How To Control / Dehumidify Indoor Air (IAQ, Climate Change, Power Grid and CO2)
Since it's the dead of Winter in Michigan (and its been pretty much raining most of it so far), and with Spring coming.... (maybe sooner than normal)......
Since its de-humidity season when it should have been the humidify season, I figured we might as well explore IAQ de-humidity style.
(There may also be good timing to this anyway, as we look forward to another record summer air conditioning style)
This is of course still an issue in the Southern states all winter long, and also in commercial and industrial settings.
When considering indoor air quality, on top of the list is humidity control.
Two main things to remember, sensible is the temperature (energy or heat) that can be measured with a thermometer, latent is the (energy or heat) tied up in humidity. It means hidden heat, and when it comes to condensing moisture from air, it takes lots of energy no matter which method is used.
Learn more about "Psychrometrics" here: http://en.wikipedia.org/wiki/Psychrometrics
Humidity out-of-control can result in structural damage, mold and mildew issues, and product loss or quality issues in manufacturing.
In the summer months especially, because of warmer outdoor temperatures, we concentrate our efforts on removing excess moisture.
The reason being warmer air holds more moisture than cool air, more moisture in the air can result in condensing on cool surfaces. You will see this in the interior of your refrigerator in humid climates, you will see outdoor hot humid air condense on the outside of windows in a COOL air conditioned house, you will see this inside your walls in the winter if interior moisture (from bathrooms and kitchens for example) gets into the wall and interacts with the cold drafts of winter.
As far as indoor air quality, and removing the moisture, there are three basic ways to do it. One easy way (sort of) and two better ways - although the two better ways are rarely seen in the residential and light commercial markets (they are not simple).
Most of the time, moisture is removed by condensing it on a cooling coil either in a residential furnace, or in a rooftop or air handler of a commercial application. The refrigeration system makes the evaporator coil cold, the moisture is condensed on the coil, and then drips off and runs to a drain.
Link to more details on refrigeration cycle humidity removal: http://www.aireserv.com/expert/split_system.aspx
The unique and somewhat disadvantageous part of this method is the cooling coil / refrigeration system is also the method of temperature control. When its warm in the space, the system runs, the water is removed, the air is cooled, the temperature is brought down to the desired level.
Then the refrigeration shuts off, either by way of a control valve or the compressor cycles off all together - varying degrees of both depending on load.
The problem is if the space temperature is cool enough such that the system doesn't run, the coil is thus warmed up to the airstream temperature and not cool enough to condense any moisture from the air. NO dehumidifying.
There may well be times when the temp is OK, but yet the humidity is elevated - but the system will be ineffective at this condition.
Think in terms of a commercial laundry with steam and water driven processes (although also a warm situation), consider an indoor swimming pool, or any other application with a high indoor humidity load. Also consider an application with any appreciable outdoor ventilation air requirement, during which case humid outdoor air (normally warm) is brought into the cooler indoor environment.
Another, better method of removing moisture is the dry desiccant wheel. Although complicated from a mechanical system, psychrometrics, and control standpoint, they are actually fairly simple devices.
Think in terms of the little desiccant pack you find in a new box of shoes, basically a chemical pellet or other form of media absorbs moisture via a chemical interaction with the moist air.
A chemical embedded wheel rotates in and out of the air stream, moisture is absorbed from the air and captured in the "desiccant material", and as the wheel rotates to a second exhaust air stream, the wheel is heated which in turn evaporates the moisture from the wheel and then blown out the exhaust stack to the outside. Simple. But energy intensive.
Link to reference source with more details: http://www.energysolutionscenter.org/tech/tech_desiccant.asp and http://www.muntersamerica.com/
A third and less common, but also more interesting system is the liquid desiccant system. Nearly identical in method as the above wheel, the difference is the moisture absorbing material is actually a water / mineral salt fluid. Yes, mineral water will absorb moisture when sprayed into the air stream. As long as the mineral is Lithium Chloride at about a 40% solution.
The solution is sprayed in the air stream in the "conditioner" section, captured in a basin, then pumped to the "regenerator" section where it is heated and the moisture driven off and out via an exhaust fan (out the roof).
