HVAC Archives - JDB Engineering, Inc.

Dec 14 2017

Putting the “V” in “HVAC”: Ventilation

By Richard M. Lindemon, PE, LEED AP

Most people are familiar with the abbreviation “H-V-A-C,” whether in full detail or nothing beyond reciting the four letters in succession. Sometimes people try to pronounce it as a two-syllable acronym, “H-VAC,” which may be as divisive as you can get among those in the trade! Still, others will offer that to be technically complete you should add an “/R” to it for Refrigeration, but let’s just set that aside for now.

Basically, the abbreviation quite literally stands for “Heating, Ventilation, and Air Conditioning.” For the most part, people are familiar with, and easily grasp the concepts of, heating and cooling the indoor environment simply from a comfortable space temperature management standpoint. Moreover, humidity control is also widely understood as a key component of air conditioning from an indoor environmental comfort point of view. That would generally take care of the “H” and the “AC,” but what about that “V” in between? Among the people who know that the “V” stands for “ventilation,” how many of them know what “ventilation” really is? It is likely the most misunderstood element of the abbreviation itself.

Try asking anybody this simple question – “What is ventilation?” – and you will get more answers than you thought possible. Simply stated, “ventilation” is “fresh air” – nothing more, nothing less. The term “fresh” is loosely used here because you can have extensive debates on what constitutes “fresh” air, but we’ll just accept the notion that “fresh air” is the air outside as opposed to that within a room or other enclosed space.

So, what do we need to do with this fresh outside air that somehow became the “V” in HVAC? We need to bring it inside, that’s what we need to do with it. Why? Because it’s good for you. When I was a child, my mother was always telling me, “Go play outside. The fresh air is good for you.” She probably knew more about the “V” than even she realized. So, to avoid throwing this respect for authority to the wayside, our building and construction codes have also convinced us that fresh air is good for us, because they have mandated that buildings must incorporate a minimum amount of fresh outdoor air for proper ventilation of occupied spaces. The primary purpose is to protect building occupant health by controlling the quality of indoor air from the effects of airborne contaminants, which can be damaging. Additionally, ventilation is required to protect the building itself from the harmful effects of excessive heat and humidity.

Methods for bringing fresh outdoor air into the building environment include “natural” ventilation and “mechanical” ventilation. Natural ventilation is essentially the effect of opening a window or door to let fresh air enter freely into the building. It can be effective, but very unpredictable as natural air movement is dependent on many parameters – both naturally and humanly controlled – that must be met consistently. We all know that Mother Nature is rarely consistent, and humans can be unreliable at times as well.

Mechanical ventilation uses fans or blowers to force movement of air to and from occupied spaces. This equipment is either dedicated to providing ventilation or can be part of a heating, cooling, and air-conditioning system that serves the spaces to be ventilated. In either method, the fresh outdoor air brings with it the outside temperature and humidity conditions that conflict with the indoor environmental conditions we are trying to establish with our “H” and “AC.” To bring the outside conditions in line with our indoor conditions, we must provide additional mechanical energy to heat, cool, and control humidity of the outdoor air required for ventilation – in addition to offsetting the building and space loads. This creates additional cost for larger capacity HVAC equipment as well as increased energy consumption. The conditioning of outdoor air for ventilation can represent 20% to 50% of a building’s thermal load, depending on the quantity of air required and the seasonal thermal conditions.

Overlooking the “V” when planning a building project can not only jeopardize the health of your building and its occupants, but can also lead to the surprise of additional life cycle costs associated with purchasing, supporting, and operating your HVAC systems.

Got a question about the “V”? Or even the “H” or “AC”? We’ve got you covered! Reach out to Rich Lindemon via email or 717.434.1563.

