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Humidification

mel rowe
mel rowe Member Posts: 324
Previously posted this on the A/C site, with no response, so thought I'd try it here. --------
Been trying for some time to get adequate humidity in an old house that has steam heat. Have installed an air handler and necessary duct to reach most of the rooms. Contractor said I would have to use a steam humidifier to get enough moisture into the air, which is of course at room temperature. After suffering with very expensive operating cost and big problems with calcium buildup that requires too frequent cleaning, I'm looking for alternatives. What I'm trying to figure out is whether using a conventional flow through type of humidifier (or even two)could put enough moisture into the air stream to do the job for me. No one at Honeywell was willing to estimate how much water I could evaporate in 24 hours, with an air flow of 650 cfm, and air temp. of 70 degrees. I'd greatly appreciate any ideas, or input on this subject.

Comments

  • Dan Foley
    Dan Foley Member Posts: 1,258
  • JimGPE_21
    JimGPE_21 Member Posts: 9
    Wow.

    This particular quest is not for the faint of heart.

    First of all, do you have any type of technical background - are you in the HVAC field, for instance, and more importantly, do you know what a psychrometric chart is?

    No disrespect intended - I just need to know how technical I can get with the answer.

    Beyond that, what relative humidity do you want to hold, and how important is it that you get to that level? Health issues? Problems with wood cracking? What is driving the desire to increase relative humidity?

    Does the house have single-pane windows? Any insulation in the walls? What do you know about the vapor barrier in the walls?

    During your efforts to humidify thus far, have the windows or walls ever sweated?

    Jim.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Your humidity rate of introduction

    is principally a function of your space or incoming relative and specific humidity, Mel.

    If the space is dry you will evaporate more and as it comes close to equilibrium, less. Heating the water (weather to steam or just above ambient) increases evaporation as does increasing the air temperature. Doing that increases the ability of air to hold humidity. Trying to humidify with isothermic air is entirely dependent on the dryness of the incoming air. It starts out picking up what it can then drops off. No way to force the issue without heating the air or heating the water or spraying the moisture (atomizing it) to increase surface area and evaporation potential. Can you put in a heating coil?

    Your 650 CFM works out to about 48 lbs. of air per hour. I am not sure how you arrived at that figure or what the overall volume is you seek to condition to what % RH.

    If the air is at 20% RH to start, it will be holding 22 grains per lb. If that same air can absorb to equilibrium at 30 percent RH (33 grains per lb.) the difference is 11 grains per lb. This works out to 0.07 lbs. of moisture per hour. Diddly, especially when applied to an unknown volume of space with unknown infiltration and diffusion rates.

    If you could saturate that 650 cfm (70 degrees and 100% RH) it could carry 110 grains per lb. Delta-Grains =88. This works out to 0.60 lbs. per hour, a little more than half a pint per hour to be diffused into what volume I do not know. If you could heat the air to 90 degrees it could carry over 200 grains per lb. at saturation.

    As for types of humidifiers, wetted pads seem to be simplest as do rotary wheel types but you have that standing water issue. If water quality is an issue I would stay away from the ultrasonic types. Mineral dust is deposited everywhere.
  • mel rowe
    mel rowe Member Posts: 324


    Thanks very much for the replies. I'll try to give more info this time. Since I have one pipe steam heat, I've had to resort to adding a separate system for A/C. The house has always been dry like a desert. In my desperation to get enough humidity, I had another air handler installed in the basement and tied into the a/c system, and a humidifier installed. The humidifier that was installed is a Honeywell 440A unit, 110v, 1500 watts. In my 3 years of experience, I've found that all my added insulation in walls and attic, plus thermopane windows, has gotten me to where the humidity will hold at recommended levels, except when the temp. here in Mich. goes down to 10 degrees or less. Then it's capacity becomes borderline. I can live with this condition; however, running this unit 24/7 costs me about $95/mo. In addition, I'm constantly having to clean out deposits (which is very difficult and time consuming), in order to keep it running right. In adddition, the two filters required are very expensive. So that's the reasons I'm pondering if there are better alternatives. This unit is rated at about 11 gal/day, so I'm wondering if evaporative humidifier(s) running with the house air temp. of 70 degrees might achieve the necessary level of water evaporation without the cost and hassle. By the way, I'm not a HVAC guy, just a retired engineer willing to tackle whatever I can work on around the house. Thanks again.
  • Mark Hunt
    Mark Hunt Member Posts: 4,909
    Humidity

    Mel,

    Humidity levels in ANY home are directly attributable to the amount of air leakage in the building. This is called "stack effect".

    Warm air will leave a building near the top and cooler/drier air enters at the bottom. The cool/dry air then grabs heat from the building AND moisture. As it heats it rises and leaves the building. The more leaky the home, the drier it will be in the winter months. Humidifiers are really just a band-aid.

    See if you can find an insulating contractor in your area that can perform a blower door test and offer solutions for reducing the air leakage. Not only will this help alleviate the dryness, it will save you money on your heating bill as well.

