Hi HVAC Efficiency: 3 Part Series: Part 1: Innovations Offer Reductions In HVAC Energy Consumption But Are Often Ignored.

Hi HVAC Efficiency: 3 Part Series: Part 1: Innovations Offer Reductions In HVAC Energy Consumption But Are Often Ignored.

In recent years, the industry has devoted a great deal of effort to reducing the amount of energy used to operate buildings. During that time, a variety of innovative HVAC technologies and design strategies have been developed and proved in a wide range of projects. Those approaches, however, are often ignored when HVAC options are being weighed. That's unfortunate: Wider use of those HVAC strategies represents a substantial opportunity to cut energy consumption, since more than one third of the energy used in a building is for heating, cooling, and ventilation.

Those strategies are also crucial for projects aiming to achieve net-zero energy use. A net-zero energy (NZE) building is one where the total energy consumed over a period of one year, minus renewable energy generated on-site, is equal to or less than zero.

Designing a very efficient HVAC system, whether it's for a net-zero building or not, can be a significant task, and it is best accomplished through an integrated, holistic design approach. This approach requires the commitment and contribution of owners, architects, engineers, contractors, and other specialists. Building owners and facility managers play an integral part even beyond the design stage: Even the best-designed projects rely on the user's motivation to operate the building with a high level of energy efficiency — especially when striving for net-zero energy.

The appropriate selection of HVAC systems offers many opportunities to achieve great efficiency. But the first step in designing an efficient HVAC system, regardless of whether the project's goal is to achieve net-zero energy use, is to cut the demand for energy. This is accomplished by reducing building internal loads, by improving building envelope performance to reduce solar heat gains and conductive losses, and, at the same time, by maximizing the use of daylight.

Depending on the climate, cooling demand can be reduced by increasing building insulation and installing high-performance glass. Light-colored, reflective surfaces on roofs and walls and radiant barriers within ceilings are also important to avert solar radiation.

In recent years, there have been developments in dynamic building envelope technology that can alter performance in order to withstand peak periods. Smart glass or self-tinting products are controlled based on an electric signal. Phase-change materials can be installed in drywall in order to maintain surface temperatures during extended hot periods.

Internal electrical loads for lighting and power systems should also be reduced as much as possible to increase efficiency. About 39 percent of building energy use goes to lighting and office equipment. Reducing internal electrical loads also cuts the demand for cooling: For each kW consumed, a percentage of waste heat must be cooled.

PART 2: Consider These Passive Or 

Energy-Efficient Active HVAC Systems:

Once heat gain is reduced, passive HVAC systems or more energy-efficient active systems can be installed to satisfy occupant comfort.

Passive systems are effective in net-zero buildings because they allow the user to maintain comfort in a space without the need for energy. Common passive techniques include natural ventilation and the use of thermal mass.

Natural ventilation relies on outdoor air and appropriate high/low window placement to ventilate, bring in fresh air, and relieve hot air. Exposed thermal mass can often be provided in the form of concrete, water, or other materials to evenly regulate surface temperatures, even when exposed to heat. Exposed thermal mass is often used in conjunction with natural ventilation in order to pre-cool surfaces at night and store this coolth for daytime use.

Passive systems have two limitations: They can be slow to respond to changes in load, and they can have limited capacity. This makes the load-reduction strategies even more important. In mixed-mode buildings, passive systems are supplemented by active HVAC systems to operate during periods when outdoor temperatures are high or low.

Energy-Efficient Active Systems:

When it comes to active-system design strategies, it's important to remember that any measures that can help occupants maintain comfort without turning on building HVAC systems should be considered. Local personal workstation cooling systems or high-volume, low-velocity ceiling fans may allow facility staff to increase building temperature set-points while maintaining comfort. The premise of "adaptive comfort" is that people can accept a wider range of temperature if they have the means to make adaptive, local adjustments such as altering air velocity, modifying clothing levels, or changing the activity schedule.

For heating applications on small- to mid-sized commercial net-zero projects, electric heat pumps are often the preferred means for generating heat. The reason is that they can take advantage of electricity from on site renewable sources (e.g., from photovoltaics or wind turbines); that's why net-zero projects use natural gas heating systems less often than other types of projects. Other sources of heat, such as solar thermal collectors, are common ways to offset the electrical heating requirements.

