Helping to Solve Future Demands for Food

Well...it has been a long, long time since I have posted anything on the blog.  Time flies by at times and it is easy to lose track of the months since the last posting.  However, I am back :-) and will become more diligent in sharing my thoughts with you.

In the last couple of months I have participated in two unique meetings organized by "the Vertical Exchange" folks.  One of the meetings focused on the food industry and the other focused on design/build contractors.  Mestex is  such a diverse division of Mestek that we have solutions for projects in both of those segments...among many others.  There was an overlap between those two markets that might not, at first, seem obvious.

Increasing population densities in many parts of the world combined with changing climates is beginning to impact the ability of food companies to grow quality produce in the volumes needed.  There is also the specialized "boutique" grower who supports the "farm to table" concept in urban environments.  A solution to these scenarios that is emerging is the world of "indoor agriculture".  This goes well beyond traditional greenhouse facilities.  Indoor farms use sophisticated lighting, watering, and nutrient systems to grow produce 24/7/365 in controlled environments.  These facilities can be single story purpose built buildings, multi-story repurposed commercial buildings, or even "modular" buildings similar to modular data centers.  With the exception of the modular solutions all of these projects require the talents of design/build contractors for proper execution.  Even the modular solutions that are "factory built" still require qualified on-site contracting for completion of the project.

From a mechanical design point of view these facilities can be quite challenging.  In order to create an artificial environment for growing plants the power demands of the lights used to create an "artificial sun" will create very high thermal loads.  The watering and transpiration of the plants creates high latent loads on the HVAC equipment.  Providing the necessary CO2 without creating a hazard for employees is also important and, finally, preventing the introduction of pests and unwanted biological hazards requires very high levels of filtration.

In short....the HVAC systems must be able to handle very high sensible loads, very high latent loads, very high filter densities, and include controls that can flush a grow space quickly and efficiently...preferably all in one package!  No small task.

Mestex has had decades of experience providing equipment to the food industry and to design/build contractors.  We are leveraging that experience to develop solutions to the problem of indoor agriculture.  One of the first areas where we are working is in the world of cannabis growing.  This market is unique in that the revenue stream and profits are large enough to justify development of an advanced HVAC solution that accomplishes all of the needed functions in a single package.  The lessons learned in that market will transfer to more cost sensitive indoor agriculture products that can help meet the demands of those markets as well.

For more information about some of the work being done by Mestex you can refer to a couple of articles that were published by Business News Publishing for the 2016 Mechanical Exchange.  This link (http://eblast.bnpmedia.com/News/MXC_0916/MXC.html) will take you to the eblast site where you can open the entire Air Conditioning News supplement.

Equilibrium

Equilibrium…we all try to achieve it in our lives.  An argument can go on forever if both sides maintain a high energy level and refuse to cool things down.  An argument can end when both sides take it down a notch and each reaches a happy place that they can both accept…a state of emotional equilibrium.

Odd as it may seem your air conditioning system is trying to do the same thing…reach a happy state of equilibrium…a balance between the high energy state and the low energy state.  Fortunately the system won’t get there under most circumstances because when the high and low energy states are equal then the unit stops providing cooling.

To simplify our thinking about this, substitute the word “temperature” for the word “energy”.  Now remember back to your days in physics class and remember that energy flows from a high state to a low state until the two states match and then the flow stops.  An air conditioning system takes advantage of that basic law of physics by absorbing the warm energy in a room and sending it to a lower energy place where the warmth is released and the cycle can start all over again.

One problem in this description of an air conditioning unit is that we usually don’t want the high energy released back into our rooms so we have to send that energy outside the room, or building, to get rid of it.  We do that by using refrigerants or water to transport the heat energy.  We also have to be sure that when we send it outside that it is at a higher energy level than the outdoors.  That is why we have compressors (and chillers which are just really big compressors) in our systems.  The compressors act as both a pump and as a device to actually add energy to the fluid that is pumped through the cooling coil in the room.  If you grab the side of a pipe entering a cooling coil it will feel relatively cold.  If you grab the pipe between the coil and the compressor it will feel a bit warmer.  If you grab the pipe on the leaving side of the compressor you might burn your hand.  The system has added enough energy to make sure that when the refrigerant or water reaches the outdoors it is at a higher energy state than the air outside the building.  That can be quite a challenge in a place like Phoenix or Dubai.

Most manufacturers realize that their equipment might be installed in those climates so they pick components in their systems that can operate under those circumstances.  But there are limits to what can be done.