Bigger Isn’t Always Better! Why Oversizing Packaged DX Rooftop Equipment Isn’t a Good Idea

Oct 31 2017

Bigger Isn’t Always Better! Why Oversizing Packaged DX HVAC Equipment Isn’t a Good Idea

By Rich Lindemon, PE, LEED AP

It is very easy to fall into the trap of thinking that bigger is better when you consider something that you like or enjoy or that benefits you and those around you. That super-sized value meal with the extra-large fries and drink must be better than the regular sized portions. An extra 100 horsepower out of your car’s engine can make you go faster whenever you want. Who wouldn’t want a 70-inch TV on the wall of their family room, right? But that line of thinking doesn’t always apply favorably to all things, and it’s probably easy to come up with several of them rather quickly. One that is often overlooked is thinking that a bigger air conditioner must be better because it would have the ability to condition a space quicker and easier, and never fall short on capacity. There are several flaws with this way of thinking, which demonstrate that in the case of oversizing packaged direct expansion (DX) HVAC equipment – bigger is NOT better.

Before getting into the reasons why oversizing DX HVAC equipment is a bad practice, we should start by noting that all HVAC equipment should be sized using proper heating and cooling load calculations. There are several methods for doing this, but bypassing this critical design step in lieu of a “Rule of Thumb” method or a generic load-per-square-foot will usually get you off to a bad start. An accurate load calculation will allow you to select the correct size HVAC unit. Once you know your load demand, you need to focus on why you are designing an air conditioning system in the first place – usually simply for comfort. Comfort results from properly controlling the temperature, relative humidity, and air circulation uniformly and consistently through the space. In most cases, we concentrate primarily on regulating the temperature because we want it cooler when we feel uncomfortably warm. But we also feel uncomfortable when the humidity levels are too high. This heightened sensation of heat causes the desire to try to compensate by lowering the set point on the thermostat. This in turn causes the unit to overcool the space, leading to a more uncomfortable environment. A right-sized HVAC system that is properly matched to the calculated load will operate far more efficiently than an oversized unit. An air conditioning system that doesn’t run efficiently can unnecessarily drive up energy costs, going against today’s focus on creating a sustainable environment.

When an air conditioner runs, it does two jobs. It lowers the temperature of the space while also removing moisture from the air. To do the second task, it must run for a long enough time to allow the water to condense out of the airstream. Oversized air conditioners typically do not run long enough to completely dehumidify because they satisfy the space temperature and then shut off. As the space temperature rises again the unit will start running, but then quickly shut off when the space temperature setpoint is reached. This is called short-cycling and leads to another problem with an oversized air conditioner. As it short-cycles frequently – “bang on, bang off” – it takes far more initial energy to start the unit as it does to maintain continuous operation, leading to increased wear and tear on the components, particularly the compressor. An oversized short-cycling packaged DX air conditioning unit will not only fail to satisfy all the required comfort conditions, but it will ultimately fail completely long before reaching its life expectancy.

While sacrificing human comfort with an oversized packaged DX HVAC system, you may also be causing inadvertent damage in other areas as well. These include the building structure, personal health, and lifecycle costs. Limiting the ability to properly condition the space and control moisture can lead to environmental issues like the development of destructive organic growth that can damage your building structure. Indoor air quality can suffer greatly, leading to all sorts of potential health risks. Ultimately, you will pay more to purchase, install, operate, and repair an oversized HVAC unit that will also fail prematurely.

Now, about that supersized value meal…

JDB Engineering offers a full complement of HVAC services. Learn more here. Questions about this post? Reach out to Rich Lindemon, PE, LEED AP.

Jan 12 2017

Trying to Reduce Energy Consumption in Your Plant? Check These Two Important Components

By Timothy A. Warren, PE, LEED AP BD +C

Continuing our conversation on industrial energy reduction that started here, we will discuss energy reduction for compressed air and pumping systems.

Compressed air.

This is probably the most expensive form of energy used in an industrial plant because of its poor efficiency – with an efficiency rating of typically 10%. Because of this, compressed air should be high on your target list if it is not already. There are more than a dozen measures that can be considered to reduce energy use for compressed air plants.

