M.Masoero, C.Silvi, J.Toniolo
Dipartimento Energia, Politecnico di Torino
Air conditioning systems can account for up to 50% of the energy used in a building, and are therefore specifically targeted in the new legislation. The Energy Performance of Buildings Directive (EPBD) was established in 2002 (Directive 2002/91/CE). Article 14 of the 2010 EPBD recast, which is aimed at reducing CO2 emissions within the building sector, requires a regular inspection for HVAC systems with more than 12 kW cooling capacity. However, so far only a few Member States have transferred this prescription into national law.
HARMONAC (Harmonizing Air Conditioning Inspection and Audit Procedures in the Tertiary Building Sector) was a project supported by the Intelligent Energy Europe initiative in 2007-2010. The project was funded to provide actual energy consumption data on HVAC system in Europe and to establish standard inspection tools and criteria. Some results from HARMONAC project were used to recast the EPBD at this actual form (EPBD, Directive 2010/31/EU). A new project, called iSERV continuous monitoring and benchmarking project, was funded in 2011, specifically targeted to put the HARMONAC results in practice on a wider scale, with a specific emphasis on energy monitoring of HVAC systems.
Objective of the work
The IEE HARMONAC project was developed to reach a number of clear aims:
To produce a series of HVAC inspection procedures, to be applied by member states in the framework of EPBD Directive;
- To provide new field-tested materials and tools to aid Inspectors in the inspection process;
- To understand more clearly how HVAC systems consume energy;
- To assess the opportunities for energy savings.
The project ensured that the information was presented to the main actors involved in HVAC systems mandatory inspection. The purpose was to help the defined bodies to produce regulations and legislation in this area that maximize the energy and cost benefits to the system owners, and hence to Europe, from the time and money invested in these inspections.
A clear and unexpected result achieved during the development of the project was the clear knowledge that continuous monitoring will be helpful in HVAC inspector work, and could represent the basis for reliable benchmarking of HVAC systems.
To achieve the project aims the energy consumptions of the HVAC systems and their components have been monitored in sub-hourly detail. Two types of investigations were carried out: during Case Studies systems are monitored for at least one year, while in Field Trials monitoring take place for a short time period (variable between 7 and 90 days). In other words, a File Trial basically means the inspection of an HVAC system, including pre-inspection and on-site inspection. A Case Study consists of such inspection combined with long-term monitoring and analysis of energy saving potentials, based on measurements and/or simulations.
The main idea is that the Case Studies helped to understand the HVAC consumption difference due to seasonal variation and major building/system refurbishment (e.g.: chiller substitution, windows substitution, etc). On the other hand the Field Trials were intended to simulate limited time on-site inspections and to analyze specific HVAC system aspect (e.g.: Control strategy, Chiller efficiency, etc). The majority of Field trials were enhanced by additional measurements which go beyond the current Inspection requirements, to enable further insights to be obtained about the effectiveness of the inspection process.
The Case Studies were carried out studying the energy use, operation and maintenance regime of about 40 Systems around Europe. The Case Studies were intended to analyze in as much detail as possible where the energy was being used, what energy conservation opportunities (ECOs) there were, and to quantify these ECOs where possible. This was undertaken within the project constraints and for over at least a year for the majority of the systems. The project was directed to take existing AC Inspection Methodologies and turn them into a specific HARMONAC Methodology, which allowed the elements of an inspection to be analyzed in terms of time taken, ECOs identified, and likelihood of achieving energy savings. During the project it was found that this approach also allowed ECOs and their savings to be roughly associated with inspection items as well as allowing teaching package sections to be referenced as help sections.
Further concern of HARMONAC project was directed to Field Trials. The range of ECOs identified from the Field Trials was compared to those found from the Case Studies so that the effectiveness of the Inspection process in identifying all the ECOs that potentially existed could be gauged. The Field Trials and Case Studies are complementary, as without the Case Studies we would not have the detailed information needed to understand how AC systems generally consume energy, and therefore the additional ECOs that may be present in reality that the Inspection procedures are not finding – along with the relative importance of these ‘missed’ ECOs in the overall energy use of AC systems. The Field Trials are crucial, however, to assessing the realities of the practical implementation of Inspection procedures on real systems, and which ECOs are likely to be found, and which are likely to be missed.
Findings from Field Trials and Case Studies
There are some practical limitations to an inspection in terms of the time available to undertake it and its inherent ‘snapshot-in-time’ nature. During the project different tools were developed and tested to increase understanding of the potential energy savings to be achieved in the systems inspected, and hence increase the value of the inspection. Nevertheless it was made clear that without reliable energy consumption data it is almost impossible to achieve reliable ECOs evaluation and reliable ROI (Return of Investment) associated to those ECOs.
Five Case Studies and fourteen Field Trials have been carried out in Italy. The Case Studies and Field Trials have been organized by Politecnico di Torino. Most Italian Case Studies were carried out in large office buildings; one Case Study examined a retirement home. The examined buildings are located in Northern Italy, in the cities of Torino, Genova, and Trieste. The conditioned floor areas of the buildings range between 4800 and 24000 m2. HVAC systems analyzed are of different types:
• All air (CAV)
• All air (VAV)
• All water (with fan coils)
• Air and water (with active chilled beams or fan coils)
• VRF air to air reversible heat pump
Central heating and cooling production includes conventional electric chillers (air cooled or water cooled) coupled with gas-fired boilers, absorption chillers coupled to biomass combustion boilers, tri-generation units with IC engines, and VRF heat pumps.