Radiant systems, such as chilled or heated floors and ceilings, are effective for net-zero applications both in heating and cooling. These systems temper the environment without needing a fan to circulate air. Air-plus-water systems, such as active chilled beams, can also offset fan energy. A pump is required to circulate water; however, water is a much more efficient medium for transferring heat or cold than air.

For applications requiring large quantities of air, either due to ventilation or cooling demand, a means to offset fan energy should be considered.

The conventional method for doing this is to reduce supply air volume during temperate periods using a variable air volume (VAV) system. A VAV system uses a variable frequency drive in conjunction with the fan to modulate speed. Because fan power depends on airflow and static pressure, some systems look to save energy by reducing static pressure. An underfloor air distribution (UFAD) system can accomplish this goal by moving low-velocity air through a raised floor cavity to reduce the length of high-velocity air ducts. A UFAD system also supplies air at a higher temperature than VAV systems and often uses outside air to provide free cooling, leading to greater efficiency.

For larger applications, central plants employ water-cooled chillers with heat rejection from cooling towers. For this size of net-zero project, efficiency would be the driver for all mechanical components. There are opportunities, however, to use natural energy sources such as geothermal heating/cooling to modulate temperature in the HVAC fluids.

PART 3: Net-Zero Energy Buildings: Waste Heat Recovery And Renewable Energy:

Waste heat recovery and renewable energy are important strategies in net-zero energy buildings.

Because natural gas systems are less often used in net-zero buildings, there are fewer opportunities to recover energy from the heat-intensive processes. If natural gas is not used for heating, a project is unlikely to use fuel cells or micro-turbines, eliminating the ability to recover waste heat from those energy-generating systems.

On many projects, waste heat sources occur within the exhaust air streams or in condenser exhaust from heat pumps or chillers. Depending on the use of the incoming air and the quality of the outgoing air, heat can be transferred using air-to-air heat exchangers, air-handling-unit run-around coils, and thermal energy wheels. These systems either directly or indirectly transfer heat from one air stream to the next.

Another source of waste heat is the exhaust air from heat pumps or condenser water from chillers. If there is a simultaneous demand for heating (possibly in domestic hot water), this waste energy can be reused as a heat source.

Renewable Energy and Building Automation:

The steps outlined are important in another way for projects aiming to achieve net-zero energy use. Those projects decide which renewable power generation system (photovoltaic cells, building-integrated wind turbines, bio-fuel, or some other means) best matches the building demand and profile for the project type and region. Measures that reduce demand also help to reduce first cost of the generation system, and make it easier to deal with the source's intermittent power production. The protocol we've outlined makes it easier to size energy-generating systems at an appropriate and affordable capacity.

Building occupants also play an integral role in efforts to achieve energy efficiency, especially in net-zero buildings. If the user is unaware of the energy consumption in relation to the building energy generation, there is little chance of achieving a neutral energy balance (i.e., net-zero energy use) at the end of the measurement period. Building dashboards allow the user to monitor building energy consumption and to better understand when manual systems should be operated. For instance, the building dashboard may notify the user when outdoor air temperatures are acceptable for opening a window or inform the user when energy conservation may be needed on a cloudy day.

The design of a highly efficient HVAC system, especially for a net-zero project, is a complicated puzzle that requires all members of a project team to engage in the process. More than ever, there is reliance on all members to cooperate, motivate, and inspire their counterparts to achieve the common goal of energy neutrality. The reward is a net-zero building that can meet the needs of the present while having "zero" impact on the ability of future generations to meet their own needs.

Bruce McKinlay, PE, LEED AP, is a principal with Arup in Los Angeles and leads the firm's commercial property market in the Americas. He has collaborated on numerous sustainable projects where an integrated design approach has led to greater energy efficiency. He can be reached by email by clicking the following link here.

Jamey Lyzun, PE, LEED AP, is an associate at Arup and has 14 years of experience on projects. He has applied many of the techniques outlined in this article to assure that integrated strategies at the design phase can lead to low energy and sustainable outcomes during operation. He can be reached by email by clicking the following link here.