The most widely available commercial cooling systems on the market are DX packaged units.  In order to satisfy the largest market (and sell the most equipment) these units are intended to be used for comfort cooling of people.  Since most people are “comfortable” when their office is around 75 degrees these units are designed around that operating point.  That is their happy point and that is the temperature of the air that is being returned to the cooling coil where heat energy can be absorbed into refrigerant or water and then sent outside to be removed.  The units will continue to operate at higher temperatures but remember that we need to be sure we send the heat outside at a higher level than the air outside. 

If you read the technical manuals for virtually every rooftop unit on the market you will see that, for a lot of really esoteric reasons, that rooftop unit is designed to operate at no more than 90 degrees returning to the cooling coil.  At that point the combination of components in the rooftop unit will be “maxed out” if the outside air temperature is in the 120 to 130 degree range. When the outside air temperature is 135 degrees on a roof in Phoenix then the high energy state and low energy state are so close together that almost no work is done and the temperature of the air coming out of the air conditioning unit starts to go up because the system is no longer rejecting much heat.  The system has quit working as intended and the situation usually spirals out of control as more heat builds up in the refrigerant or water.  Eventually so much heat has built up, and is compounded by the compressor, that the system shuts itself down to protect itself.

So, what does all this rambling have to do with anything?  Most of my blogs lately have been about mission critical/data center energy issues.  It is a big deal, and lots of folks are working on solutions, but economics sometimes trumps clear thinking or limits what can be achieved.

We are seeing more and more data centers specified with DX rooftop packaged units.  While these are normally high quality products they were originally designed to be at a happy place with, at most, 90 degree air being returned to the coil.  In a data center that is being designed to the latest ASHRAE standards the cold aisle can be anywhere between 80.6 and 113 degrees F.  When you allow a 20 degree F temperature rise across the servers before you return the air to the unit then I think you can see the problem.  The rooftop unit is being asked to operate well above its built in safety circuit limits.  Thus you end up with a self-limiting factor on how effective you can be in reducing the operating expense in the data center.  Even if you believe that your servers will be fine at 80.6 degrees F your HVAC unit probably will not be so fine.  And, to be honest, this same logic applies to CRAC units as they are nothing more than split DX systems.  So you have self-limited your options to cold aisle temperatures of no more than about 70 degrees F and your data center costs more to run than it could.

There is a class of rooftop unit that is better equipped to handle these situations and that class of equipment is commonly known as a DOAS, or Dedicated Outdoor Air System.  These systems, like our Applied Air FAP product, have been designed to expect Phoenix type temperatures across the cooling coil.  Returning hot aisle air at 105 or 110 degrees F is well within their “normal” operating ranges.  These systems are more expensive than a conventional rooftop packaged unit because of the components that are selected but they also provide the operating range that will allow the designer and operator to take advantage of the elevated temperatures that ASHRAE and the IT equipment people recommend for reducing data center operating expenses.

Too Hot to Handle? A Simple Reminder

Well, this is embarrasing.  I have been in the HVAC industry for over 40 years now and have helped design and manufacture some of the more sophisticated products that have been introduced.  But, in spite of that I have to admit that I messed up.  And the lesson that I was reminded of can help you too if your residential, commercial, or mission critical system is struggling to keep up with the heat.

Over the past couple of weeks the temperature here in Texas has been over 100 degrees F every day...sometimes up around 105 to 110.  That is nothing unusual for Texas in the summer and not as bad as last year.  But I started to notice that my residential HVAC unit was no longer able to maintain my thermostat setpoint of 77 to 79 degrees F.  The system was consistently running 3 degrees behind and running non-stop...and was only installed a year ago.

Refrigerant leak?  Undersized?  Dog left the door open?

No...it was one of the most common problems in any HVAC system that is not running correctly...the condenser coil was coated with a fine film of dirt.  Let me repeat that...a FINE film of dirt.  Not clogged...not even very obvious at a quick glance...a FINE film.  In my case it was actually a fine film of dryer lint since the clothes dryer outlet was located behind the condensing unit...but the point is that had a service tech not looked at the coil with a flashlight I never would have noticed the dirt.  Running water over the coil from a garden house to wash off the film dropped the system head pressure and restored the system's ability to maintain the thermostat setpoint without running non-stop.

Many years ago Louisiana State University conducted some tests on residential HVAC systems to determine the impact of dirty condensing coils.  The results were eye-opening.  A fine film of dirt, similar to what I had on my system, would reduce system capacity by up to 20%.  If your home, business, or server room is too hot then imagine what giving it an extra 20% of capacity could do...and it would only cost you a bit of water and time to wash off the coils...with no service tech assistance required.

