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Energy Efficient Retrofits Guide: HVAC - Air Side
   

2.4.10 Demand-controlled Ventilation (“DCV”)

Why?

§  significant energy savings
§  improves indoor air quality

Where does it work best?

Office Buildings (Types 1 & 2)

  • office areas that require fresh air supply

Hotel Buildings

Image Source: ASHRAE

Overview

As the building fabric improves and lighting/computer systems become more efficient, fresh air treatment has become the single largest cooling load in a modern building, so it has potential for significant energy savings.

DCV modulates ventilation rates to suit fresh air demands, so that energy can be saved by avoiding excessive cooling, and in some cases, heating and dehumidification, of air supplied to buildings. For example, the number of occupants and fresh air demand can be estimated by CO2 sensors that are typically located in occupied zones. The CO2 concentration set-point is typically between 800 and 1000 parts per million (ppm), and the system will automatically adjust outdoor air intake to maintain the CO2 set-point for optimal performance and meet fresh air demands.

Modelled Costs and Saving Potentials (assumptions are listed in Appendix A)

Demand-controlled Ventilation

Building Type

Office Type 1

Office Type 2

Hotels (Dining, Multifunction and Kitchen)

Hotels (Guestroom fan cycle)

Capital Cost (per m2 building area)

HK$158

HK$33

HK$4

HK$0.2

Payback Period (years)

3.9

0.6

0.5

0

Saving Potentials (per m2 building area)

Cost

HK$40/year

HK$58/year

HK$9/year

HK$11/year

Energy

36 kWh/year

51 kWh/year

8 kWh/year

10 kWh/year

Carbon

21 kg CO2-e/year

31 kg CO2-e/year

5 kg CO2-e/year

6 kg CO2-e/year

Advantages

  • technology is mature
  • significant energy savings
  • improves indoor air quality
  • reduced usage of belt drive can help extend equipment lifetime due to reduced wear and tear
  • buildings with direct fresh air-intake air handling units (AHUs) can adopt DCV easily

Limitations

  • higher capital cost if there are a high number of AHUs or fan coil units (FCUs), as air volume dampers and CO2 sensors will need to be installed
  • high capital cost to implement in hotels due to the large number of rooms

Additional Considerations

  • DCVs are most efficient in irregularly occupied office areas, e.g. meeting rooms
  • apart from using CO2 sensors, fresh air demand can also be measured by integration with intelligent building systems, e.g. staff card records or CCTV People Counting Systems
  • operational and maintenance considerations, e.g. recalibration of ventilation systems and CO2 sensors
  • re-commissioning will generally be required after installing DCVs
  • for buildings that are difficult to retrofit controls, or with a large number of rooms, like hotels, cycling (turning off fresh air supply during periods with low occupancy rates) will be a more feasible option

Relevance to Landlords and Tenants

  • landlords are primarily responsible for HVAC system upgrades
  • cost savings from reduced ventilation energy use are directly financially beneficial to landlords and potentially to tenants in the longer term

2.4.11 Electrically Commutated ("EC") Plug Fans

Why?

§  significant energy savings
§  long lifetime with low noise levels

Where do they work best?

Office Buildings (Types 1 & 2)

Hotel Buildings

Image Source: ebm-papst

Overview

Traditional air handling units (“AHUs”) and primary air units (“PAUs”) rely on a single belt driven centrifugal fan controlled by a variable frequency drive (“VFD”) motor. This allows control over fan speeds but the minimum fan power output is still 50% of a fan’s rated capacity.

Small brushless EC plug fans, which by themselves are around 5% more efficient than VFD motors, can be installed in an array to form a fan-wall. As multiple fans are used to produce the desired flowrate, individual fans can be shut off in part-load conditions to further reduce air flow, and therefore allowing energy saving levels beyond what VFD motors could do. 

Modelled Costs and Saving Potentials (assumptions are listed in Appendix A)

EC Plug Fans

Building Type

Office Type 1

Office Type 2

Hotels

Scenario

End-of-Life

Total Cost

End-of-Life

Total Cost

End-of-Life

Total Cost

Capital Cost (per m2 building area)

HK$84

HK$462

HK$4

HK$22

HK$5

HK$29

Payback Period (years)

9.6

52.6

2.2

11.9

0.3

1.6

Saving Potentials (per m2 building area)