Hi Earth tunnel Air conditioning!.

Hi Earth tunnel Air conditioning!.

Earth tunnel Air conditioning system also known as passive air conditioning, is a wonder utilization of nature. It is also called as Earth tubes in Europe, Earth-air heat exchangers in North America, Earth tunnelling in India. These systems are known by several other names, including air-to-soil heat exchanger, earth channels, earth canals, earth-air tunnel systems, ground tube heat exchanger, subsoil heat exchangers, underground air pipes, and others.

Material;

Most systems are usually a network of pipes made of concrete, PVC, steel, rigid or semi-rigid plastic, plastic-coated metal pipes or plastic pipes coated with inner antimicrobial layers. These pipes are 100 – 600 mm (4 - 24 inches) in diameter and have a smooth inner surface. The diameter, layout and cleanliness of the piping is critical for the overall performance of the system.

Smaller diameter tubes require more energy to move the air and have less earth contact surface area. Larger tubes permit a slower airflow, which also yields more efficient energy transfer and permits much higher volumes to be transferred, permitting more air exchanges in a shorter time period.

Laying;

Soil temperature, at a depth of about 4.0 to 5.0m (12 - 15 feet), stays fairly constant throughout the year, and is approximately equal to the average annual ambient air temperature. Ground temperature becomes more stable with depth. The ground can, therefore, be used as a heat sink for cooling in the summer and as a heat source for heating in the winter.

The underground ambient earth temperature is typically 10 to 23 °C (50 -73 °F ) all year round in the temperate latitudes where most humans live. Daily and annual temperature fluctuations decreases with the increase in depth below the ground surface.

Daily temperature variations hardly affect the earth's temperature at a depth of more than one meter, while the seasonal variations of the ambient temperature are strongly dampened by the earth. The earth's temperature up to a depth of 6.0 to 8.0 m (18 – 24 feet) is influenced by the annual ambient temperature variations with a time delay of several months.

Avoid;

The piping system should avoid sharp 90-degree angles in the construction. Smooth wall tubes are more efficient in moving the air, they are less efficient in transferring energy. Two 45-degree bends produce less-turbulent, but more efficient air flow.

Types;

1. Closed loop system : In this system, same air is recirculated in the building. The air from inside the building is blown through a U-shaped loop of pipes which are 30.0 to 150.0 m (100 to 500 feet) in length. The air is moderated to near earth temperature before returning to be distributed via ductwork throughout the building. The closed loop system can be more effective than an open system, since it cools and re cools the same air.

2. Open system : In this system the outside air is drawn from a filtered air intake. The cooling tubes are typically 30.0 m (100 feet) long straight tubes drawn into the building. It is a process of exchanging the energy contained from outdoor ventilation. During the warmer seasons, the system pre-cools and dehumidifies, while humidifying and pre-heating in the cooler seasons. This system helps to improve the indoor air quality while reducing total HVAC equipment capacity.
   An open system combined with energy recovery ventilation can be nearly as efficient (80-95%) as a closed loop, and ensures that entering fresh air is filtered and tempered.
   
   
3. Combination system: This is a combination of both the above systems. This can be constructed with dampers that allow either closed or open operation, depending on fresh air ventilation requirements. Such a design, even in closed loop mode, could draw a quantity of fresh air when an air pressure drop is created. It is better to draw in filtered passive cooling tube air than unconditioned outside air.

Working;

A tunnel is dug 4m below ground level and network of pipes are laid. The length of the pipe is proportional to the area of the building that has to be air conditioned. One of the above system is used to circulate or recirculate the air. Fresh air which is drawn from inside or outside the building, is forced into these pipes which passes through the cooler or heater where the air is cooled or heated and it then pumped into the building. This method helps air to pass through an underground air tunnel. The air thus cooled or heated can be used directly for the conditioned space or indirectly with air conditioners or heat pumps.

The ambient air ventilated through this tunnel will get cooled in summer and warmed in winter. This method can be used for cooling in summer and heating in winter. This method can be used for either partial or full cooling and/or heating of air.

