[Paper Review] Energy optimization in ice hockey halls I. The system COP as a multivariable function, brine and design choices

Andrea Ferrantelli, Paul Melóis+2 more|arXiv (Cornell University)|Nov 2, 2012

Wind and Air Flow Studies16 references3 citations

TL;DR

This paper proposes a functional optimization approach to maximize the system Coefficient of Performance (COPsys) in ice hockey halls by modeling COPsys as a multivariable function of brine properties, pipe design, and operational parameters. It finds that brine type and specific heat are critical for performance, with ammonia outperforming ethylene glycol, and that pumping power contributes only ~7% to total energy use, making it a minor optimization target compared to chiller and compressor efficiency.

ABSTRACT

This work is the first in a series of articles addressing the energy optimization in ice hockey halls. Here we adopt an analytical method, called functional optimization, to find which design and operating conditions maximize the Coefficient Of Performance of the entire cooling system (brine pumps and cooling tower), which we call ${ m COP}_{sys}$. This is addressed as a function of several variables, like electric consumption and brine physical properties. By maximizing such function, the best configuration and brine choices for the system can thus be determined accurately and rigorously. We investigate the importance of pipe diameter, depth and brine type (ethylene glycol and ammonia) for average-sized ice rinks. An optimal brine density is found, and we compute the weight of the electric consumption of the brine pumps on ${ m COP}_{sys}$. Our formulas are validated with heat flow measurement data obtained at an ice hockey hall in Finland. They are also confronted with technical and cost-related constraints, and implemented by simulations with the program COMSOL Multiphysics. The multivariable approach here discussed is general, and can be applied to the rigorous preliminary study of diverse situations in building physics and in many other areas of interest.

Motivation & Objective

• To address the high energy consumption in ice hockey halls, which typically exceed 1,800 MWh/year.
• To identify design and operational parameters that maximize the system COP (COPsys), defined as the ratio of cooling load to total electric consumption.
• To evaluate the impact of brine type, concentration, pipe diameter, depth, and number of pipes on system efficiency.
• To validate the model using real-world heat flux and temperature measurements from a Finnish ice rink.
• To provide practical, cost-constrained design recommendations for energy-efficient ice rink refrigeration systems.

Proposed method

• The study employs functional optimization (FO), a multivariable analytical method, to model COPsys as a function of electric consumption, brine physical properties, and system parameters.
• COPsys is derived from theoretical formulas and validated using experimental data from a 2009 ice rink in Leppävaara, Finland, with measurements of heat flux and interface temperature every five minutes.
• The method evaluates the sensitivity of COPsys to variables including volumetric flow rate, brine density, specific heat, pipe diameter, depth, and number of pipes.
• Simulations using COMSOL Multiphysics are conducted to analyze thermal performance and temperature uniformity across the ice surface under different pipe configurations.
• The model is constrained by technical limits such as concrete slab thickness, insulation load capacity, and pipe spacing, and validated against real-world cost data.
• A cost-benefit analysis is performed to compare the economic impact of increasing pipe count from 150 to 200, considering installation and fluid costs.

Experimental results

Research questions

• RQ1 What is the optimal brine type and concentration that maximizes COPsys in ice hockey halls?
• RQ2 How sensitive is COPsys to variations in volumetric flow rate, pipe diameter, and pipe depth in the concrete slab?
• RQ3 Does increasing the number of pipes from 150 to 200 significantly improve thermal uniformity and system performance?
• RQ4 What is the relative contribution of brine pumps versus compressors and condensers to total electric consumption?
• RQ5 Can the functional optimization method be used to guide cost-effective, energy-efficient design decisions in ice rink refrigeration systems?

Key findings

• Pumping power accounts for only ~7% of total electric consumption, making it a minor contributor to system inefficiency.
• COPsys is not significantly affected by volumetric flow rate or pipe diameter and depth, which have minimal impact on system performance.
• A critical brine density exists at which COPsys is maximized, independent of the specific brine type.
• Ammonia provides a higher COPsys than ethylene glycol due to its superior specific heat capacity.
• Ethylene glycol is recommended only at concentrations between 20% and 34% to avoid bacterial growth and ensure optimal performance.
• Increasing the number of pipes from 150 to 200 improves temperature uniformity at the ice surface, though at a cost increase exceeding 50%.