Hydronic Air Handlers + Condensing Boilers = Greater System Efficiency

The article below is a guest post from Roy Collver, President, OTBC Inc. Roy teaches Condensing Boilers in Hydronic Systems, a 6-week course where students optimize system designs and control strategies to take full advantage of the energy savings and comfort benefits boilers have to offer.

Who Should Read This: 

• Heating professionals
• Radiant heating experts
• Heating installers
• Heating engineers

Learning Takeaways: 

• ECM technology is going to have a huge impact on the system efficiencies of Hydronic systems that use air handlers (fan coils) for heating and cooling.
• Everything in a hydronic system is related to everything else, and those who can see clearly how new technologies dovetail together to make a superior “whole” are the people who drive the next round of innovation.
• The average heating system only has to operate at its highest output level for less than 10% of the heating season.
• Modulating / Condensing (Mod-Con) boilers, operate most efficiently when they are heating low temperature water, and when they are operating at their lower input ranges
• A well-designed microprocessor-based control system acts more like a committee – it can be more subtle. It “sees” more things going on, and it has many more choices for measured action, but you do need clever engineers and programmers to understand how to best get the most out of every component and how to best make all of them work together.

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Using an air handler with a hydronic coil for space heating has had its ups and downs. Hydronicians – long enamoured with radiant floor heating as the ultimate in comfort and energy efficiency have largely relegated hydronic air handlers to lowest status in the “best choice” category of heat terminal units – not anymore. In the past, air handlers were considered noisy, subject to creating discomfort by alternately blowing hot and cold air, difficult to zone, and not very energy efficient. The times they are a changin’ however, and advances over the last twenty years have put the best of these devices into contention as perhaps the most comfortable and energy efficient way to heat many types of structures. What has changed?

In a word – ECM – an acronym for “Electronically Commutated Motor”. The ECM motor instantly makes the once lowly air handler a perfect and harmonious dance partner in today’s hydronic systems.

There is lots of information on the web to teach you all about these devices, so I will leave it to those who are interested, to search the words “ECM Motor”. This article will help show how this technology is going to have a huge impact on the system efficiencies of Hydronic systems that use air handlers (fan coils) for heating and cooling. Everything in a hydronic system is related to everything else, and those who can see clearly how new technologies dovetail together to make a superior “whole” are the people who drive the next round of innovation. Those visionaries who proposed and quarterbacked the development of the P.10 and P.9 integrated mechanical system and combo system standards, did so because they saw this all coalescing long before most of us did. They understood that combining all of the components of a mechanical system together in a truly unified package, would result in maximum system energy efficiency. They also saw that the required technology was rapidly maturing, and we could soon “do this”. So what part does the ECM Motor play? A big one.

ECM motors operate air handler fans at lower Watts per CFM, than the currently “standard” PSC (Permanent Split Capacitor) motors. But even more importantly – their speeds can be very accurately regulated at any point, all the way from stop, to full speed and back to stop again; and the BEST news is, these fans deliver their most impressive performance at lower speeds and static pressures with almost full torque! I first read about them some 20 years ago, and when I chewed on the possibilities, I was immediately hit with “the vision”.  Many other hydronicians would instantly “get it” also upon learning what ECM brought to the table. What was this insight? Time for a little guessing game:

1. The ECM air handler fan motor is more efficient at its lower output levels – – what other high-energy consumption hydronics device is also more efficient at the lower end of its output range?
2. What percentages of the season does a heating system require a full, medium or low input of heat?
3. What other major technology has taken the hydronics world by storm in the last twenty years – one that can help more easily optimize the integration of mechanical HVAC systems?

Answer those three questions, and you should see the same bright flash I did – stay with me here. Although some manufacturers (those who still have an R&D budget) have been dabbling with this for over a decade, it has taken awhile for the equipment to come down to a more edible price point. We’ve been waiting patiently, and lately it is looking like this approach could come into the mainstream at last.

Here are the quick answers, along with some “picture worth a thousand words” illustrations I put together for this article.