Removing hot air from building

The simple method called as Stack effect system connects the vertical ducts that project above the roof line of the building and works using the convection system of air by sucking out the stale air. The roof is fitted with a fan which takes away the hot air from the vertical pipes.

Maintaining moderate earth temperature

Sensible cooling can be aided by evaporative cooling. To reduce the underground temperature, the ground can be shaded using vegetation and can be wetted by sprinkling water. This water seeps through and dampens the tunnel walls. A slow drip watering system may improve thermal performance. Damp soil in contact with the cooling tube conducts heat more efficiently than dry soil.

Merits;

• better indoor air quality.
• 100% fresh air circulation in the premises.
• cost effective in both up-front and capital costs.
• reduces long-term operation and maintenance costs
• consumes 1/3 Rd less energy than conventional AC system.
• minimum temperature can be achieved during peak summer.

Demerits;

• performance of the system depends on location's latitude, altitude, ambient Earth temperature, climatic temperature, relative humidity extremes, solar radiation, water table, soil type, soil moisture content and the efficiency of the building's exterior envelope design.

• dry and low density soil with little or no ground shade will yield the least benefit.

• less effective in hot humid climates where the ambient temperature of the earth approaches human comfort temperature. The higher the ambient temperature of the earth, the less effective they are for cooling and dehumidification.

Environmental impact;

With reference to today's diminishing fossil fuel reserves, increasing electrical costs, air pollution and global warming, properly designed earth cooling tubes offer a sustainable alternative to reduce or eliminate the need for conventional compressor-based air conditioning systems. They also provide the added benefit of controlled, filtered, temperate fresh air intake, which is especially valuable in tight, well-weathered, efficient building envelopes.

Hi Artificial Cooling Tricky Topic for Climate Panel!.

Hi Artificial Cooling Tricky Topic for Climate Panel!.

BERLIN (AP) -- It's Plan B in the fight against climate change: cooling the planet by sucking heat-trapping CO2 from the air or reflecting sunlight back into space.

Called geoengineering, it's considered mad science by opponents.

Supporters say it would be foolish to ignore it, since plan A - slashing carbon emissions from fossil fuels - is moving so slowly.

The U.N.'s expert panel on climate change is under pressure from both sides this week as it considers whether geoengineering should be part of the tool-kit that governments use to keep global warming in check.

Russia, in particular, has been pushing the panel to place more emphasis on such techniques in a key document for policymakers being finalized in Berlin this week.

Drafts leaked before the conference only mentioned one of the options, removing CO2 from the air and storing it underground. Russia, a major oil and gas producer, said the Intergovernmental Panel on Climate Change should also mention solar radiation management, which could include everything from covering open surfaces with reflective materials or placing sun-mirrors in orbit around the Earth.

'It is expedient to give a short description of the approach and mention the major 'pro and contra',' Russia said in comments submitted to the IPCC and seen by The Associated Press.

But even advocates of studying geoengineering express doubts.

'Really at the present moment there is a high level of uncertainty surrounding all of these options,' said Steve Rayner, co-director of Oxford University's geoengineering program. Still, he said it's worth continuing to research geoengineering 'to get a better sense of whether there's any merit in pursuing these technologies further.'

After discussions among governments and scientists, a mention of geoengineering was added last year to the first of four summaries of the IPCC's authoritative assessment on climate change. They are now working on the third one, which deals specifically with fighting climate change.

The document is important because it will be used as scientific guidance for governments as they negotiate a new global climate pact, set to be adopted in 2015.

Some environmental activists watching the talks in Berlin want the Intergovernmental Panel on Climate Change to scratch references to geoengineering altogether. They worry that such technologies would be ineffective, possibly harmful and delay efforts to shift the world's energy system from oil and coal to low-carbon energy sources like wind and solar power.

'It seems like a dangerous gamble to hold up this technology that may not work,' said Jim Thomas, of the Canada-based ETC Group.

However, the IPCC's draft document says that unless emissions are cut much faster than currently projected, measures to scrub CO2 from the air will be have to be deployed to avoid potentially dangerous levels of warming.

The problem is those technologies don't exist yet or are in an experimental stage. 

- "No one knows whether they will be successful."

