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4-pipe FCUs have dedicated coils for heating and cooling and thus four pipe connections (hot and cold flow and returns).

Limitations:

Four-pipe FCU systems are more complex and have higher installation costs compared to two-pipe or three-pipe systems. Four-pipe FCUs require more physical space due to the separate heating and cooling coils. Four-pipe FCU systems may consume more energy than simpler systems. Running both heating and cooling simultaneously can be inefficient and result in wasted energy.

Case Study:

Caice 4-Pipe Fan Coil Units for new global headquarters for Booking.com in Manchester.

https://caice.co.uk/portfolio/4-pipe-fan-coil-units-manchester/

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FCUs that use refrigerant will often have 3-pipe connections (hot and cold flow and a single return) allowing for simultaneous heating and cooling to separate zones. Some systems achieve simultaneous heating and cooling with only 2-pipes (flow and return) where the flow pipe contains refrigerant in both vapour (for heating) and liquid (for cooling) form.

Limitations:

Three-pipe FCUs typically involve higher initial installation costs due to the complexity of the system. They operate with a constant flow of refrigerant which can lead to cooling or heating occurring simultaneously, reducing overall efficiency. The additional piping and components required for a three-pipe system may demand more space than a two-pipe system. There is a health and safety risk involved with these systems due to the use of refrigerants.

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2-pipe FCUs have only one coil so they can only provide heating or cooling at any one time. Their mode can be changed on a seasonal basis as required.

Limitations:

Two-pipe FCUs are designed for either heating or cooling at a given time, not both simultaneously and this is inefficient in spaces that require quick changes from cooling to heating. Only heating or cooling at one time can result in energy waste and discomfort during seasonal transitions. The installation and maintenance of two-pipe FCU systems can be more complex than other systems as they need separate heating and cooling coils and control valves.

Case Study:

UCD University Club - Entropic Limited

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Waterside Control FCU's use water as the heat transfer medium for both heating and cooling. They utilise a valve to control the flow of water through a small clearance section within the valve.

Limitations:

Waterside control systems involve the circulation of water, and the risk of water leaks is a concern - needs to be maintained to prevent leaks which will result in water damage and potential mold issues. Waterside control FCUs require space for the installation of pumps, valves, and associated equipment, which can be challenging in buildings with limited space. They are also dependant on the performance of the chiller or boiler in the central plant.

Case Study:

Embassy Gardens, Ballymore - Fan Coil Units

https://www.dimplex.co.uk/sites/default/files/2023-02/GDHV%20-%20Ability%20Case%20Study%20-%20Embassy%20Gardens%20-%20220422%20-%20V2.0.pdf

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A fan coil unit is a relatively small piece of equipment that consists of a fan, a coil, and other components, that are used to cool or heat the air recirculating within a room.

FAN COIL UNITS | What, Where & How - Constructandcommission.com

Limitations:

FCUs may struggle to maintain precise temperature control, especially in large or open spaces. Their on/off cycling can lead to temperature fluctuations and discomfort for occupants. FCUs may struggle to maintain precise temperature control, especially in large or open spaces. Their on/off cycling can lead to temperature fluctuations and discomfort for occupants. FCU's can generate noise from the fan motor and can be quite disruptive. FCUs primarily focus on heating and cooling, and may not provide adequate ventilation - a separate ventilation system may be required.

Case Study:

Iveagh Garden Hotel - Fan Coil Units - Entropic Limited

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A fan blows air across a heat exchanger coil that will contain hot or cold water (or refrigerant for VRF/VRV systems).

Limitations:

Airside control fan coil units can produce noise, as they use fans for air distribution. Airside control systems can, in some instances, be unsuitable in certain applications due to physical space restrictions.

Case Study:

University of Sheffield Advanced Manufacturing Research Centre with Boeing

https://caice.co.uk/portfolio/university-sheffield-advanced-manufacturing-research-centre-boeing/

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Air is supplied from the AHU at a constant temperature to a number of VAV units, each with a damper which controls the flow of air through it depending on the cooling or heating loads.

