed from the energy and environmental point of view, with the introduction of the Imported Energy Level Index (IELI). The best retrofit measures is the installation of an absorption heat pump driven by solar thermal collectors and cogeneration, with a primary energy saving of 20%. Considering the installation of a heat recovery unit, the saving is up to 43%.

Evaluation of the Impact of Input-Data Resolution on Building-Energy Simulation Accuracy and Computational Load—A Case Study of a Low-Rise Office Building

Building-energy consumption is the primary aim of urban energy consumption, which can aid in optimization of building operation and management techniques, creating sustainable building and built environments. However, modellers’ understanding of the relationship between building-energy modelling (BEM) accuracy and computational load is still qualitative and deprived of accurate quantitative study. Based on a bottom-up engineering methodology, this study aims to quantitatively explore the effects of building-model input data with different resolution accuracies on energy simulation results, including evaluation of computational load. According to the actual parameters of the case-study building, 108 models with varying input resolution levels were developed to estimate hourly energy usage and annual mean ambient temperature. The results demonstrated that with input parameters at low resolution levels, geometric parameters such as exterior windows, interior windows, and shading exhibited significantly lower computational loads, resulting in reduced errors in the final simulation performance, whereas the occupancy schedule, thermal zoning, and HVAC configuration parameters exhibited significant declines in simulation performance and accuracy. This study presents a methodology applicable to the majority of low-rise, rectangular office structures. Future work would concentrate on carrying out comparison tests for different building forms and types while gradually improving the automation of the process to enable use of the appropriate accuracy level in assessing the crucial issue of energy-modelling input.

Computational fluid dynamics simulation of airborne COVID transmission in urban bus with different HVAC configurations

The HVAC systems in closed buses promote high particle spread. Lagrangian particle tracking simulations were carried out to evaluate airborne COVID transmission through droplets emitted by sneezing while Eulerian simulations were performed to account for the spread of aerosols emitted by breathing. The position of passengers as well as the effect of three HVAC configurations were evaluated. On one hand, it was concluded that large droplets can travel more than 3 m without being significantly affected by the inflow conditions, but small droplets are easily dispersed by the airflow, and many of them are captured by the HVAC systems. On the other hand, the HVAC systems quickly spreads aerosols along the whole of the bus, increasing the average risk for all passengers, but sensibly reducing the high local risks observed under motionless inflow conditions. The transmission risk was calculated by applying the Wells-Riley model, concluding that the transmission risk for a 20-min trip could remain below 0.5% if HVAC configurations with many inlet/outlet vents are implemented, and the passengers remain in silence and wear face masks.

Operating cost comparison of state-of-the-art heat pumps in residential buildings across the United States

With increasing concerns about the long-term global warming effect of HFC refrigerants, low-GWP refrigerants and non-vapor compression heat pumps are gaining attention to be the replacements for current vapor compression heat pumps that rely on HFCs. In addition, advanced heat pump solutions, such as heat pump water heaters, cold climate heat pumps, and low-GWP heat pumps are emphasized by regulators to make the heat pump market cleaner, more efficient, and more affordable. However, current research efforts lack comparisons of the new technologies under realistic building loads, climate conditions, and utility rates. In addition, combinations of emerging technologies have also not been considered. This study developed a methodology to systematically evaluate conventional and emerging space conditioning and water heating technologies both from performance and operating costs points of view. This study analyzed eight HVAC configurations for space heating, cooling, and water heating in terms of annual operating cost when coupled with an actual building affected by weather conditions. The eight HVAC configurations covered advanced solutions such as heat pump water heaters, ground source heat pumps, cold climate heat pumps, and membrane heat pumps, and they were compared with traditional vapor compression heat pumps and gas furnaces. The operating cost assessment was conducted based on building energy simulation using the real utility structure. The results revealed the trade-offs between HVAC combinations for the eleven climate zone covered in this study. The two-stage cold climate heat pump can save 10%–20% heating costs than single-stage heat pumps in cold regions. A membrane evaporative cooler can provide cooling cost savings in eight out of the eleven climate zones analyzed. A gas furnace should only be used in cold places where the electricity price per kWh to gas price ratio is higher than 3. HPWH should be recommended to places where the electricity price to gas price ratio is below 3.