Cost

HK$9/year

HK$1.9/year

HK$18/year

Energy

8 kWh/year

1.6 kWh/year

16 kWh/year

Carbon

5 kg CO2-e/year

1 kg CO2-e/year

10 kg CO2-e/year

Advantages

  • technology is mature
  • can be easily retrofitted into existing AHUs or PAUs, making plug fans a viable replacement for end-of-life motors
  • allow a larger degree of control over the fan speeds to save fan energy usage
  • extended lifetime as EC plug fans do not use belt drives in their operation
  • greatly reduced noise levels which can improve productivity in adjacent areas

Limitations

  • limited choice of suppliers that could be an issue for certain projects 

Additional Considerations

  • the energy saving performance is highly dependent on the capabilities of control systems and air delivery systems
  • existing air handling units can be retrofitted with plug fans

Relevance to Landlords and Tenants

  • landlords are responsible for HVAC system upgrades
  • cost savings from reduced ventilation energy use are directly financially beneficial to landlords and potentially to tenants in the longer term

2.4.12 Direct Current Fan Coil Units

Why?

§  significant energy savings
§  long lifetime with low noise levels

Where do they work best?

Office Buildings (Type 2)

  • general office areas that require fresh air supply 
  • core areas such as fire escapes

Hotel Buildings

  • guest rooms 
  • back-of-house (BOH) offices

Image Source: Euroklimat

Overview

Direct Current (“DC”) Fan Coil Units (“FCUs”) use DC motors instead of traditional alternating current (“AC”) motors. DC FCUs save energy not only by using a more efficient motor, but also by their ability to modulate air supply rates according to local zone cooling demands.

In traditional AC motors, fan speed does not have much impact on fan power consumption. In contrast, DC FCUs are very sensitive: a slight reduction in fan speed can result in significant fan power savings. Two-third of the energy used in fans can be saved with appropriate FCU controls.

DC FCUs are also a lot quieter and have longer lifetimes comparing to AC FCUs due to less vibration and heat. As to enhancing comfort, it is worth noting that when DC FCUs were first available in the market, they were mainly used in premium hotel bedrooms. 

Modelled Costs and Saving Potentials (assumptions are listed in Appendix A)

Direct Current Fan Coil Units

Building Type

Office Type 2

Hotel

Scenario

End-of-Life

Total Cost

End-of-Life

Total Cost

Capital Cost (per m2 building area)

HK$84

HK$153

HK$98

HK$134

Payback Period (years)

5.0

9.2

4.5

5.5

Saving Potentials (per m2 building area)

Cost

HK$17/year

HK$24/year

Energy

15 kWh/year

22 kWh/year

Carbon

9 kg CO2-e/year

13 CO2-e/year

Advantages

  • technology is mature
  • significant energy savings
  • extended lifetime as DC FCUs do not use belt drives in their operation
  • reduced noise levels

Limitations

  • higher capital costs than their AC counterparts
  • require additional wiring for controls

Additional Considerations

  • retrofitting existing FCUs to DC motors is now available in the market to reduce costs
  • suitable for areas where noise levels need to be low

Relevance to Landlords and Tenants

  • landlords are primarily responsible for HVAC system upgrades
  • cost savings from reduced ventilation energy use are directly financially beneficial to landlords and potentially to tenants in the longer term. Tenants benefit from reduced noise levels

Case Study – Fan Coil Unit

A In 2012, a hotel of 274 guest rooms in Sheung Wan installed a variable speed intelligent fan coil unit in each room during the construction phase of the new hotel building. Each fan coil unit consists of a permanent magnet, brushless, direct current motor, and comes with a corresponding control box and thermostat control system with return air duct temperature sensor.

The motor with permanent magnet is more energy efficient than the conventional fan coil units with alternating current motor. The thermostat system regulates fan speed automatically according to room temperature against the temperature set point. In addition, the thermostat system has a “quick cool” function, in which the motors operate at 5% above regular high speed capacity to achieve the desired room temperature quickly, then automatically lower the motor speed upon reaching the temperature set point.

Compared to the conventional fan coil units, the new units reduced energy consumption by 40% when operating at high speed, 66% when operating at medium speed, and 80% at low speed. On average, the energy consumption was reduced by 76%.

Additionally, the waste heat generated by the fan coil units were reduced as well. The operating temperature increase was reduced by 58% when operating at high speed, 87% at medium speed, and 95% at low speed. With the fan coil units operating 24 hours a day and with each unit operating at an average of 600 cubic feet per minute, the fan coil units allowed the hotel to save a total of 149,433 kWh of electricity per year. The resultant monetary savings are approximately HKD$194,263 per year, translating to a 2.12-year payback period.

 

Information provided by REC Engineering and Holiday Inn Express Hong Kong SoHo



2.4.13 Variable Refrigerant Flow for High Efficiency Direct Expansion

Why?