Limitations:

VAV systems can be more expensive to install than constant volume systems. VAV systems can lead to increased air velocity and turbulence, resulting in high noise levels. The installation and set up is considered difficult and complex.

Case Study:

TEL_Thermo_Fisher_Scientific_CaseStudy_2.pdf (tel-uk.com)

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The system is split into an outdoor heat rejection unit and an indoor room cooling unit. The refrigerant is pumped directly between the units and operates with 2-pipe connections.

Limitations:

Indoor units of split systems can produce noise, which may be a concern for some users. They are not suitable for cooling or heating large spaces or entire buildings, they suit small areas or individual rooms. The indoor unit of the split system is visible and can be considered unappealing in spaces where aesthetics are important.

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Warm water is piped across fans within the dry air coolers forcing the temperature of the water to drop.

Limitations:

Dry air coolers typically have lower cooling capacity compared to water-based systems. Dry air coolers are less effective at very high ambient temperatures. Dry air coolers typically require more space than water-based cooling systems, as they need ample space for air circulation. Operational costs can be quite high due to the electricity required to run the large fans.

Case Study:

Large project requiring 37 x Dry Air Coolers for a Facilities management building in Sunderland

Facilities Management Building, North East - Coolers & Condensers

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A cooling tower is more efficient than a dry air cooler because it uses evaporated water to assist the rejection of unwanted heat but requires greater maintenance.

Limitations:

Cooling towers require a constant supply of water which may affect water-scarce regions and add to water treatment costs. The evaporation process in cooling towers can lead to the release of water vapor containing water treatment chemicals, which can have environmental impacts. Cooling towers are susceptible to corrosion and scale formation, which can reduce their efficiency and lead to equipment damage.

Case Study:

Atlantis Plastics Company in Houston

Cooling Tower Efficiency Boosts Bottom Line for Plastics Manufacturer | Delta Cooling Towers, Inc.

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Chilled water is produced via a centralised plant and then circulated to services throughout the building.

Limitations:

Chilled water systems are expensive to install and the initial investment can be a significant barrier for some applications. They have a high operation cost due to the electricity required to run them. Chilled water systems also require a constant supply of water which has to monitored to prevent scaling, fouling or biological growth.

Case Study:

Chilled Water System for the Eiteljorg Museum in Indianapolis

Paper Title (use style: paper title) (energy-proceedings.org)

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Plant equipment to produce chilled water. Heat is removed from an unwanted area and rejected externally. Packaged chillers include heat rejection as part of the unit. Other chillers require dedicated heat rejection plants, such as dry air coolers and cooling towers.

Limitations:

Chillers consume a significant amount of electricity, which can lead to high operating costs.Chillers require regular maintenance to ensure proper operation. Neglecting maintenance can lead to reduced efficiency, increased energy consumption, and system breakdowns. When operating at partial load, such as during off-peak cooling demand, the efficiency can decrease, leading to wasted energy. Chillers also require a lot of space for installation.

Case Study:

CIBSE Case Study: TurboChill chiller | CIBSE

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AHUs maintain adequate ventilation by providing fresh, filtered outside air and delivering it at the condition required to the internal space. AHUs can be used to control the temperature and humidity of the air.

Limitations:

AHUs require dedicated space for installation, which can be a limitation in buildings with limited space. They also have high installation costs. he operation of fans and components in AHUs can generate noise and vibration, which can be a concern in certain environments.

Case Study:

Commercial Restaurant Air Handling Units | Ishbilia Case Study | Envirotec

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Variable Refrigerant Flow (VRF) and Variable Refrigeration Volume (VRV) systems circulate refrigerant like a split system but have multiple indoor units providing simultaneous heating and cooling. They can operate with a 2- or 3-pipe connection.

Limitations:

VRF systems typically have a higher upfront cost compared to traditional HVAC systems. A VRF system has many elements and components and this can make maintenance and servicing more challenging and potentially expensive. The refrigerants used in this system can cause harm to the environment if not handled properly. VRF systems may also have reduced heating capacity in very cold climates.

Case Study:

Variable Refrigerant Flow Applications & Case Studies | Educational Complexes | Albert Einstein Academy | San Diego, CA | Carrier Commercial Systems

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Active chilled beams operate in the same principle as the passive with the exception of having fresh air ducted to it. Rather than air being drawn into the beam by buoyancy it is induced by the ducted air.