Innovative metrics to evaluate HVAC systems performances for meeting contemporary loads in buildings

The significant impacts of the building sector ask for an urgent transition, which will be profoundly shaped by the HVAC sector. Due to recent energy demands modification, strongly associated to climate change consequences, buildings are asked to be equipped with HVAC systems capable of satisfying in a cost-effective way even contemporary space heating and cooling demands; in this context, the polyvalent heat pump (PHP) is recognized as a promising solution, being able to serve both requests simultaneously and independently, differently from the more widespread reversible heat pumps. However, despite the potentialities that the PHP could offer, still few efforts have been reserved to it in literature and existing metrics have proven not to be able to evaluate the capabilities of HVAC systems in meeting contemporary loads. Therefore, to fill this gap, through the development of a proper numerical model to investigate and simulate diverse systems operations on a common basis, the paper aims to develop new indicators able to include the assessment of the contemporaneity of request. To this purpose, the research: (i) proposes innovative technical indicators able to value PHPs performances, with particular attention to the assessment of the hours with contemporary space heating and cooling demands; and (ii) compares PHPs with other all-electric HVAC configurations using ad-hoc metrics, extending the discussion to other relevant domains, covering financial and environmental spheres. Thanks to the applicative study, the paper demonstrates the efficacy of the proposed indicators to evaluate the performances of HVAC systems for meeting contemporary loads in buildings, succeeding in valuing the technologies able to provide simultaneous heating and cooling services using a single unit. In addition, results highlight that PHPs can be considered a good trade-off from a multi-domain standpoint, emphasizing how this technology can be useful to drive the transition towards the electrification of thermal uses.

Cost-optimal nZEB HVAC configurations with onsite storage

By 2021, all new buildings in the European Union must be nearly zero-energy buildings in order to contribute to the achievement of the EU-CO2 neutrality by 2050. As the technical options to achieve highly-efficient building envelopes are available and well-known, there is no doubt that the most promising Heating Ventilation and Air Conditioning systems will include heat pumps and photovoltaic panels. However, there exist ongoing discussions on the optimal system layout and the integration of storage to achieve nZEB. In particular, there are some good arguments in favour of very low demand, while contrariwise also high flexibility is seen as an important feature to enable so-called grid-reactive operation of the building stock. Integration of onsite storage and its influence on the energy demand of the buildings and the corresponding electric load profile with focus on peak power is investigated.

Selecting HVAC systems to achieve comfortable and cost-effective residential net-zero energy buildings

HVAC is responsible for the largest share of energy use in residential buildings and plays an important role in broader implementation of net-zero energy building (NZEB). This study investigated the energy, comfort and economic performance of commercially-available HVAC technologies for a residential NZEB. An experimentally-validated model was used to evaluate ventilation, dehumidification, and heat pump options for the NZEB in the mixed-humid climate zone. Ventilation options were compared to mechanical ventilation without recovery; a heat recovery ventilator (HRV) and energy recovery ventilator (ERV) respectively reduced the HVAC energy by 13.5% and 17.4% and reduced the building energy by 7.5% and 9.7%. There was no significant difference in thermal comfort between the ventilation options. Dehumidification options were compared to an air-source heat pump (ASHP) with a separate dehumidifier; the ASHP with dedicated dehumidification reduced the HVAC energy by 7.3% and the building energy by 3.9%. The ASHP-only option (without dedicated dehumidification) reduced the initial investment but provided the worst comfort due to high humidity levels. Finally, ground-source heat pump (GSHP) alternatives were compared to the ASHP; the GSHP with two and three boreholes reduced the HVAC energy by 26.0% and 29.2% and the building energy by 13.1% and 14.7%. The economics of each HVAC configuration was analyzed using installation cost data and two electricity price structures. The GSHPs with the ERV and dedicated dehumidification provided the highest energy savings and good comfort, but were the most expensive. The ASHP with dedicated dehumidification and the ERV (or HRV) provided reasonable payback periods.

HVAC solutions for energy retrofitted hotel in Mediterranean area

To meet the European targets for achieving high-performing buildings, the refurbishment of the existing building stock and, in particular, of historical buildings represents a great challenge.The research aims at identifying the most energy-effective HVAC configuration for retrofitting historical hotels in Mediterranean area, where the objective is to minimize the consumptions for both space heating and cooling. A Reference Building for an historical hotel was simulated in five Mediterranean cities and different HVAC solutions were assessed, using EnergyPlus software coupled with tools specifically set to emulate the energy behaviour of certain HVAC technologies, aiming to highlight the most efficient alternative.