§  effective for large chiller plants
§  some buildings may already have existing building management systems

Where does it work best?

Office Buildings (Type 3)

  • office areas
  • areas that need air-conditioning day-and-night

Hotel Buildings

  • areas that may not have access to chilled water

Image Source: Cool Automation

Overview

Variable Refrigerant Flow (“VRF”) air conditioners typically consist of multiple indoor expansion units, which absorb heat, connected with an outdoor condensation unit that releases heat to the environment.

Traditional direct expansion (“DX”) systems are relatively low cost and energy efficient for small installations; they require simple installation and less ductwork comparing to chiller water/air systems. VRF systems not only reside on DX technology, but can also provide solutions to the limitations of older DX systems. For instance, a compressor in conventional multiple-split DX system must be turned on or off completely in response to a master controller, while a VRF system can adjust the flow of refrigerant to each indoor evaporator unit separately[1] through a variable speed drive driven compressor, allowing VRF systems to be very efficient especially in part-load conditions.

Modelled Costs and Saving Potentials (assumptions are listed in Appendix A)

Variable Refrigerant Flow (for Office Type 3 only)

Scenario

End-of-Life

Total Cost

Capital Cost (per m2 building area)

HK$51

HK$254

Payback Period (years)

1.3

6.4

Saving Potentials (per m2 building area)

Cost

HK$40/year

Energy

35 kWh/year

Carbon

21 kg CO2-e/year

Advantages

  • technology is mature
  • can provide heating or cooling depending on the installed system
  • tackles some of the limitations of traditional DX systems, such as lack of zone control and short lifetime

Limitations

  • higher capital cost than traditional DX systems
  • pipework replacement will normally require draining and re-filling the entire circuit with refrigerant
  • VRF systems have minimum size requirements
  • they also have shorter lifetime than chiller water systems

Additional Considerations

  • VRF systems will be very efficient in areas that require both cooling and heating
  • generally used when no centralised cooling systems are present (i.e. Type 3 Office)

Relevance to Landlords and Tenants

  • both replacement costs and cost savings will primarily be on the tenant-side


2.4.14 Intelligent Building Control Systems

Why?

§  effective for large chiller plants
§  some buildings may already have existing building management systems

Where do they work best?

Office Buildings (Types 1 & 2)

  • central chiller plant
  • energy management for the entire building

Hotel Buildings

  • guestroom management
  • central chiller plants
  • energy management for the entire building

Image Source: Ebusiness Strategies

Overview

Building management systems (“BMSs”) are fairly common in buildings, but are often treated simply as on/off control devices. Smart building controls collect building information and optimise building equipment for energy efficiency. They can be applied to various equipment, including but not limited to chiller plants and lighting systems (see the case studies below).

For instance, a chiller plant optimiser for improving chiller plant controls will calculate the best combination of chiller staging control, temperature set-point, number of pumps and cooling towers based on real-time cooling load, outdoor air temperature and humidity. The module can also calculate the time required to pre-cool the building in early morning based on weather conditions and previous operational data.

For hotels, an example of this can be an intelligent bedroom management system: if the hotel’s default temperature is 22°C, the system will set an unrented room’s set-point to 26°C and turn off all lighting and AV systems. The room air-conditioning will only be turned on again if the temperature exceeds 26°C. If the room is rented but not occupied, the system will change the set-point to 24°C, or any other temperature at the building manager’s discretion.

Modelled Costs and Saving Potentials (assumptions are listed in Appendix A)

Smart Controls for Chiller Plants

Building Type

Office Type 1

Office Type 2

Hotel

Capital Cost (per m2 building area)

100*

100*

38*

Payback Period (years)

10.5

8

3.0

Saving Potentials (per m2 building area)

Cost

10 HK$/year

13 HK$/year

12 HK$/year

Energy

8 kWh/year

11 kWh/year

11 kWh/year

Carbon

5 kg CO2-e/year

7 kg CO2-e/year

7 kg CO2-e/year

*Cost figures are less sensitive to building area changes than other options; figures above are for the sample studies

Advantages

  • can have significant energy savings for large chiller plants
  • buildings may already have BMSs with certain smart control features

Limitations

  • initial costs can be high
  • annual license fees may apply to smart control systems
  • limited usefulness for buildings without central chiller plants

Additional Considerations

  • since BMSs are typically not utilised to their full extent, building operators are recommended to explore control features offered by the existing systems before looking at an upgrade
  • these systems also collect useful operational data that can be logged onto an energy management platform, and utilised to look for additional energy saving opportunities via data analytics tools

Relevance to Landlords and Tenants

  • all upgrades in centralised operations are generally paid for by landlords and, in turn, primarily benefit landlords financially, however tenants should benefit in terms of comfort and potentially in the longer term as to costs

Case Study – Smart Lighting Controls

An office within a building in Tsim Sha Tsui installed smart lighting control system into their office in 2016.