    Mark H

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  • JimGPE_21
    JimGPE_21 Member Posts: 9
    You can have too much humidity

    You need to be careful in an older home especially that all the humidity you are producing is not condensing inside your walls and on your windows. This will cause MAJOR problems.

    Between your indoor conditions and 10F outside, there is a surface that is below the dewpoint of the air. That material that is below the dewpoint will sweat like your ice tea glass in the summer. Just be carefull you don't pump too much moisture into your home. At 10F outside 20% relative humidity might be as much as you can get.

    There's probably a graph that came with your humidifier that shows maximum indoor humidity v. outdoor temperature for a typical home construction. This is the basis of that chart, and you ignore it at your own risk.

    Jim.
  • mel rowe
    mel rowe Member Posts: 324


    At this point I'm satisfied with the level of humidity I can maintain with my current steam unit and I try to follow the recommended levels on charts such as mentioned. If it gets too high, I see it immediately as condensation on the windows, because my one pipe steam radiators are not situated at every window, and some of them stay cooler than others. I'm just looking for advice as to whether it may be possible to change over my system from steam humidifier to regular (evaporative type) humidifier and still be able to get adequate moisture into the air stream. Remember that I'm using room temp. air and flowing at 650 cfm through the system. My current steam unit is rated at 11 gal./day. If this is possible it would greatly reduce my operating cost and avoid many other problems with the steam unit. Thanks.
  • CHARLES_4
    CHARLES_4 Member Posts: 61
    HUMIDITY LEVELS

    Too bad you don't have radiator cabinets/covers. If you did, you could place a water tray on top of each radiator and get some free humidity. Have you considered a fish tank?
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Covers not necessary

    A pan on top will do just nicely. Copper is great because it is naturally anti-fungal.

    Personally I have considered a fish tank but when place on the radiators, the fish objected :)
  • CHARLES_4
    CHARLES_4 Member Posts: 61


    Get tropical fish...
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    A-ha!

    LOL!
  • Rely_2
    Rely_2 Member Posts: 61
    Hydronic coil

    add a hydronic coil to the airhandler and sup the steam system with the air hanler. from what I'VE READ your operating cost is 95 a month you could raise air temp in air handler and add more humidy this way but you would have to do some pipe work on the boiler does the boiler have a domestic coil and maintain temp?

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  • Cosmo_3
    Cosmo_3 Member Posts: 845
    great idea

    Keep an empty fish tank on the radiator, when hungry throw in a lobster, or you can make eggs benedict, or......


    Cosmo Valavanis

    Dependable P.H.C. Inc.
  • Rely_2
    Rely_2 Member Posts: 61
    What is

    Making your domestic hot water? If it is a oil fired hot water heater you could still add hydronic coil and use a tace sr 503 exp control with pump exersizer aand control system with humidistat

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  • Brent_2
    Brent_2 Member Posts: 81
    humidity

    I think a standard Aprilaire 700 is rated at 0.5 gal/hr for 90° air. You can check the exact numbers on their site. If you run it all day you get 12 gal a day. Since you will have 70° air you will get a little lower. They are a lot less work and expense then what you are dealing with. Depending on your setup maybe you could use an aprilaire most of the year and then use both during the coldest weather. You could also look into getting a stand alone humidifier to place in your bedroom (or whereever you need more humidity.

    Brent
  • mel rowe
    mel rowe Member Posts: 324


    After reviewing all the good comments (other than a tropical fish tank over the radiator ----LOL) and looking through a lot of info on evaporative type humidifiers, it appears that the best potential unit for my plenum size, etc, may be the Aprilaire 600. The company claims it will evaporate .7 gal/hr., with my 650 cfm of air flow. The only kicker is that it requires a flow of hot water of 3 gal. per hour to provide enough heat to assure this level of evaporation. I realize this is wasteful of water and energy, but compared to the cost of operating my current steam unit, it's peanuts. Plus I can cut back on the water flow and see what results I can get. Would appreciate comments on this approach.
  • mel rowe
    mel rowe Member Posts: 324


    After reviewing all the good comments (other than a tropical fish tank over the radiator ----LOL) and looking through a lot of info on evaporative type humidifiers, it appears that the best potential unit for my plenum size, etc, may be the Aprilaire 600. The company claims it will evaporate .7 gal/hr., with my 650 cfm of air flow. The only kicker is that it requires a flow of hot water of 3 gal. per hour to provide enough heat to assure this level of evaporation. I realize this is wasteful of water and energy, but compared to the cost of operating my current steam unit, it's peanuts. Plus I can cut back on the water flow and see what results I can get. Would appreciate comments on this approach.
  • Steve Garson_2
    Steve Garson_2 Member Posts: 708


    How big is your house? I have around 2700 square feet in Boston that I humidify with a console humidifer with evaporative pads. I fill the two portable tanks every four or five days and the house stays at a comfortable 30% - 35% humidity, unless I get lazy and don't refill.

    I've used the same system for ten years, changing the filter pads twice each heating season and using bleach to clean the surfaces every six weeks or so.
    Steve from Denver, CO
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