Direct Evaporative Cooling Analysis for Two Diverse Climates

One of the common concerns expressed about the use of evaporative cooling for data centers, server rooms, telecom facilities, or other facilities housing heat producing electronics is the ability of evaporative cooling to achieve the target inlet conditions for the electronics.

These two psychrometric charts show the results of an actual analysis in two distinctly different climates.  The target server inlet temperatures were between 65 and 85 degrees F and between 20% and 80% RH.  The mechanical system criteria mandated that direct evaporative cooling be used.

The proposed mechanical system consisted of a direct evaporative cooling system with 12" cellulose media, a steam humidifier, DDC controls, and a hot aisle/outside air mixing section.  The controls would be configured to modulate the outside air dampers, hot aisle dampers, evap media water flow, and the humidifier to maintain the target conditions.

Server Inlet Temperatures from Evaporative Cooling System in Pacific Northwest US

Server Inlet Temperatures from Evaporative Cooling System in Southeastern US

As you can see from the charts the proposed system would easily achieve the desired results.  In fact, it was found that outside air cooling could achieve the targets during roughly 15% of the year, direct evaporative cooling could achieve the results during roughly 60% of the year, and remaining hours of the year when the air was too cold to properly operate the evaporative cooling without fear of freezing a combination of hot aisle and outside air supplemented with the humidifier would hit the target.  The only excursions of temperature over the maximum target of 85 degrees would occur for no more than 5 hours a year based on the NOAA TMY2 weather history.

While not every location would achieve these results the diversity of climate for these two studies imply that direct evaporative cooling, with creative use of mixing and controls, will work in many more climates than most people expect.  To further expand the capabilities of evaporative cooling an indirect evaporative cooling element could be provided to produce even broader temperature control.  Although it was not analyzed for this case we would expect that adding an indirect evaporative cooling element to these systems would have eliminated the few hours of excursion above the maximum dry bulb temperature.

As a means to dramatically reduce energy consumption for these data modules the evaporative cooling solutions such as those manufactured by the Aztec division of Mestek would prove to be extremely effective.  Since evaporative cooling systems are also relatively simple mechanical systems with no refrigerants maintenance of the systems does not require licensed refrigeration technicians and there are very few elements that could fail...increasing uptime and providing much faster recovery time should a repair be necessary.

Aztec Evaporative Cooling Solutions and the University of Texas at Arlington

On April 12, 2012 management and engineering representatives of Aztec, part of Mestex division of Mestek family of products, met with engineering representatives from the University of Texas at Arlington to define how resources will be jointly applied to researching and developing an advanced technology indirect evaporative cooling solution for data centers. Research already started at both organizations will be shared in order to more quickly advance the development of a viable solution to the high rate of energy and water consumption by data centers.

The joint project will be part of the NSF-I/UCRC program. This program, initiated by the National Science Foundation, is a collaboration between 5 major universities and a select group of industry contributors. The stated purpose of the program is to develop commercially viable solutions that will improve energy efficiency in data centers. Research projects range from chip level solutions all the way to complete, large scale, data center solutions. Aztec will be contributing special knowledge of evaporative cooling and outside air cooling solutions that has been developed over 40 years of product development and marketing.

Air Pollution and HVAC

Over the Christmas/New Years holiday break I was able to spend some time on the road crossing Texas, New Mexico, and parts of Arizona.  While I saw plenty of interesting sights it is not the goal of this blog to create a travel channel.  The goal is to highlight technologies and subjects of interest in the HVAC arena.

The subject that came to mind as I drove across these states was that of indoor air quality.  Two areas, in particular, raised my attention to this topic.  Phoenix, Arizona and El Paso, Texas were both covered with a thick layer of smog as I passed through those towns.  The climatic reasons are not all that relevant to this discussion but the "temperature inversions" that are common in those areas at certain times of the year mean that smog will develop and stay trapped for hours, if not days.  But those two cities are not alone.  Los Angeles, California has been well known for poor air quality for years.  New York City leaders have become concerned enough about outside air quality to include provisions in their new "Green Codes" that are intended to address the issue.  Finally, attention has been brought by the folks at NOAA to the fact that pollution in China eventually makes it way to the US on the jet stream.

HVAC products can either help mitigate this problem or simply move it from the outdoors to the indoors.  All buildings with occupants are required by building codes to have some amount of "ventilation air".  It has been common practice to introduce that ventilation air through conventional air handlers or packaged rooftop equipment.  In the vast majority of cases that equipment was designed, and is applied, with only the minimum level of air filtration included.  The primary goal of the filtration has been to protect the components of the equipment from dust fouling and to provide a nominal level of indoor air quality improvement.  New requirements and guidelines that specify MERV 11 and higher filtration are intended to let the equipment begin to mitigate the outdoor air quality before it enters the space.  But how effective is this?

