Are Economizers for Process Chillers Getting Missed By the Engineering Community? Just Maybe?

Posted Tuesday, 29 March 2016 14:42 by Martin King in HVAC Business

Guilty As Charged

Yes, I am obviously an advocate for proper application of economizers for smaller (1-20) ton process chillers. I have a lot of friends within the mechanical engineering community that just about all say, "Wow, that's a great idea!" (as in, you go Martin!)... Yet, when it comes to specifying an economizer for a smaller process chiller, they gloss over the subject. Every once an a while I get the, "Well, the end user does not understand what an economizer is, so they will not pay for it." Good grief I say!

For those of you who do not know me, I have been tinkering with application of economizers on smaller mission critical chillers since the early 2000's. As I experimented with the concept, it just seemed smarter to reject process heat to the outdoor air, or a water source in the case of a water-cooled chiller, rather than running traditional mechanical refrigeration at a much higher cost and net environmental impact. As my design evolved into a potentially viable market opportunity,  I applied for and was granted a broad scope US Patent for process chiller economizers in 2007. Yay for me, you say?  Frankly, I would probably not do it again, and that's another story :-)

Getting To the Point

With my appreciation for brevity, and to prevent the aforementioned gloss over, I will pick one of my favorite real world applications as the focal point of this post.  

For some time now, medical imaging and treatment systems, such as MRI, CT, PET and LINAC, have been in our sights.  Namely their 24/7 operation, high readability requirements and relatively high chilled fluid set-points (that range from 55-65F) make these systems a particularly good fit for our economizer technology. With some good old fashion cold weather, generally an abundant commodity throughout the northern USA and Canada, the math points to some some attractive ROI's even the most conservative bean counters have a hard time passing up. 

Before we jump into the math, let me share a very basic sniff test that could stop economizer consideration cold: To be financially viable, the operating environment must provide at least a ten degree (F) difference between the economizer cooling medium (generally this is outdoor air in the case of an air-cooled condenser chiller or a water in the case of a water-cooled condenser chiller) and the process fluid servicing the load. For example, if your site is located in Phoenix and your process requires 45F, application of an economizer just does not pencil out. 

Lets Crunch Some Numbers, Shall We?

 In this example, we will use Legacy's economizer audit tool, available for download from our KB, to analyze ROI and see if the additional investment in economizer technology pencils out.

Some Data Points For Our Analysis

Our customer is looking to replace an existing process chiller for a GE Signa 3.0T MR750 MRI. Legacy's OEM solution for this MRI is a PZAT18D (15 ton) process chiller. Our target site is located in the greater Chicago area, and the MRI site prep documentation calls for a process approach temperature ranging from 55-65F. For the purpose of this review, we will pick a process approach temp of 60F.  Considering the old chiller is located outdoors, the customer plans to run 40% glycol concentration to prevent freezing. 

After talking with the hospital administrator, we have learned that their power rate averages .10 per kilo watt/hour and we also have taken the time to research the breakdown of how the hospitals utility company generates their power. This is generally represented as a mix of nuclear, hydro-electric, and fossils fuels. 

Lets Do the Numbers

First, we need to input the site data. Below is a screen shot of the data we collected from our target zip code for the city of Chicago. 

Next, we will input the proposed equipment data. This data was taken from the Legacy submittal on the PZAT18D model chiller available for download on the our site. 

Next, lets have a look at the potential economizer savings. This screen indicates a potential annual "Operating Cost Reduction of $5,350", with an equivalent annual CO reduction of 3,331 LBS.  

Lastly, we will have a look at the all mighty Return On Investment (ROI). This screen indicates a potential ROI of .84 months. Important note, the "Nexus upgrade costs" indicates the added end user NET cost to add Nexus Technology to a standard process chiller.   

In addition to the potential energy savings and related CO reductions, an economizer (via Legacy's Nexus Technology) also reduces wear on a chillers mechanical refrigeration system. This reduced wear has the potential to reduce service and maintenance costs over time. 

For more information on process chiller economizers, Nexus Technology, or to get a copy of Legacy's energy audit tool used to perform the above calculations, contact Legacy Chillers @ 877-988-5464 x 101. 

Lastly, on  Tue, Apr 12, 2016 9:00 AM - 9:45 AM PST, Legacy Chiller Systems is hosting a webinar titled "Nexus Process Chiller Technology - Introduction" - Click here to sign up today