More on liquid desiccant systems here: http://www.kathabar.com/
Simple, but also complicated. These systems will be found in extreme industrial applications like candy factories, pharmaceutical and other demanding applications. History note, they have their roots back in the Manhattan Project.
Why does this all matter?
When it comes to climate change, warmer outdoor temperatures mean higher humidity loads on mechanical systems - we have to remember the humidity is removed first before any cooling can happen. NO COOLING if the system is overloaded because of elevated temperature and humidity.
The air conditioning load from millions of residential commercial and industrial buildings is a major load on the electric grid, which means power plants, which means CO2 emissions.
Are you ready to go without your air condition? Are you ecologically minded, but what about during a heat wave?
Should we shut down offices and factories?
In California the new "Demand Response" laws will require customers on the grid to "willingly submit" to controlled air conditioning outages if the grid gets overloaded or unstable - this a stop gap measure to prevent rolling black outs.
Now with the new CO2 / Sustainable measures in California, the day may come where air conditioning is considered a luxury and your government might say no more?
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Air Conditioning | CO2 | Energy | IAQ | Kyoto | Sustainability
Additional problems
Submitted by mole333 on 7 January 2007 - 9:52am.
Mold means illness for some. In my building we already have had black mold problems leading to ACs needing replacement (yes...AC units are a major breeding ground for this potentially deadly mold) and walls being dismantled, treated and repaired. As this problem spreads with higher humidity, AC replacement will have to happen much more often as they become infested with mold. Maintenance of buildings will also go up because you can't kill this mold with household cleaners. Believe me. I know.
Higher temperatures and humidity means increasing tropical diseases in temperate zones, something that has already begun. Let's not forget that the US used to be a major malaria zone. Will that return? It is possible. West Nile is spreading. Etc. Here we are more in my expertise, and I can tell you that the US is not prepared for the spread of these diseases. Not only is our healthcare system already showing cracks, but we are already having trouble keeping our antibiotic arsenal ahead of evolving bacteria. Increase the population of bacteria (and if we continue our misuse of antibiotics in agriculture) we will see more rapid evolution of resistent bacteria. We are not ready for this.
Higher temperatures and humidity also mean increased insect populations. I predict next year will be a majorly bad insect (including mosquito) year will happen next year in much of the US due to the limited winter. We will have more and more years like this.
Multivariable equation. We can't focus on just two of the variables. We need to focus on all variables...including the dominant one which is the rising temperature.
Help! Replacing my AC right now
Submitted by JJ Ross on 7 January 2007 - 12:57pm.
Could I trouble you guys for a personal question about this?
I am right where you describe it, at this moment in the South on a very humid day but of mild temperature (everything is damp and sticky, so much so that yesterday I turned off the heat and switched to AC out of desperation) -- we are TOMORROW signing the contract to replace our aging and ineffienct home system and I would dearly love your advice, hoping to avoid the purchase of something that would instantly obsolesce or do uneeded harm, or run up our operating costs. With or without brand names is fine, but what we're looking at is a new-tech-type SEER 17.5 to 19 two-condenser heat pump with a matched variable speed air handler (using the new coolant that supposedly isn't being phased out with the bad old freon, I forget the numerical designation, 42-something?) and the superduper electronic air cleaner.
Help! It's many thousands of dollars and feeling like an enemy of the environment if we stupidly screw this up. I am very bright and I've done my online research at the various consumer websites but I'm NOT technically expert in any scientific field, least of all this one. Thanks in advance, JJ
Not sure
Submitted by SteamGeek on 7 January 2007 - 8:52pm.
There are pros and cons no matter what choice you make. The electronic air filter will use electric energy to function, as would a HEPA also drive up system static which means increased fan energy - both options that way use more energy. In this area (as others) if it were me I would follow the KISS method and and simply go with a good quality traditional filter. This keeps front end costs down, keeps ongoing energy costs down, avoids bothersome ongoing electronic filter cleaning, avoids costly HEPA replacement. IF there are family health issues such as allergy or other respiratory illness or immune sensitivity then everything I said is out the window and the priorities shift back to the high performance / cost choices. This might be an area where once you have chosen a service contractor you trust, go with their advice - but hold them accountable after the sale. The last word in this is also talk to someone who already has the system you are considering, word of mouth is the best marketing.
