by François Durier (CETIAT)
Reducing the energy consumption of heating and cooling systems in buildings requires:
- to reduce building heating and cooling needs, via high performance building envelopes, intelligent controls (management of set point temperatures, energy storage strategy, ventilation rates, etc.), energy efficient behaviour of occupants, etc.
- to improve the nominal energy efficiency of heating/cooling generators (boilers, heat pumps, air conditioners, chillers, etc.) and systems (heat recovery, intelligent controls, etc.)
- to improve the energy efficiency of heating/cooling systems in operation: this relies on the good quality of installation, on appropriate controls and occupants behaviour, and on regular maintenance of the systems.
This overview paper is focusing on the importance of the good quality of installations for heating and cooling systems in buildings in order to improve their energy efficiency. The performance of heating and cooling systems depends on how the components are sized, matched, installed, and maintained. Weak points in this quality chain can lead to performance losses (i.e. decrease of capacity and/or energy efficiency).
Quality of heating and cooling installations is stimulated by commissioning
The quality of installation of heating and cooling systems is often considered as being linked to their commissioning. Commissioning of buildings, including commissioning of heating and cooling systems, was defined and documented by Annex 40 of the Energy in Buildings and Communities (EBC) programme of the International Energy Agency (IEA).
According to Annex 40 report (2010), commissioning includes a series of actions such as clarifying system performance requirements, auditing actions to realise the performance, writing documentation, and verifying that the system enables proper operation and maintenance through functional performance testing. These actions ensure systems to be "designed, installed and functionally tested and […] capable of being operated and maintained to meet owner's project requirements from viewpoints of environment, energy and facility usage".
The Horizon 2020 QUANTUM project (2016-2019) found that poorly commissioned and operated building management systems are often responsible for a notable part of the gap between calculated and actual energy performance of the European building stock. This is often caused by the lack of appropriate and coherent quality management systems. The project intends to develop a practical management process to support commissioning, as explained in the BUILD UP webinar "Quality management within building commissioning" (2017).
Quality management process through the building life cycle (Source: QUANTUM project)
These examples show that commissioning stimulates the quality of the installation works and allows to identify and correct defects, if any.
However, commissioning is not yet widely used, as shown in a post from a BUILD UP blog, and in a workshop at CLIMA 2016 conference, organised by REHVA (Federation of European Heating, Ventilation and Air Conditioning Associations).
Commissioning improves energy efficiency
Annex 47 of the IEA EBC programme, entitled "Cost-effective commissioning of existing and low energy buildings", produced a report (2010) on commissioning cost-benefit. No unique clear conclusion was derived from the commissioning data of several public and commercial buildings, due to difficulties to assess the energy savings and/or the costs of the commissioning process. Nevertheless, authors state that "commissioning of new and existing buildings has been shown to reduce energy usage and can also produce non-energy related benefits such as improved occupant comfort", with short investment payback periods compared to other initiatives (e.g. installation of high efficiency equipment or installing photovoltaic systems).
Commissioning cost-benefit and persistence of savings (Source: IEA-EBC Annex 47)
A presentation (2014) by REHVA mentions cost-benefit data for commissioning as follows: cost between 0.3 % and 0.7 % of the total development cost, energy cost savings between 5 % and 15 %, increased staff productivity, lower maintenance costs, environmental protection.
It should be noted that the results of a cost-effectiveness analysis depends on several factors (initial quality of the installation, commissioning methodology, energy costs) and that it remains difficult to reach general conclusions about the cost-effectiveness of commissioning from published data for some buildings in some countries and at a given time period.
Impact of commissioning faults
Evaluating the positive impact of the good quality of the heating and cooling installations can result from an assessment of the energy waste due to poorly installed and/or maintained systems.
This was for example investigated for heat pump systems in the Annex 36 of the IEA Technology Collaboration Programme on Heat Pumping Technologies. Annex 36 (entitled "Quality installation/quality maintenance sensitivity studies") evaluated how poorly installed and/or maintained heat pumps - i.e. with deficiencies in their commissioning – lead to inefficient performance and hence waste energy.
In this project, works by the National Institute of Standards and Technology (NIST, USA) analysed the impact of commissioning common faults on heat pump performance installed in a single-family residential house under different climates.
Through annual simulations, the study found that duct leakage, refrigerant undercharge, oversized heat pump with nominal ductwork, low indoor airflow due to undersized ductwork, and refrigerant overcharge have the most potential for causing significant performance degradation and increased annual energy consumption. The effect of simultaneous faults was found to be additive, little changed relatively to the single fault, or well-beyond additive.
How to reach quality
A report (2016) from the European project QUALICHeCK identified reasons for the low quality of construction and installation works. These include: poor specifications of projects, standards or regulations, lack of competences, critical economic conditions and lack of control. Several examples are presented for heating systems (heat pumps, solar thermal systems).
Towards improved quality of the works (Source: QUALICHeCK project)
One of the main conclusions of the QUALICHeCK project was that heat pumps, solar thermal and other renewable energy technologies showed good performance if certified installers schemes were applied, and that improved quality can be reached by tools and schemes such as: training and certification, guidelines and quality insurance procedures, systematic commissioning and maintenance, continuous performance monitoring and third party control.
A report from the QUANTUM project (2016) analyses reasons for the quality gap, i.e. the amount of deviation between a planned and an actual level, at different stages of the construction. They include: wrong understanding of client needs, poor design, building performance modelling/simulation errors, non-optimal HVAC system installed, lack of skilled workforce, lack of commissioning, etc. Existing laws, guidelines and standards for quality management in buildings are also listed, together with existing services.
Regardless the ways used to reach it, quality of installed heating and cooling systems in buildings is a key point for energy efficiency.