Connecting, Nurturing, Creating for Sustainable Environment

Energy Efficient Retrofits Guide: Other Non-modelled Initiatives
   

2.4.23 Retro-commissioning ("RCx")

Retro-commissioning (“RCx”) is a systematic and continual process to evaluate an existing building’s performance, identify opportunities for operational improvements, and bring the building stock up to defined performance standard. This process aims to fully utilise opportunities, methods and adjustments to improve existing building equipment and systems for better energy performance, often without incurring any capital costs.

A typical RCx routine includes i) collecting building usage and equipment data; ii) analysing data to check whether equipment and systems are functioning properly to meet design or users’ requirements; iii) fine-tuning of building equipment and control systems for improved energy performance; and iv) periodic monitoring and verification of equipment and systems.

The underlying premise is that most buildings lose up to 30% of their efficiency in the first three years of operation[1]. This can be due to changes induced by addition, alteration and improvement works performed in the building, drift off from control set points, reduced accuracy or sensitivity of sensors, or substandard maintenance.

RCx can involve actions such as calibrating control sensors, adjusting timers and clocks, optimizing control sequences, adjusting lighting level, reviewing control programmes to suit operations, and more.

On average RCx can reduce a building’s energy consumption by between 7-22%, with actual energy savings highly dependent on the building’s original existing conditions. More information about RCx and RCx case studies can be found in EMSD’s Technical Guidelines on Retro-commissioning[2].

Advantages

  • little to no cost depending on the scale of work, thus the payback period will be short
  • prolongs equipment life and reduces the chance of equipment or system failure
  • enhances documentation of buildings’ data

Considerations

  • energy and cost savings will be dependent on building conditions
  • RCx is a continuous process, so building equipment and controls need to be monitored, checked and adjusted regularly to ensure their optimal energy performances 

2.4.24 High Efficiency Gas-fired Cooking Appliances


Image source: The Hong Kong and China Gas Company

Cooking appliances, in general, waste considerable amounts of energy as they are often not well-insulated or enclosed, and will lose heat to the surrounding environment. For example, a pot on an open stove only uses 20% of the energy in the gas being burned[3]. Therefore, the key to increasing energy efficiency is to retain the heat inside the appliance and reduce the energy wastage via heat recovery technologies.

For instance, a high efficiency gas steamer[4], with a double water tank design that makes use of a heat exchanger, reuses waste heat from steam generation to preheat water, so less energy is needed to boil water. In a particular case, compared to the traditional steamer, the new steamer reduced exhaust gas temperature by 50%, decreased indoor temperature by 2°C and produced less noise[5]. It also consumed 20% to 30% less energy, translating to HKD$20,000 savings per month and costs similar to a traditional steamer[6].

Furthermore, gas steamers/hot water supply has higher energy end-use efficiency than their electric counterparts from a lifecycle perspective (production, transmission and appliance usage)[7] and they have lower carbon emissions as the towngas feedstock is from naphtha, natural gas and landfill gas.


2.4.25 Radiant Chilled Ceiling Systems (Chilled Beams)


Image source: Stylepark Plafotherm® heated and chilled ceiling

The Radiant Ceiling Cooling system is a water-based cooling system that uses ceiling cooling panels to absorb heat in the forms of radiation and convection, and a chilled water pipe system to transfer the heat out. The chilled water pipes are laid behind false ceiling panels. Such a system separates cooling from the ventilation system and allows additional adjustments to improve indoor air quality, for instance, control fresh air intake and pump flow according to actual demands.

In hot and humid climates, a separate air intake system can be installed to dehumidify indoor air and to avoid water vapour condensation on chilled water pipes.

Case Study – Chilled Beams

An office building on Lantau Island near the Hong Kong International Airport had a chilled beam cooling system (system) installed in part of the building in 2011. This was in an area of 850 m2 hosting nearly 60 staff. With the success of the initial phase of the retrofit, the chilled ceiling has since been expanded to an area of 1200 m2.

The chilled beam cooling system consists of a centralised system which includes a primary air handling unit to dry and pre-cool fresh air, a heat exchanger to raise the chilled water temperature, a set of secondary pump system to supply chilled water, and a set of smart central control system. Local systems include zoned chilled water valves, fresh air control dampers, and chilled ceiling panels.

With the chilled beam cooling system, chilled water temperature can be set higher, at 10 – 15˚C compared to 5 – 7˚C in a fan coil unit system. Since there are no fan coil units, no energy is needed to power the fans and no waste heat is generated from fan motors. Furthermore, fresh air intake and pump flow can then be determined according to actual demand. This retrofit has resulted in an energy saving of more than 40%, compared to the previous conventional fan coil unit system.

