INTRODUCING MODULAIR- A COMPACT WATER CHILLER WITHOUT COMPROMISE!

ModulAIR is a water cooled chiller that brings robust serviceability and ASHRAE 90.1-2010 efficiency into a single compact package. Chiller sizes are available in 8, 10, 12, 15, 21, 25, 41, 48 and 55 tons. Each chiller can be used as a stand-alone unit or combined for installations up to 550 tons. Chiller modules of any size can be mix and matched without limitation!

Unparalleled serviceability

Some users try to avoid modular chillers because traditionally they haven’t been as reliable as conventional chillers. ModulAIR brings all the robust features of a full size chiller into a compact foot-print. Fully cleanable shell & tube condensers and replaceable filter driers mean that customers no longer need to sacrifice reliability when a compact design is needed. Standard features such as compressor oil level and flow monitors show that this chiller takes reliability more seriously than the rest.

Fg1.png

Unlike other modular chillers, ModulAIR is designed such that the condensers and evaporators can be serviced while the rest of the unit remains in operation. Unions on factory installed water piping can easily be removed to gain access to the front of the condensers for cleaning. The electrical control panels are hinged and rotate outwards allowing for easy access to the compressors. This means that service clearance is required from the front side of the chiller only, resulting in a smaller overall installation.

Smart control features

Smart controls are where this chiller differentiates itself from the rest. Each chiller module can run autonomously. The unique control algorithms are duplicated in each chiller module eliminating the need for any “master” controller. This removes a significant point of failure and improves redundancy for critical applications.

All ModulAIR chillers feature compressors with capacity control from 100% to 10% with advanced unloader technology. Operators no longer need to wonder at which point their chiller is the most efficient. The built in control sequence automatically determines how many compressors should be operational to deliver the lowest energy consumption possible. It doesn’t matter what the conditions might be, ModulAIR will automatically try different operational scenarios to determine which is the most efficient.

 

Fg2.png

For applications where down-time is not acceptable, ModulAIR features a unique high head pressure avoidance sequence. This means the chiller will anticipate a high head pressure lockout situation and make every attempt to remain online during the most harsh conditions. If a cooling tower fan motor fails, or condenser water flow is restricted, the chiller will unload its compressors to take advantage of whatever heat rejection capacity remains available. Conventional chillers will simply continue to control to their chilled water set-point and end up tripping on high head pressure, remaining offline until the facility operator hits the re-set button.

Energy saving options

A wide variety of feature are available on the ModulAIR chiller for users who are concerned with energy efficiency. For systems that require variable primary flow, chillers are available with 2-way motorized valves. This allows the chiller to control to a constant return temperature while saving on chilled water pump energy. The condenser features a water regulating valve to properly control head pressure while reducing the amount of condenser water required in winter months.

fg 3.png

Because of its modular design, other specialized accessory modules can be added to any system. A pre-engineered skid with pumps and tanks is available for a simplified installation. For water cooled systems, a free-cooling module is available which can take advantage of energy savings during winter months. This feature allows the chiller to save on compressor energy by using cold condenser water to cool the chilled water supply, rather than using mechanical cooling all year round.

ModulAIR can also help save energy in applications where cooling and heating is required at the same time. Condenser heat is wasted when it’s rejected outdoors. This can be used to satisfy heating requirements for domestic hot water, space heating, or other process heat loads. Unlike other small chillers that use high pressure refrigerants, ModulAIR uses a medium pressure refrigerant, allowing it to operate at higher discharge pressures more efficiently. This means that users can generate 175 F hot water from this chiller for all their hot water heating requirements!

For more information

ModulAIR is a compact water chiller manufactured by Advance Industrial Refrigeration (AIR). For more information, visit the ModulAIR page.

REFRIGERATION AS AIR-SIDE HEAT RECOVERY

Advancements in energy recovery technology have allowed for the drastic reduction in the amount of new heating energy required for ventilation air. Many forms of “passive” air-side energy recovery exist such as heat-pipes, enthalpy wheels, or air-to-air heat exchangers. While total effectiveness of these systems has increased to nearly 90%, their applications still remain limited by factors such as:

  • Contamination in the exhaust air which can damage the heat exchanger

  • Air leakage that can potentially recirculate hazardous air back into the supply air stream

  • Frost control that drastically reduces efficiency

These concerns have left behind a significant potential for further energy savings. Additionally, growing concerns about fossil fuels have put pressure on everyone to reduce natural gas use for heating, yet the cost for electric heat in most regions remains unreasonable.