An exergy-based multi-objective optimisation model for energy retrofit strategies in non-domestic buildings

While the building sector has a significant thermodynamic improvement potential, exergy analysis has been shown to provide new insight for the optimisation of building energy systems. This paper presents an exergy-based multi-objective optimisation tool that aims to assess the impact of a diverse range of retrofit measures with a focus on non-domestic buildings. EnergyPlus was used as a dynamic calculation engine for first law analysis, while a Python add-on was developed to link dynamic exergy analysis and a Genetic Algorithm optimisation process with the aforementioned software. Two UK archetype case studies (an office and a primary school) were used to test the feasibility of the proposed framework. Different measures combinations based on retrofitting the envelope insulation levels and the application of different HVAC configurations were assessed. The objective functions in this study are annual energy use, occupants' thermal comfort, and total building exergy destructions. A large range of optimal solutions was achieved highlighting the framework capabilities. The model achieved improvements of 53% in annual energy use, 51% of exergy destructions and 66% of thermal comfort for the school building, and 50%, 33%, and 80% for the office building. This approach can be extended by using exergoeconomic optimisation.

Replicability of nZEBs on Real Estate Market in Mediterranean Countries

According to the recast of the Energy Performance of Buildings Directive and its target for the large-scale increase of nearly-zero energy buildings, nowadays a challenging task is the definition of standard high performing building types depending on location and specific climate conditions. The widespread replicability of nZEB types on the current real estate market could implement nZEB design scenarios attractive and affordable for construction companies and private investors. In particular, this research focuses on the definition of replicable HVAC system configurations with different features and efficiencies starting from a reference building located in a Mediterranean country. The configurations were applied to CorTau House, an nZEB under construction in Piedmont Region, a typical situation of European Mediterranean country where both winter and summer loads, together with humidity, have to be carefully controlled. Building envelope and HVAC system design were matched in order to optimize energy performance and indoor thermal comfort. The HVAC configurations, able to meet nZEB targets and to ensure optimal indoor comfort conditions, were combined with a performing building envelope, made of local construction materials, in order to assess which of them is more energy effective and economically viable. Cost-optimal types were identified and prospective replicability on building market was speculated. Finally, differences between private investor's and company construction's perspectives were discussed.

Model Development and Identification for Fast Demand Response in Commercial HVAC Systems

Large commercial HVAC systems are attractive targets for fast demand response (DR) applications, e.g., integrating time-intermittent renewable generation. By leveraging the communications in the building automation system (BAS) already present in most buildings, large commercial HVAC systems provide easier access to a large controllable resource than aggregating a large number of small residential loads. However, large commercial HVAC systems are complex with many variables, many end point controllers, and several internal control loops that interact with each other. In addition, the existing fleet of large commercial buildings is diverse with many different HVAC configurations and BAS architectures. Capturing these buildings as DR resources requires a method to greatly reduce the complexity of the HVAC DR control and is general and flexible enough that it can be easily deployed across the diverse fleet of existing buildings. We create such a DR control by developing a system model that uses a single state variable instead of the several hundred variables in a commercial HVAC system. The model includes a small number of system parameters, and we demonstrate how their values can be determined via system identification measurements. Finally, we test our model on a large commercial HVAC system to investigate its control performance.

Simulation and energy efficiency analysis of desiccant wheel systems for drying processes

In drying processes it is necessary to appropriately control air humidity and temperature in order to enhance water evaporation from product surface. The aim of this work is to investigate several HVAC configurations for product drying based on desiccant wheels, in order to find systems which reach high primary energy savings through the appropriate integration of refrigerating machines, adsorption wheels and cogenerative engines. Simulations are carried out for different values of sensible to latent ambient load ratio and the effect of ambient and outside air conditions is evaluated for each configuration. It is shown that primary energy savings can reach 70–80% compared to the reference technology based on a cooling coil. With respect to works available in literature, the results of this study keep a general approach and they can be used as a simple tool for preliminary assessment in a wide range of applications.

Optimization of hybrid – ground coupled and air source – heat pump systems in combination with thermal storage

Ground coupled heat pumps are attractive solutions for cooling and heating commercial buildings due to their high efficiency and their reduced environmental impact. Two possible ideas to improve the efficiency of these systems are decoupling energy generation from energy distribution and combining different HVAC systems. Based on these two ideas, we present several HVAC configurations which combine the following equipments: a ground coupled heat pump, an air to water heat pump and a thermal storage device. These HVAC configurations are linked to an office building in a cooling dominated area in order to evaluate in these conditions the total electrical consumption of each configuration to obtain which one satisfy the thermal demand more efficiently. The results of our simulations show that the electrical energy consumption obtained when the system employs a suitable configuration is of around the 60% compared with an HVAC system driven by an air to water heat pump and around the 82% compared with an HVAC system driven by a ground coupled heat pump.