Liquid-to-Liquid Heat Exchanger
Understand how the liquid-to-liquid heat exchanger works. Explore component overviews, measurements, and additional resources.
Overview
A liquid-to-liquid heat exchanger transfers heat between two liquids using a temperature difference without direct contact between them.
In a building, this type of heat exchanger can be installed in condensate cooling, vent condensing, boiler blowdown, and waterside economizer (free cooling), and in refrigeration applications such as evaporators and condensers. Typical liquid-to-liquid heat exchangers are plate and frame heat exchangers and tube heat exchangers and shell-and-tube heat exchangers.
How do I…
Quantify Electricity Usage (kWh)
The primary source of energy usage in a liquid-to-liquid heat exchanger is the dedicated heat recovery pump, if present. In some systems, the heat exchanger will have a dedicated pump that boosts the pressure differential at the exchanger. In other systems, the heat exchanger relies on the pumps that serve the respective distribution systems that it is attached to. In these cases, the energy is accounted for as part of those systems, not the heat exchanger.
Measure Motor Power Draw
Measure the heat recovery system pump motor (if present).
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure the hourly power draw of the pump (if present) and obtain the operating schedule of the pump.
Use this technique to measure outdoor air temperature if the system is weather dependent.
Assess Component Performance
The measurement strategy for a liquid-to-liquid heat exchanger involves measuring the supply stream flow through the heat exchanger and the temperatures at the supply stream inlet and outlet. If a pump is used in the system, the flow rate can be measured at the supply stream pump.
Quantify the amount of heat transfer (Btu)
Determine the total amount of heat removed by the heat exchanger.Measure Water Temperature and Flow Rate.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure water flow of fluid 1 and fluid 2 entering or leaving the heat exchanger.
Measure the water temperatures of fluid 1 entering, fluid 1 leaving, fluid 2 entering, and fluid 2 leaving the heat exchanger.
Measurement Locations
Further Reading
Apogee Interactive (2022). “Free Cooling.” Commercial Library. https://c03.apogee.net/mvc/home/hes/land/el?utilityname=union-power&spc=cel&id=1094; accessed February 4, 2021.
ASHRAE (2019). ASHRAE Handbook: HVAC Applications. Chapter 48. DESIGN AND APPLICATION OF CONTROLS. I-P Edition.
ASHRAE (2020). ASHRAE Handbook: HVAC Systems and Equipment. Chapter 40. COOLING TOWERS. I-P Edition. Carrier (2016). “How to Model a Waterside Economizer Application.” Carrier Engineering Newsletter, Vol. 4, Issue 1.
Gordon, J.M.; Ng, K.C. (2001). “Cool Thermodynamics: The Engineering and Physics of Predictive, Diagnostic and Optimization Methods for Cooling Systems,” Cambridge: Cambridge International Science Pub; pp. 159-177.
Trane (2008). “’Free’ Cooling Using Water Economizers.” Engineers Newsletter, Vol. 37-3. Also available at https://www.trane.com/Commercial/Uploads/PDF/11598/News-%20Free%20Cooling%20using%20Water%20Economizers.pdf; accessed February 4, 2021.
Trane (2010). CDS-PRM001-EN. TRACE 700 User’s Manual-Building Energy and Economic Analysis, Version 6.2; pp. 43-49. Also available at https://tranecds.custhelp.com/ci/fattach/get/55941/0/filename/FreeCooling%5B1%5D.pdf; accessed June 17, 2022.
Taylor, S (2014). “How to Design & Control Waterside Economizers,” ASHRAE Journal, Vol. 56, No 6. American Society of Heating, Refrigerating and Air Conditioning Engineers; pp. 30-36.
Trane (2016). “Waterside Economizers - Keeping the ‘Free’ In Free-Cooling.” Engineers Newsletter, Vol. 45-2. Also available at https://www.trane.com/content/dam/Trane/Commercial/global/products-systems/education-training/engineers-newsletters/waterside-design/ADM-APN058-EN_06012016.pdf; accessed February 4, 2021.