Hooked on Hydronics Blog

You can purchase the best pump in all the world for your commercial HVAC system but, if it is installed improperly, it will mean additional costs in replacement parts, labor expenses and equipment down time. If you want to keep commercial pumps running for the long haul, you need to insure that best practices are followed, starting with the initial installation.

I’ve been in the commercial HVAC rep business for over 15 years now and have helped many people design and select boiler systems for their buildings. Yet, the sizing of these systems is most always derived from a load calculated by a mechanical engineer (which I am as well, by the way – see my other blog “Is Your Commercial Boiler System Oversized”). As we run into bitter-cold days here in the Carolinas, (what we in the engineering field call “Design Days”) I cannot help but wonder, how close were we in sizing these systems for actual conditions?

If you are a building owner or have designed systems for owners, on these really cold days, have you ever checked the boiler plant to see how it is running? On Design Days, which present the worst-case conditions your building should see throughout the year, is your boiler plant running at 100% capacity? If you have multiple boilers, are all of them firing at 100%? Are your variable speed pumps running at 60-Hz (100% speed)? And, if the answer is “Yes" or the answer is “No," is that a good thing? The point is to learn what we can about a system from this answer.

Pump Cavitation. Even if you don't know anything about HVAC pumps, you would probably think this is a bad thing. And, you would be right!

Most modern HVAC equipment modulates, or varies, its speed in order to conserve energy while operating at part-load conditions (any condition less than maximum). Full load conditions are realized rarely, usually only a handful of hours per year, which makes performance at part-load pretty important. For HVAC pumps, operating at part-load conditions could result in significant energy savings since, according to the pump affinity laws, horsepower varies with the cube of the flow. For example, reducing a 600-GPM pump using 22-bhp to 300-GPM would only require 3-bhp.

Active Chilled Beams (ACBs) are capable of delivering up to 1500-BTUs per Liner Foot of beam of sensible cooling when supplied with medium temperature (55°F-58°F) cold water. The same coil may be used for heating when supplied with hot water. In either case, air movement is induced by the primary air ducted in from the ventilation system. ACBs are compatible with virtually any ceiling configuration, save vertical space, and are extremely quiet. When applied correctly, they contribute to superior cooling, heating, and ventilating performance in highly efficient and comfortable HVAC systems. And, they do all this with no moving parts!

Earlier, in the blog post “Why Air Must Be Removed from Hydronic HVAC Systems," we discussed several of the issues free air and dissolved air may present in your system. Most systems designed today include an Air Elimination System. That is, they include a separator tank that vents air out to the atmosphere. However, many older buildings were fitted with an Air Control System where the separator tank vents the air to a plain steel expansion tank and never really removes the air from the system.

Utilizing Variable Frequency Drives (VFDs) for HVAC pump motors is a widely accepted practice due to its energy-saving opportunities. These savings come from balancing the pumps with the VFDs in lieu of throttling valves (that add friction to a system) and from simply modulating water flow based on system demand. Some might argue that all HVAC pumps should be driven by VFDs if for no other reason than allowing the soft-start feature to prolong the life of the equipment (as opposed to starting across-the-line at 100% speed). Did you know there are also efficiency advantages that may be realized within the pump itself?

Dedicated Outside Air Systems (DOAS) are quite common today in commercial HVAC building designs. A big reason for this are the Indoor Air Quality (IAQ) requirements from standards such as ASHRAE 62.1, which involves introducing more outside air into a building than ever before. Fresh air is generally good – occupants are allowed to be happier, healthier, and more productive. But fresh air also carries moisture, especially here in the Carolinas. Gone unchecked, high moisture content in the air (high humidity) can lead to occupant comfort and health issues, such as physical discomfort and bacteria and mold growth, and can cause other issues like surface sweating, condensate pooling, and electrical equipment issues.

Let’s start by pointing out the obvious – there is a motor. The motor uses electricity to rotate the shaft that rotates the pump impeller. The impeller, typically made of bronze or stainless steel, is shaped like a wheel. This wheel contains enclosed vanes that sling the water. (Imagine a tennis backhand swing.) So, an impeller slings water, while a propeller pushes water. (Imagine a boat motor.)

I’ve been in the commercial HVAC rep business for over 15 years now and have helped many people design and select boiler systems for their buildings. Yet, the sizing of these systems is most always derived from a load calculated by a mechanical engineer (which I am as well, by the way – see my other blog “Is Your Commercial Boiler System Oversized”). As we run into bitter-cold days here in the Carolinas, (what we in the engineering field call “Design Days”) I cannot help but wonder, how close were we in sizing these systems for actual conditions?

If you are a building owner or have designed systems for owners, on these really cold days, have you ever checked the boiler plant to see how it is running? On Design Days, which present the worst-case conditions your building should see throughout the year, is your boiler plant running at 100% capacity? If you have multiple boilers, are all of them firing at 100%? Are your variable speed pumps running at 60-Hz (100% speed)? And, if the answer is “Yes" or the answer is “No," is that a good thing? The point is to learn what we can about a system from this answer.