Limitations:

Their cooling capacity can be limited especially in places with a high cooling load and so other cooling systems may be required to meet demands. Changes in humidity can affect the cooling performance and can cause condensation issues. Active Chilled Beams require regular maintenance.

Case Study:

Criminal Courts of Justice - Chilled Beams - Entropic Limited

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Long rectangular units located at high level circulate chilled water in finned pipes and exchange coolth. Convection occurs with warm rising air being cooled by the chilled beams.

Limitations:

They are only suitable for moderate cooling loads, they do not have the cooling capacity for high cooling demands. Passive chilled beams distribute air naturally through convection which can result in uneven cooling within a space.

Case Study:

Pharmaceutical Society Ireland - Chilled Beams - Entropic Limited

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These systems deliver a constant volume of conditioned air from the AHU. They are not suited to multi-zoned buildings with varying cooling requirements, therefore they are generally used in single zones, such as a central foyer or as part of a cooling system with the primary cooling being achieved by other means, such as FCUs.

Limitations:

CAV systems provide a fixed volume of conditioned air regardless of the cooling or heating demand in the space which results in energy waste and inefficient operation. Energy wastage can also been seen when this system works at part load as it is designed to work most efficiently at full load. Temperature control is often achieved by adjusting the supply air temperature and this can lead to temperature swings and inconsistent comfort levels in the occupied space.

Case Study

D5.1.3 - 2 Case Studies - cover.pdf (psu.edu)

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These utilise the heat from a CHP unit to generate chilled water by using an absorption chiller when cooling is required.

Limitations:

The installation and maintenance costs are quite high for a trigeneration system. This system is not free from environmental impact as it most commonly uses natural gas as a fuel which releases greenhouse gas emissions. Trigeneration systems are only really suitable and practical for industrial and commercial settings and not for smaller residential settings.

Case Study:

Australia’s Royal Children’s Hospital

Cogeneration examples across industries | Cummins Inc.

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These operate at atmospheric conditions without a fan or pressurisation and are one single unit. The air/fuel mix is controlled by gas flow drawing the air for combustion. Generally, atmospheric boilers will operate in either 'on/off' or 'high/low' settings and cannot modulate.

Limitations:

Atmospheric boilers are not very efficient when it comes to burning fuel, making it a serious drawback in terms of environmental pollution and household budgeting and the combustion chamber is not isolated from the room and this can expose toxic fumes to the residents of the home. Atmospheric boilers: Everything you need to know about these old favorites (suner.eu)

Case Study:

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Using a vapour compression cycle, a heat pump effectively takes ambient heat and converts it to a higher and more useful temperature. Heat pumps can be reversible to also provide cooling.

Limitations:

Heat pumps are often difficult to install with quite a significantly high installation cost. They have a higher electricity usage and can often be susceptible to power outages. Heat Pump Pros and Cons - What You Need to Know | HVAC Training Shop

Case Study:

Having a heat pump | Case Study | SEAI

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These use external ambient air as a heat absorption/rejection medium for the heat pump. They are cheaper and easier to install than some other heat pump systems but are subject to outside air temperature fluctuations and are vulnerable to possible physical damage.

Limitations:

Air Source Heat Pumps are expensive and laborious to install. They are also dependent on the outside air temperature and become less efficient when these temperatures fall. Air source heat pumps can struggle to maintain the same indoor temperatures if the external temperature is low. If working in low temperatures, they have to work harder and can often create a lot of noise. 11 Main Problems With Air Source Heat Pumps (Real Example) – Source Heat Pump

Case Study:

Robert and Maria's air source heat pump - Energy Saving Trust

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These use the ground as a heat absorption/rejection medium for the heat pump. Below ground temperatures are stable throughout the year so offer better efficiency than ASHPs. The disadvantages are the higher capital costs, the requirement for drilling boreholes for pipework and ground make-up on site.