Ideas include spraying clouds with seawater to make them more reflective or pumping aerosols into the air to mimic the cooling effect from major volcanic eruptions.

Each is associated with unknown risks, including potentially shifting weather patterns or damaging the ozone layer that protects the Earth from ultraviolet sunrays.

One technology that is currently being tested at a small scale is called 'bioenergy with carbon capture and storage,' or BECCS. 

The idea is to grow crops that absorb CO2 from the atmosphere then burn them in a power station to generate energy. 

The resulting CO2 emissions are captured at the plant and then stored deep underground. The net effect of that process is that CO2 is removed from the air.

In a scientific report underlying the summary for policy-makers being discussed in Berlin and obtained by AP, the IPCC notes that BECCS could play a key role in curbing the buildup of CO2 in the atmosphere, which scientists say is the main reason for global warming. 

However, it would have to be deployed at a large scale, which would require major investments. 

There could also be negative impacts if food crops are replaced by bio-crops.

Right now the carbon removed through this technique is only a fraction of the 30 billion tons of CO2 emitted annually from the combustion of fossil fuels.

'BECCS faces large challenges in financing and currently no such plants have been built and tested at scale,' the IPCC says in the draft report.

Hi Sustainable Development in Industrial Ventilation

Sustainable Development in Industrial Ventilation

The best route to sustainable development in industrial ventilation, dust extraction and waste extraction is through the design of the system. Moving air requires energy. Heating air requires energy. In both cases the potential to save energy over a prolonged period through good design exceeds that from other current efficiency developments. Key points of design include:

• The air volume
• Fan efficiency and motor control
• Heat recovery and air make-up
• Training and maintenance

Air volume:

The broad spectrum of industrial ventilation and process extraction requirements means that a simple solution to sustainable development is not possible as, for the most part, each system is a bespoke design for the specific application. However, optimizing the air volume in each design is without doubt one of the best. Why?

• Air volume is directly proportional to power
• 10% less air means 10% less energy

How is this achieved? Often through the design of the hood, the position relative to the emission source and how much that source is enclosed.

The hood designs in the diagram above represent concepts as there will often be limitations on how far this design philosophy can be followed. However, it is clear to see that the position of the hood relative to the emission source and changing to an enclosure hood design, where practicable, could reduce the required extraction air volume significantly.

Fan efficiency:

The range of fans used across the application of ventilation and process extraction systems being typically considered could have efficiency from 50% to 80%. The fan efficiency compares the input energy to the work done and has a significant impact on energy consumption, for example,

• 40,000 hours operation broadly equates to 5-years @ 24/7 or 10-years @ 16 hours 5 days per week.

Based on 25kW aerodynamic energy requirement and an energy cost of 10p/kWh

• A 50% efficiency fan would consume 50kW/h, at a cost of £200,000.00
• A 75% efficiency fan would consume 33.3kW/h, at a cost of £133,200.00

If this is compared to the stated difference in efficiency between IE3, IE2 and IE1 motors of around 1.5-2%, at these motor ratings, then notwithstanding the possibly increased capital cost of selecting a higher efficiency fan, the energy savings through the 40,000 hour life cycle are vastly more significant than the initial costs. For more information on these motor standards, look up "Premium efficiency" on Wikipedia.

Motor control:

A related aspect to consider is the motor control where further energy saving possibilities exists although often not through the widely promoted speed or frequency inverter control.

In the first instance it is necessary to appreciate the laws of physics which apply to fans once installed in a system, assuming there are no changes to the ducting design.

• A 10% increase in the fan speed increases the volumetric airflow by 10%; however it requires a 33% increase in electrical power.
• Conversely, a 10% reduction in the fan speed reduces the airflow by 10% and reduces the electrical power by 27%. Just 5% speed reduction reduces the power by 14% so the savings through speed optimization can be significant.

However, a fan only absorbs the power required to do the work so, reducing the speed by 10% through a change in the drive belts may provide the saving at a modest investment. And as the power and motor size increase the savings become disproportionately greater.