Building structure typologies are quite diversified: CS IT-5 is a XVII century masonry building, largely rebuilt in reinforced concrete after WW-II; CS IT-3 is an early XIX century building with bearing masonry walls (average thickness 50 cm); CS IT-2 is a technology park built in the 1990s with a number of high energy performance envelope technologies (green roofs, ventilated façades, low U-value glazing, etc.); two CSs (IT-1 and IT-4) are high-rise office towers with curtain walls and large glazed surfaces.
Table 1: Italian Case studies overview
Results from a sample Case Study
The case study addressed the energy analysis for the installation of an absorption chiller coupled to a Combined Heat and Power (CHP) generator. The preliminary analysis assumed that the waste heat from CHP system should be directed to an absorption chiller. The base cooling load (kWh) then can be covered by the absorption unit, while the peak load would be provided by the existing electric chiller. Preliminary simulations to address the economic feasibility of the installation indicated a 75.5% energy saving. The graph in Figure 1 shows the cumulate electrical load of the two chillers, during the first season and during the second season. The overall result is a 20.8% saving on total chiller electric energy consumption. This is a good operational result, but it is dramatically lower than the 75.5% expected from the simulation.
The major explanation for the different values is that in current operation the absorption unit is not working as stated in the simulation. The nominal performance of the unit is calculated with inlet hot water at 90°C. In the building the hot water to the absorption unit is provided by an IC engine rated at 1 MW electric power. The CHP system was installed before the chiller; its circuit was designed for a maximum temperature of 90°C. During operation, when the water temperature reaches 85°C, the system stops due to safety valves. For this reason the inlet water to the absorption unit is delivered at 83-84°C, and the COP of the unit decreases.
The other reason that implies a huge difference between simulation and monitoring is the system schedule. In the simulation the absorption chiller schedule was not considered. In the real plant, the CHP unit is turned on just from 8:00 AM to 7:00 PM for economic reasons. During this time the electric energy produced by the CHP is sold at the maximum rate (peak hour). This implies that the absorption unit cannot be turned on before 8:00 AM. Moreover, the unit needs some time (almost one hour) to provide full performance.
Figure 1 Carpet plot of the chiller plant electric consumption. (The chiller plant includes the electric chiller, the absorption chiller and the chilled water circulation pumps).
The two seasons are not completely comparable, due to the complete substitution of the windows on the north façade. The refurbishment of the façade lowered the heating demand for the winter season, but raised the cooling load requested during Summer since the window retrofit reduced the night time free cooling effect. Substitution of windows with low permeability and low U-value ones should be carefully considered in respect of effects on cooling loads
The iSERV project, by collecting sub-hourly HVAC system energy use data from around 1600 HVAC systems in the EU Member States, is intended to demonstrate that a comparison with specific benchmarks will help the energy consumption reduction of HVAC systems.
To reach this objective, the project will be able to:
1. Provide the system owners feedback on energy use patterns;
2. Establish a detailed understanding of the energy consumption of European HVAC systems meeting specified end use activities;
3. Provide evidence-based information to HVAC system manufacturers, EU Member State Legislators, European Standards Bodies, Professional Building Services Bodies and HVAC system owner/operators on how to improve the in-use energy efficiency of HVAC systems.
According to article 14 of the 2010 EPBD recast, it will be possible to allow owner/operators of systems showing good energy performance to avoid needless Inspections.
The core of the project is a web-based data collection and reporting application for the EU member state HVAC systems. The application is fully web-based and requires only an internet connection, the use of standard software. This makes it ideal for use as such tools are all free to end users. The application itself is also free to use.
End users of the application receive their own secure login details and are able to enter their own data manually or automatically if their data collection systems already allow this. This process involves entering the data directly via a manual interface or uploading a spreadsheet with manually/automatically read data to the application. These data are usually supplied in the industry standard .csv format.
The definition of an HVAC system for iSERV is: “An area served by separate Ventilation and AC components which are individually metered such that the energy consumption of the AC and Ventilation systems can be physically separated from other VAC systems. Heating systems do NOT need to be separate to each of these areas”. Under this definition a building may have more than one system.
The database is sized for 1600 systems, with 125 different readings (meter or sensor) and recordings at 15 minutes interval. This allows for a greater number of readings (due to more meters/sensors or lower intervals) or more systems.
Users initially need to describe their building spaces in terms of floor areas, activities undertaken, etc., but little effort is then needed after this point other than to enter the consumption data at a minimum of monthly intervals. It is considered that the optimum interval is 15 minutes for automated systems, and, where possible and feasible, this should be the preferred method. The application is designed to allow them to either manually produce their own reports or to automatically run off a bespoke report when their data is entered. There is a data entry error notification function in the system to alert them to data problems as they enter the data.
The key to increased long-term energy efficiency in AC systems rests with making it cheaper for the owner to run their systems efficiently and to specify low energy equipment, than it is to just accept an Inspection. This implies Inspections should be expensive, and that there should be an alternative that rewards good energy management by allowing systems to avoid inspection if they achieve certain standards: specific benchmarks harmonized on building use and size. iSERV cmb project will provide benchmarks for specific building uses.