As far as the actual refrigeration system, keep in mind with any evaporative based cooling system (see split cycle above) if the temp cooling isn't called for at the stat, the compressor isn't running and there is no dehumidification. This is where region to region psychometric analysis needs to be done for proper system selection.
Desiccant dehumidification systems are very energy intensive.
The bottom line is residential humidity control (removal) is very difficult to do and architectural and exhaust fans use are in my book the best way to address it, not at the central system.
As far as heat pumps, ground coupled closed loop are the ones I'm familiar with, what ever system you go with pay close attention to qualifications and references of the service contractor, and again talk to folks with installed systems for independent reference.
I'm not a fan of paying extra for un-needed bells and whistles, yet paying a fair price for a modern energy efficient system is goal for all of us. That balance is of course the tough part.
The links I provide in my post's are all excellent research resources, if you want additional let me know.
One last thing to consider is mold, it can be a serious issue as Mole333 indicates. Many times mold is an architectural issue with poor vapor barriers, and infiltration via windows doors and other envelope issues. Secondary internal moisture loads are easily mitigated with proper use of exhaust fans in the bathroom and kitchen.
When I speak in the post about grid issues with humidity control I'm speaking primarily to commercial structures where code mandates a certain minimum quantity of outdoor air brought in for IAQ ventilation purposes - in other words CO2 and other contaminant control (CO2 is a common IAQ contaminant that comes from human respiration).
ASHRAE standards are the best resource to understand this, but the point is that current conditions are taxing the electric grid, and none of the politician or environmental lobby CO2 conversation is going to have any positive impact for easily hundreds of years as far as I'm concerned, so we need to sharpen our pencils and begin to think about modernizing our generating capacity like a national emergency starting now. The only two feasible ways to generate large quantity megawatts are via traditional fossil fuel and nuclear. As the heat is rising in the major AC regions now, as our grid is pretty much in the process of collapsing now, as our plants are all significantly aged now, the CO2 politics may be the least thing we should be worried about.
(coreection added, many plants are aged now)
Absent a stable grid, we could easily see European style problems with our aged population if we fail to maintain our AC.
I'm not in the marketing side of the business so I have nothing to gain by pushing this issue. Actually I'm the guy folks call when things go wrong, I wouldn't mind if the phone rang less often.
Air Conditioning
Submitted by Elboydny on 12 January 2007 - 1:50pm.
An air system is the only way to go and air conditioning is important to the long-term durability of your home. Air conditioning can add heat, moisture and humidity to the air of your home. You should know what size air conditioning system is needed. Some air conditioning units are generally quiet enough to be installed under a window or near a patio, so sleeping or the entertaining of guests is not disrupted. Centralized air systems are in the vast majority of "newer" homes.
European Heat Waves / US AC needs
The US South, Southwest and West are well known as major Baby Boomer retirement shifts in demographics.
These regions have unusually strong voting influence in national elections, and also are particularly vulnerable to temperature increases and the resultant humidity increases that tax the air conditioning equipment. The problem is that to the extent these major populations are also aged, they are also vulnerable to air conditioning failures and the resultant health consequences.
Culturally, the Europeans do not have the extensive built out air conditioned building base we have in the US.
When we consider recent major European heat waves, the lack of air conditioning was attributed as a factor in the significant loss of life.
It would seem the needs of society during heat waves, the resultant additional load on the electric grid, and the CO2 reduction conversation are competing with each other with no easy solutions.
For more research, here are two basic places to start:
http://en.wikipedia.org/wiki/European_Heat_Wave_of_2003
http://en.wikipedia.org/wiki/European_heat_wave_of_2006
Once folks are willing to connect CO2 conversations with Electric Grid needs, and consider human health consequences if we fail to maintain the grid, we also have to take a very close look at what we know about the Atlantic Gulf Stream and potential consequences if the Gulf Stream falters.
I for one am curious which way the coin flips when we consider long term heating or cooling trends.
I think the 2003 / 2006 European experience, coupled with our own Southern and Western population demographics illustrates the very sensitive nature of the problem.