KJ Tait

As M&E consultants, the transition to decarbonised heating systems is a critical aspect of our work in the built environment.  One technology we often design is the 4-pipe heat pump system, which offers simultaneous heating and cooling capabilities. However, the implementation of these systems comes with several challenges that need to be carefully considered. 

Size and Installation Challenges 

4-pipe heat pumps are typically larger than traditional chillers, which can pose significant challenges when it comes to installation, particularly on rooftops. The structural integrity of the roof must be assessed to ensure it can support the additional weight.  This may require reinforcement, which can add to the overall cost and complexity of the project.  Additionally, the physical space available on the roof may be limited, necessitating creative solutions to fit the equipment without compromising other rooftop utilities.  The airflow requirements for these units are significant too, typically greater than for an air handling unit therefore must have unrestricted airflow. 

Electrical Capacity 

The electrical demand of 4-pipe heat pumps is another critical factor.  These systems require a substantial amount of power, which may exceed the existing electrical capacity of the building.  Upgrading the electrical infrastructure can be a significant undertaking, involving not only the installation of new wiring and switchgear but also potential upgrades to the building’s connection to the grid.  This can be both costly and time-consuming, and it is essential to conduct a thorough feasibility assessment to understand the full scope of the required upgrades.  For some buildings that are already cooled via chillers, the replacement of the chiller with a 4 pipe heat pump can be easier. 

Acoustics 

Noise is a common concern with heat pump systems, and 4-pipe configurations are no exception.  The operation of compressors and fans can generate significant noise, which can be disruptive to building occupants, particularly in residential or office environments.  Acoustic treatments, such as soundproof enclosures or barriers, may be necessary to mitigate this issue. Additionally, careful placement of the heat pump units can help minimise noise impact, but this must be balanced with other installation constraints. 

Retrofitting with Existing Heating Pipework 

One of the advantages of 4-pipe heat pumps is their ability to integrate with existing heating and cooling systems.  However, retrofitting these systems into older buildings can present challenges.  The existing pipework may not be compatible with the new system, requiring extensive modifications or replacements.  This can be particularly challenging in buildings with complex or pipework sized for high temperature. A detailed assessment of the existing infrastructure is essential to identify potential issues and develop a plan for integration. 

Where we have made a difference 

For one building in London, we have completed a feasibility whereby we are going to replace one of the chillers with a 4-pipe heat pump, however, just operate this in cooling mode at present.  We have taken this approach because this chiller is at the end of life.  If we replaced this like-for-like, it would be locking the building into a fan coil strategy. 

By replacing with a 4-pipe heat pump, it allows the building owner to consider longer term whether to replace the second chiller with a 4-pipe heat pump and retain the FCUs or to move to a VRF solution whereby the 4-pipe heat pump being installed would just supply the air handling unit. 

To arrive at this approach was an iterative process, it was the result of discussions with the onsite team and the building owner to understand current maintenance, HVAC plant life, budgets and tenant lease agreements expiry dates.  

Conclusion 

While 4-pipe heat pumps offer significant benefits in terms of energy efficiency and the ability to provide simultaneous heating and cooling, their implementation is not without challenges.  Careful consideration of the size and installation requirements, electrical capacity, acoustics, and compatibility with existing systems is essential to ensure a successful transition.  By addressing these challenges head-on, we can make significant strides towards decarbonising our heating systems and creating more sustainable built environments.