The lighting control system is a cloud-based system that controls each light fixture individually. Through the cloud server, the user can assign instructions to the light fixtures, helping to optimise lighting use by spatial and time variations. Occupants can also use a mobile application to control the lights of the office. The system enabled automatic lighting on/off schedule and personalised granular control, so lights were only turned on where and when they are needed. The system was installed to control approximately 100 4-feet T5 tubes at the office.

Retrofitting this technology involves connecting a controller at each light fixture, and it takes approximately 5 minutes for each fixture controller installation.

Prior to installing this system, unoccupied areas were often illuminated even with one-third of the staff frequently working outside of the office. The installation of this system reduced daily energy cost by 53%.

The retrofitting of this technology can help achieve the largest energy savings in spaces with dynamic lighting usage, such as offices with low occupancy rates and non-desk bound staff. On the other hand, opportunities for energy savings would be less in areas with relatively static lighting usage patterns, such as lobbies or warehouses.

 

Information provided by En-track

 

Case Study 2 – Chiller Optimization

In 2015, the installation of a chiller plant control programme was completed in an office complex in Wan Chai, with the system controlling 6 water cooled centrifugal chillers, some of which are variable speed drive and some are constant speed drive. The programme features automatic control of the chiller operation, integrated control of start-stop sequence, and integrated control of chilled water supply temperature reset – all of which were manually controlled by the operator prior to the upgrade.

The start-stop sequence of the chillers are optimised in that during start up, VSD chillers are started first followed by CSD chillers, and during the shut-down process, CSD chillers are stopped first followed by stopping VSD chillers. This automated control helps to reduce energy consumption during start-stop in the mornings and evenings. The automatic chilled water supply temperature reset allows chilled water supply temperature to be adjusted more frequently to match the actual cooling load demand of the building. Overall, these optimization strategies approximately reduced the electricity consumption of chiller plant by 16%.

 

Information provided by SHKP and its property management subsidiaries

 

Case Study 3 – Smart Controls for HVAC Systems

In 2012, a smart control system for HVAC system was applied to a hotel of 274 guest rooms in Sheung Wan. The smart control system provides automated, real-time optimization of the energy consumption performance of HVAC system according to building load and local weather conditions through continuous monitoring and subsequent fine tuning of system operations. The application of the smart control system involves applying a software package of control algorithms to the equipment of HVAC system, and linking up with the existing building management system. Accordingly, the prerequisite to the applying this smart control system is a chiller with high-level interface, and a high-level interface with open protocol-type building management system.

Applying the smart controls for HVAC system in the hotel in Sheung Wan required putting in place additional sensors and an additional computer. The total initial cost of installing the smart control system was HKD$498,000. The smart control system reduced the energy consumption of the HVAC system by 27%, which translated to a 16.2% saving of the entire building’s energy consumption. The payback period of the energy optimization solution was 1.43 years. The energy savings were achieved while maintaining the same level of thermal comfort in the hotel.

The energy saving achieved from this smart control systems is dependent on the scale of the HVAC system and the length of the HVAC system’s operating time.

 

Information provided by REC Engineering and Holiday Inn Express Hong Kong SoHo


2.4.15 High Volume Low Speed (“HVLS”) Fans

Why?

§  simple installation
§  improved thermal comfort

Where do they work best?

Office Buildings (Types 1, 2 & 3)

  • lobby, circulation and communal areas
  • opne plan office areas

Hotel Buildings

  • guestrooms, lobby, circulation and communal areas
  • naturally ventilated areas

Image Source: Big Ass Fans

Overview

High-volume low-speed (HVLS) fans are mechanical fans with a large diameter rotating in low speed. Although HVLS fans do not directly reduce the room temperature, they produce a cooling effect by increasing air movement thus enhancing evaporation which cools the human body. As the overall air movement is more dependent on the diameter of a fan instead of its rotational speed, HVLS fans will create a larger cooling effect than small high-speed fans[2]. With HSLV fans, it is possible to increase the thermal set points for the space by approximately 2.2°C[3], or even 2.8 – 3.3°C[4], without compromising thermal comfort.