Limitations:

Installing a ground source heat pump costs considerably more than air source heat pump installation due to the groundworks involved. This process is also quite disruptive to the home owners as digging is required. The installation of a GSHP also requires a large area of land and space which might not be available to people. Ground source heat pump disadvantages and problems | Ideal Home

Case Study:

Gwilym's experience with a ground source heat pump- Energy Saving Trust

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Combined heat and power (CHP)/ cogeneration

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Combined heat and power (CHP)/ cogeneration

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CHP units are effectively engines which convert the mechanical energy into electricity via a generator. The 'waste' heat produced by the engine is also utilised for heating and/or hot water, therefore increasing the energy utilised and efficiency of the system.

Limitations:

CHP or Cogeneration systems are often only suitable for buildings with a constant load requirement for space heating and hot water. The heat and water demand needs to remain constant for efficiency. CHP system is not seen as a true sustainable energy source as they use natural gas. Combined Heat & Power - advantages & disadvantages - helec

Case Study:

0057082.pdf (cummins.com)

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These consist of two main components; the boiler body and a burner. The burner contains a fan which forces the air to mix with the fuel giving more consistent mix ratios. Because the mix can be controlled, forced draught boilers can also be modulated.

Limitations:

The flue gases have to be discharged at high temperatures resulting in a loss to the overall plant efficiency resulting in maximum heat utilisation not being achieved. A forced draught boiler has high running and maintenance costs. 1627026603-boiler-types-draught-bbec.pdf

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These are considered a low-carbon alternative to conventional fuel boiler as it is fuelled by biomass (wood) or biodiesel. The variety of fuels and their respective calorific value can give varying outputs.

Limitations:

Biomass Boilers require a lot of maintenance due to the use of biomass to run them. They need to be regularly loaded with biomass fuel and cleaned out. They can also take up a lot of space as you also need to have space not only for the boiler itself but for storage of the wood as well. The price of wood can also fluctuate regularly so the cost to run may vary. Biomass Boilers (UK Guide) (energyguide.org.uk)

Case Study:

Tesco in Galway saw an Installation of 500kW Wood Chip Biomass Boiler - Enerpower

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Whereas a conventional chiller uses a compressor to raise the pressure (and temperature) of refrigerant in the refrigeration cycle, an absorption chiller uses heat (typically from a CHP system.

Limitations:

An absorption chiller has high initial costs and is also quite a bulky system which requires a lot of space.

Case Study:

Case study of the adsorption chiller driven by combined municipal heat and solar energy.

(PDF) Case study of the adsorption chiller driven by combined municipal heat and solar energy (researchgate.net)

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These are generally smaller in physical size and heat output than conventional boilers. Multiple modular boilers are usually coupled together to make up the total required duty allowing the boilers to fire separately giving greater flexibility and efficient performance. Other benefits include ease of installation, lower capital costs, reduced standby capacity requirement and space saving.

Limitations:

The initial installation cost can be more expensive than a traditional single boiler and can cause significant drawbacks for the owner. The installation is also more complex and time-consuming than a single-boiler system. Modular boilers can be more challenging to maintain because there are multiple boiler units to service and monitor.

Case Study:

Duke University Saves Energy with Miura Boilers - Miura America

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These can accommodate two fuels types, such as gas and oil.

Limitations:

Dual Fuel Boilers require regular maintenance to keep the system running smoothly. There is also a risk of potential hazards if your system uses combustible fuels like natural gas or propane if there is not adequate ventilation or safety plan in place. What is a Dual Fuel Heating System and Is It Right for You? - Trane®

Case Study:

Dual Fuel Wall-Fired Boiler | Dual fuel, coal and natural gas burners (stepcombustion.com)

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Condensing increases boiler efficiencies by removing heat energy usually wasted in the exhaust. Removing this energy causes the flue gases to condense resulting in water as a waste by-product.

Limitations:

There are several different limitations to condensing boilers. If the pressure of the hot water running through the boiler gets too low, the boiler can stop working. The condensate pipe becoming blocked or frozen is quite common and these systems are often susceptible to leaks or drips.What is a Condensing Boiler? | Boiler Guide

Case Study:

Case study: Specifying condensing boilers | Consulting - Specifying Engineer (csemag.com)