Industrial Misting for Humidification

I occasionally have the opportunity to look at humidification applications where the customer wants to use high pressure misting systems.  I actually like working with these systems, they are simple, generally compact, affordable, and easy to install and service.  However, they are not the preferable technology for most humidification needs.  They work real well as evaporative cooling systems.  In fact, that is their drawback when applied as humidification.  The process of evaporating room temperature water, even atomized, takes a lot of BTUs from the environment, and thus cools as it humidifies.  This is perfect for the Southwest US in the dry summer.  But it can be problematic in most other industrial humidification situations.  The reason being that humidification is most needed when the air is dry, and in most cases that occurs in colder weather when the the contracted air doesn’t hold much moisture.  Misting systems, with their accompanying evaporative cooling will humidify the air, but they will cool it as well.  Which requires additional heated air, which is dry and soaks up the recently added vapor, etc….

I find it much better to use steam injection for humidification.  This of course has its problems as well, but technically is far superior as the moisture being absorbed is already at steam temperature and thus doesn’t require the loss of BTUs from the surroundings.  The problems mostly come in sourcing the steam for usage.  Injecting boiler steam is the easiest method, but it results in a loss of boiler capacity and some (albeit a slight amount) of water treatment chemicals.  An alternative to that is indirect, or steam-to-steam, systems that utilize heat exchangers to heat and inject a separate water source, thus saving on boiler capacity, boiler water, and treatment chemicals.  A bigger and more frequent problem is the lack of steam onsite altogether.  There are simply less and less building and utility systems utilizing steam.  This can be remedied with a small boiler or steam generation systems, or packaged humidifier systems.  Technically these are more efficient than misting systems in general.  However, the upfront costs are typically higher.  Up-selling to these systems can be difficult depending on the application and specific customer needs.

The typical industrial misting system consists of a high pressure pump @ 800-1200psig, feed lines, injection nozzles, and sometimes fans depending on the space and needs.  Some systems utilize stainless steel feed lines, typically mounted above worker spaces with injector nozzles at predetermined distances and no fans.  Others will utilize fans with nozzle rings face-mounted.  These systems are very applicable in high heat, low humidity environments, low worker-per-square-foot areas, and milder climates.  I have found several applications in flammable locations where low humidity causes static electricity and danger of explosions.  This has been a good technology for these applications and in low budget situations.

As in all things mechanical, applying these systems depends on an infinite number of variables.  While ultimately I prefer steam injection, high pressure misting is an acceptable alternative.

A New Reality, Yet Again

The folks over at Knowledge @ Wharton, The Wharton School of Business at The University of Pennsylvania have nailed a crucial aspect of the current economic crisis with an article on how it is inordinately tough on older managers.  The thing that is especially hard about this is that many of us, as we navigated the route to success or survival, found our way by specializing.  We went or were led into unique careers that increased our value.  The last twenty to thirty years has seen an unbelievable surge in managerial and technical specialization, and in independent consultants.  This has not been a case of foolish people following dead end paths.  It has been the prophetic invisible hand at work.  We did it because it made sense, intellectually and financially.  However, given America’s turn away from manufacturing, the global financial crisis, and the light-speed growth of technology, many of us are now at a disadvantage.  We are in a sense tradesmen with no place to ply said trade.

The impact for those of us closely tied to manufacturing is obvious.  But this downturn is not so selective.  It appears to be affecting everyone.  It not a select industry or specialty group that is feeling the brunt this go-round.  This is an equal opportunity recession.  It is affecting the banker and the backhoe operator, the engineer and the trucker.

You will notice my emphasis here is a human resources one.  I’m not even getting into the macro-economic side of this, although I am very interested in and equally confused by that.  What I am finding as a business owner is that it is not any easier than when I was an employee.  The bottom line is still the bottom line, still important, and still directly related to my paycheck.  I am like any of the other middle aged managers mentioned in the Wharton article.  I need to diversify, find other opportunities, make myself more valuable yet again.  The big challenge is, given the current environment, how do I go about that?

How indeed!