Another example is to use it in circulation areas, such as lobbies, in conjunction with natural ventilation for mixed mode ventilation. This would eliminate the need for air-conditioning for up to 6 – 8 months in a year. HVLS fans are also common in resorts and holiday hotels in places like Singapore. They are installed in hotel lobbies, bedrooms and semi-open areas.

Modelled Costs and Saving Potentials (assumptions are listed in Appendix A)

HVLS Fan

Building Type

Office Type 1

Office Type 2

Office Type 3

Hotel

Capital Cost (per m2 building area)

218

218

218

5

Payback Period (years)

10.6

11.5

23.8

11.1

Saving Potentials (per m2 building area)

Cost (HK$/year)

20

19

9

0.5

Energy (kWh/year)

18

17

8

0.4

Carbon (kg CO2-e/year)

11

10

5

0.24

Advantages

  • improve thermal comfort for occupants
  • energy can be saved through reduced air conditioning use
  • they produce less turbulent air flow, resulting in less disturbance for an office environment
  • work well with buildings with access to natural ventilation
  • low maintenance requirements
  • relatively simple installation

Limitations

  • they work best in spaces that have high or open (exposed) ceilings

Additional Considerations

  • noise can be a concern, and quieter fans will typically be more expensive
  • there are ideal installation heights that should be considered
  • larger fans are more effective than smaller fans
  • smaller fans can be used in offices, however head height should be considered for safety – generally fans should be installed at least 3m from the ground

Relevance to Landlords and Tenants

  • generally, reduction in cooling energy in tenant spaces will result in cost savings for the landlord, as tenants simply pay a fixed charge that covers cooling amongst other things
  • therefore this technology will be directly beneficial to the landlord in terms of costs, unless tenant pays for actual cooling (as assumed in Type 3 offices), but in the longer term tenants may benefit financially

Case Study – High Volume Low Speed Fans

The Zero Carbon Building in Kowloon Bay was built in 2012 with a total of 15 high volume low speed ceiling fans installed: 10 eight-bladed fans with gearless direct-drive motors with diameters of 95 inches, 3 three-bladed fans spanning 52 inches, 1 three-bladed fan spanning 60 inches, and 1 eight-bladed fan with a gearbox with a diameter of 95 inches. 3 fans are located in the office and operates in conjunction with chilled beams and underfloor displacement cooling to cool the area. The other fans operate with the underfloor displacement cooling system to cool the remaining areas of the building, including exhibition areas and a multipurpose hall. The fans are in operation throughout most of the year.

The fans have airfoil and winglet designs for efficient airflow by eliminating vortex formation at airfoil tips. The increased airflow enhances evaporation rates for comfort and reduces perceived temperature by around 2 degrees Celsius. The fans further improve ventilation and distribution of conditioned air, reducing the demand for air conditioning.

It is estimated that the high volume low speed fans reduce the building’s cooling energy consumption by 14%, compared to solely relying on the other components of the building’s cooling system to achieve the same cooling effect.

 

Information provided by CIC - Zero Carbon Building, Big Ass Fans



2.4.16 Carbon Monoxide ("CO") Sensors in Carpark Fans

Why?

§  short payback period
§  easy to retrofit in an existing system

Where do they work best?

Office Buildings (Types 1, 2 & 3)

Hotel Buildings

Image Source: Cool Automation

Overview

Air pollutant levels in carparks typically peak at morning, lunch and after-work hours. However, carpark extraction fans often run continuously or on fixed schedules to maintain safe CO levels. Installing CO monitors and controls can provide a demand-based operation to switch off or slow down the fans during non-peak periods. VSD controllers can also be added to existing fans to improve energy performances in low-demand scenarios.

CO sensors can not only reduce electricity consumption, but also extend the lifetime of the fans.

Modelled Costs and Saving Potentials (assumptions are listed in Appendix A)

Carpark CO Sensors

Capital Cost (per m2 carpark area)

HK$90

Payback Period (years)

1.4

Saving Potentials (per m2 carpark area)

Cost

HK$66/year

Energy

59 kWh/year

Carbon

35 kg CO2-e/year

Advantages

  • short payback period
  • mature and reliable technology, so sensors can be easily retrofitted into existing systems
  • significant energy savings can be achieved, depending on size and operation of the carpark
  • reduced fan use, which increases fan lifetime and reduces maintenance costs 

Limitations

  • calibration and maintenance work will be required for optimal performance

Additional Considerations

  • carpark air quality standards need to be monitored to ensure a safe operation and fulfil Transport Department requirements
  • need to ensure that the smoke extraction system will not be affected

Relevance to Landlords and Tenants

  • both installation costs and cost savings will be on the landlord-side

 

 

 

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