Here are three major ones:
1. Reduce leaks
• Typical plants that are poorly maintained have 20-50% leak rates
• Leak repair and maintenance can reduce the leak rate to 10%
• Overall, leak repair could reduce annual consumption by as much as 20%
The most common areas for leaks are couplings, hoses, fittings, regulators, traps, valves, and disconnects. Quick disconnects are notorious for leaking and should be avoided. Detecting methods include manual inspection as well as ultrasonic acoustic detection. Leaks will continue to occur, so detection and correction programs need to be ongoing efforts.

2. Use alternate sources for specific applications:
Source: ENERGY STAR

This measure is very interesting when you think about how many processes utilize compressed air within manufacturing plants. Some industry engineers believe this measure has the largest potential for compressed air energy savings, as many operations can be accomplished more economically and efficiently by using other sources.

3. Reduce inlet air temperature
• Each 5 degree F will save 1% of compressor energy
• There is usually a quick payback of 1-5 years
• Approaches to reduce air inlet temperature include:
– Duct inlet from outside
– Duct exhaust air (cooling air) to outside
– Ventilate room
– Heat recovery

It seems somewhat obvious, but when walking through mechanical rooms I’m never surprised to find the rooms with air-cooled compressors are super-hot, with compressors utilizing room air, or worse yet, discharging the radiator exhaust air directly to the space! From a design perspective, we always try to duct inlet air directly from the outdoors. The worst case would be that we have the compressor use room air, duct the exhaust to the outside, and ventilate the space very well. In addition, we always try to include a damper arrangement in the exhaust duct to utilize the rejected heat for space heating when needed.

Pumps.

To reduce pump demand, a sound approach is to eliminate bypass loops, which can result in energy savings of 10% to 20%. Constant volume pumping was a traditional approach before the advent of smarter control strategies and capabilities. Although constant volume pumping provides very predictable controls to meet requirements, the energy use is often overlooked. Not surprisingly, there are a lot of these systems still in operation.

Bypass loops are devices that maintain constant flow in the main circuit. For example, a three-way valve serving a chilled water coil allows variable flow through the coil, but maintains constant flow in the main loop. Other similar devices can be in the main circuits. By eliminating these devices, we allow the pumps to operate closer to actual demand and at a lower brakehorsepower, basically riding the pump curve. This is not as efficient as speed drives, but certainly is a step in the right direction.

When properly sizing pumps, it is critical to trim the pump impeller and minimize throttling valves, which can result in energy savings of anywhere from 15% to 20%.

Once we know the design condition (flow and head), we select a pump with the best operating characteristics. For this example, let’s say that we have 600 gpm at 70 ft. head design condition, with a 9”diameter impeller. The balancer goes to balance the pump and realizes he’s getting 750 gpm. What does that mean? The actual pressure drop is less than expected so the pump is over-achieving. To balance to the design flow, the balancer would typically use the triple duty valve to throttle the system to induce additional pressure drop in the system.

Is this energy efficient? Of course not!

Instead, a system curve should be developed using the pump affinity laws and a pump curve to determine what impeller size is really needed. Upon doing so, we find that a smaller impeller would give us the required flow at a much lower brakehorsepower. For this example, the pump would operate at 50% of the brakehorsepower with a trimmed impeller compared to the throttling scheme. Keep in mind, this is not only for new installations. This checkup can be done with any existing pump, knowing the flow demand at full load conditions.

Variable speed drives should also be considered to address variable demand. However, this is not applicable for systems with high static head, open systems, or for systems with extended low-flow conditions.

Variable speed drives are an effective energy measure for pumps with variable demand. Rather than just riding the pump curve as a constant speed pump, pumps with variable speed drivers will continuously match speed and power to actual demand requirements, thus maintaining operational efficiency throughout the pump’s operating range.