Steam Coil Freeze Protection

A major problem with heating with steam is the potential for coil freeze.  A necessary byproduct of steam is condensate, or water.  This is in theory a good thing as it indicates that the process is working.  As the heat from the steam is transferred to the medium, in this case airflow, the steam condenses back to water.  At this point it should be removed from the system via the steam trap, and in an ideal world this always happens.  However, we all know about the ideal world.

The typical freeze scenario comes into play because of system stall.  Conventional steam coil design utilizes a modulating valve to control steam flow.  Now, while I note this is conventional design, it is not necessarily optimal design.  In most cases of using steam in HVAC applications I recommend the Integral Face and Bypass Coil, as noted in a previous entry.  However, that design is not in itself always optimal, or always utilized; in which case the designer, plant engineer, or technician must deal with the situation at hand.  As it stands, conventional design utilizing a modulating valve will run into trouble at the point the valve begins to close as demand is satisfied.  If in this situation the valve closes so that downstream pressure is equal to or greater than upstream pressure the coil will be in a condition of stall.  The condensate will accumulate in the coil and is thus subject to freezing.

My choice solution for an existing conventional system is to utilize a freeze valve that will sense the water and remove it.  I use the Thermomegatech HAT valve with a setpoint of 100 Deg. F.  I install the valve in the condensate line between the coil and the strainer and/or steam trap.  I pipe the condensate to drain.  I have seen similar devices used by the steam specialty companies that were marginal or ineffective.  The primary reason being they had a setpoint in the area of 35 Deg. F.  This is too low and too close to freezing temperature.  The condensate may not be able to escape the coil before freezing.  On the other hand, having a setpoint of 100 F. seems to work well.  100 F. is way too cold for condensate, which should typically be over 210 Deg F., yet it is warm enough the condensate won’t freeze.

I have had positive results with this system.  While it is recommended for conventional steam heating, it can be applied in most applications where freezing condensate or system stall may be a problem.  Another problem with system stall outside of freezing is the introduction of air and non-condensables into the system through the vacuum breaker.  This is often seen in process heat exchangers utilizing modulating valves as discussed above.

The Handbook of Air Conditioning and Refrigeration, Free

Mohamed Fawzy has provided a link to a free download of this comprehensive and very large (1401 pages) book here:

HAC&R

Thanks, Mohamed!

Heating with Steam

I published an article in the March, 2005 issue of Engineered Systems Magazine entitled “Heating with Steam”.  Following is an excerpt with a link to the article in its entirety.

“Compared to hot water, there are several advantages to steam.  Due to higher energy content per mass, the required heat transfer area is smaller, heat coefficients are higher, distribution pipes and necessary plant sizes are smaller.  Rather than costly circulating pumps and the relatively larger components needed for hot water systems, steam is distributed and controlled through pressure differentials.  However, utilizing the heat of steam requires its condensing, which can be troublesome.  In fact, condensate and its removal are the source of most of the problems associated with steam heating.  To effectively take advantage of steam’s higher energy content and flexibility, the byproduct, condensate, must be controlled and utilized so as not to hamper heat transfer, or, worse, lead to frozen or damaged coils.”

Download the article in pdf here.

Enjoy.

The World of Industrial HVAC

Industrial HVAC is almost a misnomer in the US.  We have lost so much industry in our metamorphosis to a post-industrial society that there is less of a demand for our products and services.  As paper, textile, and steel mills close on our shores we all know that the chance of new ones being built is little-to-none.  We have found some degree of cross-over as we apply our technology and our products to institutional and healthcare settings.  And we are still maintaining some older plants.  But for the most part we are living in a new world.  The current recession has only made matters worse.

I am mainly stating the obvious here.  I am not decrying international trade, nor longing for the old days.  What we have is what we have.  The work ahead of us is focused on making proper use of what we have.  There are still uses for steam technologies, evaporative cooling, direct gas-fired make-up air, and process controls.  The challenge I think is re-imagining the world, seeing things differently.  If we continue to look at the world based on the way it was we will miss out on the way it will be.  That being said, I don’t have the answers.  But hopefully I have enough imagination and fortitude to find a way to make it all work out for me and my business.