Beyond saving energy, other benefits were also observed as a result of the retrofit. The office background noise level was reduced from 54.9 dB to 38.5 dB; the reduced space requirement compared to fan coil unit systems allows for a higher ceiling height; there is a 90% reduction in time needed for routine maintenance of the cooling system as there is no need to clean false ceiling air ducts, and the system parameters of the system can be remote-controlled by maintenance staff through mobile devices; and indoor air quality was improved.

 

Information provided by Swire Pacific, HAECO


2.4.26 Resizing Plumbing and Drainage Pumps

Pumps are a relatively cheap type of equipment but they consume significant amounts of energy. It is not uncommon for buildings to install oversized pumps that exceed the actual need of the building.

For instance, a building may have a pump to transport domestic water from ground up to a water tank on the rooftop. These pumps typically operate for 2 hours a day to pump an entire day’s usage worth of water to the tank. Since pumping energy is directly related to the pumping height and flow rate, a pump can be sized to have a much smaller flowrate but operate longer hours to reduce pumping energy.

Another common example is chilled water pumps in chiller systems. They are also often oversized, so reducing pump size can save significant amounts of energy. 


2.4.27 Task Lighting


Image source: Contract Office Reps Southern California

Task lighting ensures sufficient light levels on targeted working surfaces by illuminating directly over the specific areas. In addition, users can optimise lighting levels and angles according to their own needs. This helps user focus and perform tasks like reading and writing better, and will reduce eyestrain.

With task lighting in place, the overhead (ambiance) lighting power can be decreased while keeping the same, if not higher, levels of productivity. This can be used in conjunction with “Reduced Illuminance to 300 lux” mentioned in Section 2.4.4


2.4.28 District Cooling System

A district cooling system (“DCS”) works in a similar way to centralised cooling systems in buildings, but at a much larger scale. A central chiller plant supplies chilled water (or other media) to multiple buildings through underground pipe networks. Buildings and individual users do not need to install chiller plants as they purchase chilled water from the DCS operator. As a result of not installing chiller plants in buildings, the space saved can be redesigned for other purposes, for example, recreational facilities or sky gardens[8].

The DCS at Kai Tak takes advantage of economies of scale as well as lower seawater temperatures. It is estimated that it will ultimately consume 35% less electricity compared to traditional air-cooled AC systems and 20% less electricity compared to water-cooled AC systems[9]. A DCS plant can also be designed to supply hot water to form a District Heating and Cooling System for areas that require hot water or heating systems. As a result of not installing chiller plants in buildings, the space saved can be redesigned for other purposes, for example, recreational facilities or sky gardens[8].

Case Study – Kai Tak District Cooling System

Construction works for the district cooling system at Kai Tak commenced in 2011, with the construction of two plant rooms, a seawater pump room and installation of some chiller equipment, and laying of partial seawater pipes and chilled water pipes. The district cooling system began operation in early 2013. It currently provides chilled water to the Kai Tak Cruise Terminal, a shopping centre, a government office building, EMSD headquarter, Children Hospital and two schools. The remaining construction works are expected to be built in phases to be in line with scheduled development of the Kai Tak Development. Ultimately around 40 kilometres of underground pipes will be laid and the system is expected to serve more than 100 non-residential buildings.

The district cooling system has a coverage area of 320 hectares in the ex-Kai Tak airport, and has a total design cooling capacity of 284 megawatts of refrigeration, or 80,800 RT. This capacity translates to a cooling supply for 40 30-story high commercial buildings. The district cooling system comprises two central chiller plants – the North Plant and the South Plant. The advantage of having multiple plants is that the distance between chiller plants and consumers is reduced, hence cooling loss during conveyance is also reduced. The chilled water pipes have a 65mm insulation layer and buried underground to further help minimise cooling loss. According to a study by EMSD, the district cooling system is estimated to consume 35% less electricity compared to traditional air-cooled air-conditioning systems, and 20% less electricity compared to individual water-cooled air-conditioning systems. Ultimately, it is estimated the Kai Tak district cooling system will achieve an annual electricity saving of 85 million kWh, and a corresponding reduction of 59,500 tons of carbon dioxide emissions per year.

The district cooling system utilises sea water as a condensing medium to produce chilled water at the central plants, rejecting waste heat into the sea. This design is more efficient than traditional cooling tower option as seawater has lower temperature and helps to reduce the urban heat island effect in the Kai Tak area.

Most buildings served by the Kai Tak district cooling system are new build, but existing buildings can also be connected to the system, as seen in the case of EMSD Headquarters. This was connected to the system, replacing its chiller plant in mid-2017.

 

Information provided by Hong Kong District Cooling

 

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