Questions about reducing energy in your industrial facility? Contact Tim Warren at 717.434.1566 or twarren@jdbe.com

Jun 08 2016

Scott Butcher Presents to SMPS Chapter

Scott D. Butcher, FSMPS, CPSM, vice president and chief marketing officer of JDB Engineering, Inc., recently presented to the Society for Marketing Professional Services (SMPS) Northeast Ohio chapter in Cleveland. His topic was A/E/C Business Development – The Decade Ahead, a presentation he developed for the SMPS Foundation, a non-profit research organization for which he is Past President. Scott has given this presentation more than a dozen times, and he served as co-chair and co-author for the companion book, A/E/C Business Development – The Decade Ahead, which was published by the SMPS Foundation in 2013.

Feb 29 2016

When Do Variable Refrigerant Flow (VRF) Systems Make Sense?

by Kevin G. Angle, PE, LEED Green Assoc.

Having three young children at home, I hear all kinds of music in the car and in the house. Lately, my kids have become excited when Meghan Trainor’s “All About the Bass” comes on the radio – I regularly listen to all three of them in the backseat of the car screaming the lyrics. While writing this post, I was tempted to title it “VRF – It’s All About the Application.” VRF, which is also called VRV, has gained popularity as a newer technology in the United States. This type of air conditioning system utilizes Variable Refrigerant Flow (or Volume).

VRF systems are often viewed as an enhanced version of ductless split systems, which have been successfully installed for many decades. The term “variable refrigerant flow” refers to changing the flow of refrigerant to each indoor unit. The Variable Refrigerant Flow enhancement comes with multiple indoor unit evaporators or condensers, up to 16 with various manufacturers, utilized with a single outdoor condensing unit or heat pump. Due to the advanced use of variable speed compressors, drives, and inverter-driven fans, many manufacturers of these systems are capable of providing simultaneous heating and cooling through their indoor units. Most manufacturers refer to these as heat recovery systems, and they have various methods of recovering the heat through either a two-pipe or three-pipe system.

Now that we know the capabilities of a VRF system, when does it make sense to use it? It’s all about the application (queue the music!). On the renovation of a relatively small government housing project (5,000 sq. ft.), we were tasked within the design criteria to provide a central HVAC system that also provided individual temperature control within each dormitory room. In addition, we had to meet the design requirements of a LEED-certified building, which requires energy savings of 30% compared to the baseline system. Those two criteria limited our options and led us in the direction of VRF. In the end, VRF and geothermal systems were the only two systems able to meet the energy savings.

So we know that the application of VRF works for a smaller building, but is it an option for larger buildings? I would say yes – but again, it’s about finding the right application. VRF systems are good for potential high-rise buildings, which have varying exposures and varying loads throughout the building. VRF heat recovery systems will perform well where one space may need heating, while the adjacent space may need cooling. VRF systems are expensive in terms of first cost – in many cases 2 to 2.5 times compared to a traditional packaged DX system. However, our energy models are indicating that in some cases, as much as 50% energy savings may be achieved when compared to baseline systems. Also, it is important to note that VRF systems do require a dedicated outdoor air system to meet ventilation codes, which in many cases adds to the first cost. Buildings with operable windows or natural ventilation are prime candidates for VRF. VRF also makes sense for historic renovation projects, where it is easier and less invasive to install refrigerant piping than larger hot or chilled water piping, along with associated ductwork.

VRF systems have been used with some success for larger assembly spaces; however, indoor units are typically limited in capacity to approximately 3-5 tons of cooling. As a result, VRF systems may not be the best solution for this application or for any type of industrial or manufacturing building. Albeit a newer technology with many uncertainties surrounding the reliability of energy models, actual savings in labor, and first cost, VRF systems have proven to have a spot in the marketplace with the right application. VRF systems are not new to Europe, and have been successfully used there for more than twenty years, which must say something.

The VRF Checklist

VRF Infographic

Real-World Applications for VRF Systems