% fan speed	80%	90%	100%	110%
% motor load kW	51%	73%	100%	133%

Table of motor power change with fan speed change

Example

• 37kW motor installed
• 32kW absorbed by the fan
• Energy cost per annum, 24/7 operation, is £27,955 @ 10p/kWh.
• Energy cost per annum, 16/5 operation, is £13,312
• 10% speed reduction means absorbed power becomes 24kW
• Assuming new drive belts and labour costs £500 (renewed annually anyway)
• Then first year net saving at 24/7 operation is circa £7,000, then £7,500
• And first year saving at 16/5 operation is circa £3,000, then £3,500.

Of course this is only applicable to a fan with a drive belt system fitted. An inverter controller will do the same, although the installation would cost more and an older motor may not be suitable for frequency variation control.

It should be noted there are certain advantages in using an inverter over the simple drive belt option including:

• Applicable to all fans; direct drive or belt drive
• Further speed change adjustments are easily made
• Little loss in motor efficiency at reduced speeds, whereas reduced power at unchanged motor speeds may reduce the motor efficiency
• Fan speed reduction is limited to reducing the rated motor power by 50%, when other factors may come into play
• Applications with frequent start/stop cycles

In designing an extraction system, it is prudent and not untypical to err on the side of caution and allow for a modest increase in airflow and hence fan speed on completion of the installation, which would have an impact on the power required, and to select a motor one size above the bare minimum required. However, once installed and commissioned at the correct speed, the load on the motor may be some way below the motor duty, although only drawing the proportionate electrical current. Often a case is made for inverters based on the installed power rather than absorbed power of the fan motor. It is fairly simple for an electrical engineer to measure the running current of the motor compared to the motor rated full load current (FLC) to provide an indication of the energy being used.

Air input:

Exhausted air must be replenished either uncontrolled through egress into the building or controlled through an air make-up supply. Whenever the external temperature is below the required internal level, heat energy will also be required. Whether or not the air entering is controlled or not is often dependant on the building size and relative amount of extracted air. As an example, 70kW of heat energy would be required for a 20OC temperature rise in 10,000m3/h and with a 5p/kWh heat energy, could cost around £10,000 per annum on a 24/7 operation.

More sustainable approaches to air make-up include controlled introduction which reduces draughts and may, in some instances, lessen the heat load required. Re-using exhausted and filtered air will have an operational cost however often shows a payback within two to three years. Although less efficient than returning filtered air, heat exchangers may also enable the re-use of exhausted heat energy when filtering in impracticable. Sources of "free" heat should also be considered, compressors and hot process areas being valuable sources on occasion.

Once into operation the levels of training and maintenance can have an impact on wasted energy, environmental emissions or waste materials requiring landfill disposal.

The main objective under these headings is achieving optimum performance. By definition energy, emissions and waste are then controlled. It is a difficult position to reach and maintain. As ventilation and process extraction, (dust or waste), provide secondary or support roles to the principle production process all too often they get a lesser level of training and maintenance. Performance may decline gradually over time and often goes unnoticed with some examples including:

• Incorrect low compressed air pressure or cleaning control settings resulting in lower filter cleaning efficiency. This increases pressure drop and hence the absorbed motor power, and may reduce extraction efficiency.
• Incorrect high compressed air pressure resulting in "puffing"- dust passing through the filter bags due to over-cleaning which increases the carry-over emissions and reduces the life of the filter bags through fatigue during the cleaning process.
• Incorrect fan belt drive adjustment leading to a loss of fan speed which could lead to lost production through a build-up in the ducting or lower efficiency in the extraction and a reduction in the control measure. Complying with COSHH/LEV guidelines may help to identify this, however with 14 month intervals there is a risk of long term deficiency.
• Operators using equipment in an unintended manner is all too frequent and often goes unrecognised. When this situation occurs, performance as a control measure, emissions to atmosphere and an increase in energy consumption may easily result.

In conclusion, sustainable developments in industrial ventilation and process extraction applications are not only achievable but may be quite significant because they are based on good system understanding, design and use. Interestingly many recent developments in energy efficiency are over shadowed by the improvements which may be possible through design, equipment selection and an on-going user training and maintenance programme. It is clear that any low cost installation advantage may be far from the lowest overall cost and soon offset as running and service costs are included over a modest period of time. Also, when using and maintaining the system as intended, the safety and protection provided will be optimised.