In a conventional HVAC system design there will be dozens of these filters, if not hundreds, scattered all over the building in numerous air handlers or packaged units.  Maintaining all of these filters properly becomes an ongoing task.  In addition, if even better filtration is required, or desired, the average piece of HVAC equipment simply lacks the space to provide more filtration.

Dedicated Outdoor Air Systems, or "DOAS", equipment helps address this.  By isolating all of the ventilation air requirements into a single point, maintenance of the filtration system becomes much easier.  In addition, some "DOAS" equipment, such as the Applied Air FAP, is designed to allow multiple stages of filtration.  When combined with low airflow systems such as chilled beams the result can be very clean ventilation air even in areas such as those I drove through over the holidays.

As a final consideration for indoor air quality I would suggest that the old, ancient actually, technology of adiabatic or evaporative cooling might be considered.  Although adiabatic or evaporative cooling can provide effective temperature control in vast parts of the United States it can also provide an extremely effective filtering system as well.  Air is literally "washed" as it passes through the unit.  As part of an overall system where the adiabatic or evaporative cooling system, such as the Alton or Aztec products, only provides the ventilation air and other equipment handles sensible and latent cooling the improvement in indoor air quality could be dramatic.

Facebook Opens Data Center Design to the World

The big announcement in the information technology and data center world today was that Facebook has decided to make their data center and custom server designs open to the public to use in their own designs. This is a huge deal in that world since most data centers have more security than Fort Knox and even their exact location is often disguised. The most interesting part of this news is that Facebook is designing their centers with NO MECHANICAL COOLING. This furthers the trend among all the big players and is driven by the enormous energy consumption of these data centers. Data centers are little more than big warehouses but can have energy loads that exceed 600 watts per square foot.

According to the US EPA, data centers are responsible for some 4.5 billion dollars of electrical energy use annually. This represents 1.5% of all US electrical energy consumption and it is projected to double in the next five years. Shedding some of this enormous energy load is both environmentally and fiscally positive. It can also be essential to utility companies given the cost of building new generating capacity. While the economy is slowed this is not an issue but as the economy grows there might not be enough generating power to go around.

The growing shift to using outside air for cooling data centers has been accelerated by the changing design guidelines from ASHRAE and the server manufacturers themselves. It is now acceptable to operate a data center with air as warm as 86 degrees F entering the servers. Non-mission critical servers can now be operated with entering air temperatures up to 104 degrees F, according to the latest ASHRAE guidelines.

The Aztec and Alton lines of evaporative cooling products make excellent solutions for these buildings since they provide some level of cooling without the need for mechanical cooling. Data center owners get the best of both worlds...low energy use and filtered/tempered air for their servers. An Aztec indirect/direct evaporative cooling unit can supply air temperatures in the mid-60s to mid-70s in a broad part of the US. Aztec units are also “plug and play” units since they include an integral cooling tower. A data center can be brought on-line faster or expanded faster since the Aztec unit is a factory assembled and tested unit that can be set on the roof, or ground, and be up and running with a water and electrical connection.

Restaurant Energy Savings That Can Spread

For those who might have missed it there is an interesting Technical Feature in the March, 2011 issue of the ASHRAE Journal. The article deals with "Energy Savings for Quick Service Restaurants" but some of the research applies equally well to other applications.

The article covers several energy saving measures for restaurants and includes a section on the mechanical cooling. The recommendation of the writer is to combine the benefits of a DOAS unit with conventional rooftop packaged HVAC units to achieve a significant energy savings. This same savings can be found when this concept is applied to school classroom wings, small single-story office buildings, or any building where the "normal" HVAC solution would be a series of 10 to 15 ton rooftop units.

The writer suggests a system that has a DOAS unit conditioning the total ventilation air requirement for the building but putting the dehumidified and filtered outside air into the return air ductwork for several pieces of conventional rooftop equipment. This has the effect of both removing the latent load from the conventional equipment and lowering the return air temperature of the standard rooftop equipment. The result for the conventional equipment is that it can be downsized significantly.

Downsizing rooftop HVAC units from the 10 or 15 ton size down to a 5 or 7.5 ton size will not only reduce capital costs for the project as a whole but, in general, packaged HVAC equipment has a higher EER in smaller sized equipment. That is because it often begins to fall into equipment categories that are covered under Federal and State energy codes for residential applications. The "blended" EER of the total system could actually go up as a result.

That is one reason why it is important to look at the impact of design decisions on a holistic basis whenever possible.