The solution to these problems is found in the refrigeration cycle. Although the system is driven by an electric compressor, the efficiency gain far outweighs the additional electrical costs. A typical refrigeration system can achieve between 5 and 10 (COP) units of heat energy per unit of electrical energy. This means the operating cost is lower even when the price of gas is 5 to 10 times that of electricity.

 

f1.png

Figure 1

As Figure 1 shows, the compressor extracts heat from the evaporator (blue coil) in heating mode. The evaporator cools the air in the exhaust air stream and condenses moisture, allowing for both sensible and latent heat recovery. The compressor upgrades the heat to the required temperature and rejects it into the condenser (red coil). This achieves an “active” form of energy recovery that is able to meet the supply air temperature set-point without the need for additional sources of new energy.

With the design conditions shown, the outdoor air temperature is -4°F and the heating COP achieved is 5. What makes this heating system unique is the efficiency increases at part-load. This concept is similar to the “seasonal” efficiency achieved by conventional air-conditioners. When the outdoor air is 30 °F, the COP is nearly 8. By reducing the load, the suction pressure in the evaporator can be increased, reducing the lift on the compressor. Since the lift and load are reduced simultaneously, the situation also becomes ideal for using a variable speed compressor.

In the summer, the refrigeration cycle can be reversed such that it cools the supply air while rejecting heat to the return air. SInce the return air from the building is typically cooler than the design ambient temperature, the efficiency in cooling mode is also improved.

This type of system doesn’t come without challenges. The potential for the outdoor air temperature to fluctuate makes things difficult for the refrigeration system. In cold climates, frost control on the evaporator is also a concern. The successful implementation of this concept depends on many factors:

  • Having a robust compressor that can unload to nearly any condition

  • Using various devices to ensure proper operation throughout the refrigeration cycle

  • Implementing controls that can adjust operation to actively maintain head pressure and suction pressure

 

FG 2.jpg

Figure 2: FreshAIR, manufactured by Advance Industrial Refrigeration. 

You can get detailed product information from the ventilation section of our website. 

HEAT EXCHANGERS COMMONLY USED FOR EVAPORATORS AND CONDENSERS

The most common styles of evaporator and condenser heat exchanges used in Water Cooled DX and Water Chiller applications are Shell & Tube and Brazed plate. In the evaporator, refrigerant changes from the liquid to the gaseous state while removing heat from the cooling fluid. In the condenser, refrigerant changes from the vapor to the liquid state giving heat to the heat rejection fluid. Choosing the right heat exchanger depends on the situation at hand.

Brazed Plate Heat Exchangers

Their typical construction materials consist of stainless steel plates held together with a copper based brazing material. Water and refrigerant circulate in alternating plates. This style of heat exchanger can be used for both evaporators and condensers.

 

1-1024x768.jpg

Figure 1: Brazed plate heat exchanger installed in chiller as evaporator.

 Advantages:

  1. Their space efficient shape (rectangular allows for compact unit design.

  2. The non-ferrous construction eliminates rusting.

  3. The alternating plate design makes the brazed plate evaporators less susceptible to freeze damage when compared with shell and tube evaporators.

  4. The small passages encourage turbulent flow, which can benefit heat transfer.

  5. They are less expensive when compared with a shell & tube design.

Disadvantages:

  1. They cannot be serviced (cleaned, leaked repaired, etc.…)

  2. The smaller passages lead to a higher water side pressure drop.

  3. They are subject to plugging/fouling, also due to the smaller passages.

  4. Although they are typically constructed of stainless steel, the brazing material is copper based and can sacrificially corrode.

 

fig2.jpg

Figure 2: Passages on a brazed plate heat exchanger. Each passage is approximately 1/8” wide

Shell & Tube Heat Exchangers

Their construction materials usually consist of a carbon steel shell with end plates and copper tubes. With a DX Evaporator, water circulates in the shell side while the refrigerant passes through the inside of the tubes. In a condenser, the water flows through the tubes while the refrigerant remains inside the shell.

 

fig 3.jpg

Figure 3: Two shell & tube heat exchangers being used as condensers in a water chiller.