1. Modulating / Condensing (Mod-Con) boilers, operate most efficiently when they are heating low temperature water, and when they are operating at their lower input ranges. Using outdoor reset with air handlers is now viable because we can slow down the fan and reduce the velocity so people don’t feel “cold” air blowing on them. Now the condensing boiler can condense all of the time, and give you more efficiency than that AFUE number everyone lives or dies on – see illustration #1. Bonus – we can reduce the boiler firing rate, and squeak out a few more points of efficiency by running at lower-firing rates much more often – see illustration #2.

 

Illustration 1 – The lower you go (water temperature) the more efficient a condensing boiler becomes

 

Illustration 2 – At high fire, most boiler heat exchangers just can’t handle the heat and some of it sneaks by (up the chimney)

2. The average heating system only has to operate at its highest output level for less than 10% of the heating season. Around 60% of the heating season most systems operate below half of their design output range, and for 30% of the season, they can purr along at the bottom end of their modulation range. The chart – illustration #3 – was developed by NRCan to clearly show this phenomenon. It justifies/explains how they test output levels for the P.10 Integrated Mechanical Systems, and the P.9 Combo Space Heating and DHW Systems

 

 

Illustration 3 – This chart makes it easy to see why lower, part-load output performance is more important for over-all efficiency

Illustration 4 – Outdoor reset takes the water temperature below the condensing range most of the heating season

3. Microprocessor controls can put all of the pieces together to provide coherent operation of a whole system to attain maximum efficiency. They are the keystone of integrated mechanical systems, and many people still don’t realize just how different they are when it comes to operating a heating system. The old thermostat was like a Drill Sergeant yelling in your ear “GO HARD! It’s too cold in here!” – then all of a sudden without warning, “STOP NOW! It’s too hot in here”. A well-designed microprocessor-based control system acts more like a committee – it can be more subtle. It “sees” more things going on, and it has many more choices for measured action, but you do need clever engineers and programmers to understand how to best get the most out of every component and how to best make all of them work together.

 

 

Illustration 5 – Microprocessor controls are the key to putting all of the pieces together – they are getting to be really busy places

What does this all mean for comfort and efficiency?

Far more people in our industry need to understand the potential or this pairing of components. A revolution won’t occur overnight, but we are starting to see some incremental changes in equipment and controls happening right now. Dealing with two appliances that both modulate their outputs is a slippery business – get it wrong, and all kinds of strange things can happen. Other changes will need to occur in lock step. More efficient ductwork and air distribution is required to provide adequate circulation at lower fan speeds. Ventilation requirements have to be woven into the whole. If we get it right, I think we will be seeing net zero buildings as a viable and common option in the very near future. Stay tuned.

About Roy Collver, President OTBC, Inc & Expert Instructor, Condensing Boilers in Hydronic Systems:

Roy is a Hydronics Specialist / Educator, Class 1 Gas-Fitter and Illustrator.  Roy has applied his creative force and problem solving abilities toward the improvement of hydronics in North America for over 35 years. His varied experience at the very cutting edge of new development in hydronics has allowed him to apply his unique knowledge and skill set toward becoming a premier “translator” of new technology to a traditionally conservative and slow-to-change Industry. His training is up-to-date, comprehensive, and entertaining. After ten years at the top level of his trade “on the tools,” Roy worked closely with many eminent design and application engineers on new and innovative products—from initial concept to final production and marketing. Working in the very “inner sanctums” of these most progressive companies; he was a key partner in helping them design and bring to market, many game-changing hydronics products. He produced many outstanding training programs along with the technical and promotional materials needed to explain the effective application of these new products in the real world.

Keep Learning: 

• Complementary test-drive of Roy’s 6-week online course: Condensing Boilers in Hydronic Systems 
• Enroll in Roy’s free course: How to Design and Sell Mod-Con Boilers 
• Free tool: Savings Estimator Calculator for Condensing Boiler Systems

Copyright © Roy Collver 2014, all rights reserved – distribution and reproduction by permission