Advantages:

  1. Less water side pressure drop due to the larger tube size.

  2. Tube leaks are easily located and plugged.

  3. They can act as a liquid refrigerant receiver helping with pump-down and low ambient situations.

  4. Much easier to service (clean and repair leaks).

  5. A better solution for water derived from open cooling towers, rivers, lakes, sea coolant, and other fluids at risk of clogging in narrow spaces.

  6. Rugged mechanical construction due to its thicker tube walls.

  7. Tubes are available in a wide variety of construction types (Copper, Cupro-Nickel, Stainless steel, and Titanium)

  8. The shell is also available in stainless steel, for sea water and other highly corrosive applications.

 Disadvantages:

  1. Less thermally efficient due to less total surface area.

  2. Requires a larger space.

  3. More expensive when compared to brazed plate.

  4. In evaporators, the water is passing over a carbon steel surface.

  

fig 4.jpg

Figure 4: Shell & tube heat exchanger with end cap removed, tube passages are typically 3/4″.

Conclusion

For heat exchangers that use cooling tower water, river, lake or a similar source, it is highly recommended to use a Shell & Tube condenser because of its larger passages and lower probability of fouling and scaling. Shell & Tube heat exchangers can be easily cleaned just by removing the end plates and brushing the tubes. However, for situations that use a closed loop water source, or coolant such as glycol, a Brazed Plate condenser may be used to lower cost and achieve better thermal performance in compact design. When using a brazed plate heat exchanger, a strainer with an appropriate mesh size should always be used.

THE ECONOMICS OF HEAT RECOVERY SYSTEMS FOR WATER CHILLERS

Likely one of the most popular HVAC systems found in high rise residential, commercial, and industrial buildings is a chilled water system for cooling and a hot water system for heating. These systems are thought as two separate entities that operate independently. The issue with this philosophy is that for many hours of the year the chiller cools the process, rejecting waste heat outdoors, while the boiler consumes fuel to generate new heat. What does it take to turn this waste heat into something useful?

Theory

A typical situation is shown in Figure 1. Chilled water and hot water are produced simultaneously. These instances of simultaneous heating and cooling can arise from heating domestic hot water in the summer months, or in buildings that require cooling year-round. Let’s assume the simultaneous load is 1.0 Mbtu/hr of chilled water (83 tons) and 1.6 Mbtu/hr of hot water.

Figure-1-1024x646.png

 

Figure 1: Typical cooling and heating system.

The cooling system requires a chiller operating at 0.727 kw / ton and a cooling tower at 40.2 GPM / HP. For every 1.0 Mbtu of chilled water produced, the chiller and cooling tower consumes $7.27 and $0.55 of electricity respectively. A total cost of $7.82 / Mbtu’s of chilled water.

The heating system requires an 85% efficient boiler operating with natural gas generating 160 F hot water. The operational cost is $16.00 / 1.6 Mbtu’s of hot water.

The total cost to satisfy both loads simultaneously is $23.82 per hour of operation.

 

Figure-2-1024x807.png

Figure 2: Heat recovery operation.

With a heat recovery chiller as shown in Figure 2, the waste condenser heat is re-used to generate 160 F hot water. As a result, the chiller needs to work harder to produce the higher condenser water temperature and the electrical consumption of the compressor increases. The boiler and cooling tower are both off.

The total cost to satisfy both loads simultaneously is $19.40 per hour of operation. If we compare this to the situation in Figure 1, the operation cost savings are $4.42 per hour, or 23%. If we had a situation where this simultaneous load existed continuously, the annual savings would be $38,719.

Implementation
With the theoretical savings now understood, the question becomes how can this be implemented in a realistic situation. With the simultaneous load constant, the savings and pay-back can easily be calculated.

Figure-3-1024x830.png

 

Figure 3: Building heating / cooling load profile.
In Figure 3, the building has a cooling load profile shown by the blue curve. The load peaks in the summer time but some small amount of cooling is required through the winter months. We will assume this winter time minimum cooling load is 83 tons (1.0 Mbtu/hr). The building also has a heating load shown by the red curve. The heating load peaks in the winter but there is still some heating required in the summer (domestic hot water heating, for example). We will assume this minimum heating load is 1.6 Mbtu/hr. The area below both the red and the blue curves represent the total amount of energy available for heat recovery.

 

Figure-4.png

Figure 4: Effect of heat recovery on building load profile.

If we implement the heat recovery chiller previously discussed, the chiller will run continuously throughout the year, generating 83 tons of cooling and 1.6 Mbtu’s of heat. The reduction on the remaining cooling load is shown in Figure 4 with the green curve. This situation provides the maximum economic return when implementing heat recovery since the chiller operates continuously throughout the year.

Non-simultaneous loads

Summer Winter
Heating 0 to 1.6 Mbtu/hr (domestic hot water only) 6.0 Mbtu/hr (hot water and space heating)
Cooling 200 tons 83 tons

 

What if there is a situation where we cannot guarantee the need for heating and cooling at all times of the year? For example, a fluctuating domestic hot water load.  The table below gives an example situation of a summer and winter load for a building.

 

In the winter months, the cooling load is present and there is more than enough heating load to absorb the recovered heat energy. The issue becomes in the summer when the heating load fluctuates from 0 to 1.6 Mbtu/hr. If the hot water load is 0, there will be nowhere for the heat recovery chiller to reject its heat and it will not be able to produce cooling to satisfy the cooling load.

There are two potential solutions to this problem.

  1. Size a stand-alone heat recovery chiller to generate 1.6 Mbtu/hr of hot water and 83 tons of cooling. Install another 200 ton chiller. This will ensure that 200 tons is available even when there is no hot water demand. Although the building only requires 200 tons, the total amount of chiller installed becomes 283 tons.

  2. Size a heat recovery chiller to generate 1.6 Mbtu/hr of hot water and 83 tons of cooling with primary / secondary condensers. The primary condenser rejects heat to the cooling tower and the secondary condenser rejects heat to the heating loop. Install a 117 ton standard chiller. The total amount of chiller installed is 200 tons. See Figure 5.

 

Figure-5-1024x836.png

Figure 5: Heat recovery chiller with primary/secondary condensers.

The main benefit of option 2 is the cooling capacity from the heat recovery chiller can be included in the capacity of the entire chiller plant. This is because the heat recovery chiller will always be available regardless if heat recovery is needed or not. If there is no demand for hot water, the chiller can reject its heat to the cooling tower as needed. When the demand for hot water returns, the chiller with continue in heat recovery mode. With this solution, there is the obvious reduction in capital costs when considering a 200 ton plant versus a 283 ton plant. When installing a new chilled water system, the addition of heat recovery is simply the addition of a secondary condenser.

Other benefits

There are other side benefits of a heat recovery system.

  1. In systems where the space heating boiler is also responsible for domestic hot water heating, the boiler is typically oversized for domestic hot water heating. The boiler tends to cycle on/ off considerably through the summer months. The addition of the heat recovery chiller can greatly reduce this cycling, improve the precision of the hot water set point and increase boiler life.

  2. If the heating boiler is driven by natural gas or other fossil fuels, the addition of the heat recovery chiller will reduce the amount of CO2 emissions from the boiler.

  3. The reduction in cooling tower use will increase cooling tower life expectancy. When heat is recovered and not rejected to the cooling tower, less water will be consumed. The amount of chemical water treatment is also reduced.

Conclusion

Chiller heat recovery is an economically feasible solution that will produce significant operating cost reductions in a heating / cooling plant. As discussed, in a plant generating 160 F hot water and 44 F chilled water, the savings are 23%. If the building hot water temperature is lower – 140 F for example, the efficiency of the chiller is improved and the savings are even greater.

Utilizing a chiller with a secondary condenser gives flexibility in situations where heating and cooling are not always present at every moment of the year. This can help exploit situations where heat recovery was previously not economical such as, apparent buildings, schools, and smaller commercial spaces. When a new chilled water plant is being considered, the addition of heat recovery can simply be the addition of the secondary condenser, condenser pump, and associated water piping.  This helps keep capital costs low and improves the economic payback significantly.

For more information about heat recovery chillers and chillers featuring a secondary heat recovery condenser, visit the ModulAIR page.

 

IMG_1384-1024x768.jpg

Figure 6: Heat recovery chiller with primary/secondary condensers.

Assumptions

Chiller cooling efficiency: 0.727 kw / ton (44 F chilled water and 95 F leaving condenser water)

Chiller heat recovery efficiency: 1.94 kw/ton (44 F chilled water and 160 F leaving condenser water)

Boiler efficiency: 85% producing 160 F hot water

Electrical costs: $0.12 / kw-hr

Natural gas costs: $0.30 per m3

Cooling tower efficiency: ASHRAE 90.1 40.2 GPM / HP, or 0.055 kw / ton of cooling load.