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Old 10-16-12, 12:15 AM   #1
ecomodded
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Default Heat house with dehumidifier

I have found some good info on heating your house with a dehumidifier, as it turns out a dehumidifier is 150% efficient when it comes to making heat.
Also,as it turns out i have one and am using it now, for heat.

Heat your home with a dehumidifier | IWillTry.org

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Old 10-16-12, 09:36 AM   #2
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I'm going to disagree with that article all together.

Heat pumps (like a dehumidifier) move heat, that is all they do. A dehumidifier takes heat out of the air/water so the water condenses and seperates from the air. So, you're taking heat out of the air in your house. Now, to do that it moves that heat where? Well, it stays in your house. So, you're taking the heat out of the water and dumping it, but that heat was in the house to begin with. So, you really don't gain anything from it.

If everything were 100% efficient your net gain would be a loss in heat because the water still has some heat energy in it and you're dumping that down a drain. However, the dehumidifier is not 100% efficient at its process and thus creates waste heat. So, in all likelyhood you do have a net gain in heat, but its not going to be a 100% efficient process like just using an electric heating element because you're doing other things with that electricity (pumping heat around to condense water).

The other thing to add is in some homes that are leaky (which is probably the majority of homes), you probably want to add humidity to the house. Higher humidity increases the comfortability of the house and allows you to lower the temperature, but still feel like the temperature is higher. See this thread: http://ecorenovator.org/forum/renova...mperature.html
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Old 10-16-12, 10:15 AM   #3
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The heat is there much the same as a piece of fire wood waiting to be burned, there is no heat until it is created threw a process.

enthalpy

There is a property of any substance known as the enthalpy of vaporization. “Enthalpy” really just means energy. The enthalpy of vaporization of a substance is a measure of how much energy it takes to convert a given mass of the substance from a liquid to a gas. It also indicates how much energy is released when a given mass of the substance is condensed from a gas to a liquid. The enthalpy of vaporization of water is 2257 kJ/kg.
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Old 10-16-12, 11:53 AM   #4
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My dehumidifier collected 3L of water in 8 1/2 hrs.
Which brings the heat generated percentage up to around 175% as compared to a baseboard heater, using the math the Author of the article wrote.

Due too the excessive noise i am going to run it in the Dinning room, over the night.
If this guys math and science is correct it appears to be an effective way to save on heating costs.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

from the referenced article.

a dehumidifier is MORE efficient than an ordinary electric heater, which is already 100% efficient. Yes, a dehumidifier is more than 100% efficient at heating your home. That is to say the amount of heat a dehumidifier will release into your home is greater than the amount of electrical energy it will consume. The reason is simple: a dehumidifier removes energy from water vapor in the air in order to condense it to a liquid. This energy is released into your home.
It’s all about enthalpy

There is a property of any substance known as the enthalpy of vaporization. “Enthalpy” really just means energy. The enthalpy of vaporization of a substance is a measure of how much energy it takes to convert a given mass of the substance from a liquid to a gas. It also indicates how much energy is released when a given mass of the substance is condensed from a gas to a liquid. The enthalpy of vaporization of water is 2257 kJ/kg.
What is the efficiency?

How efficient is a dehumidifier at heating your home? Let’s figure it out together. I mean that literally. As I write this, I haven’t actually figured it out yet myself. I’m flying by the seat of my pants here, people; I’m a scientist gone rogue. But luckily I’m also a scientist who recently acquired a portable dehumidifier. I plugged it into a Kill-A-Watt meter several hours ago to measure exactly how much electrical energy (indicated in kWh by the Kill-A-Watt meter) it consumed. It’s been running for about 8 hours and it has consumed 3.87 kWh of electricity. Thus, based on the first law of thermodynamics I know it has put at least 3.87 kWh of heat into my home.

However I have also determined with a simple digital scale that it has condensed 3.23 kg of water in that same time. How much additional energy did it release into my home as a result of that? That’s where the enthalpy of vaporization comes in. 3.23 kg multiplied by the enthalpy of vaporization of water (2257 kJ/kg) gives 7290 kJ of energy. A kWh is equivalent to 3600 kJ so 7290 kJ is equivalent to 2.025 kWh.

Thus, the total amount of heat released into my home by the dehumidifier over the last 8 hours is equivalent to the 3.87 kWh of electricity consumed, plus the 2.025 kWh of energy released by the condensation of water. The “efficiency” is equal to the energy output divided by the energy input or in this case (3.87 + 2.025)/3.87 = 1.52 or 152% efficiency. An efficiency over 100% is more appropriately referred to as a “coefficient of performance” since technically, it is impossible to achieve greater than 100% efficiency (having more than 100% efficiency in energy conversion would defy the first law of thermodynamics). So if you ever measure more than 100% efficiency, as I just did, what it really means is that you have moved energy from one place to another rather than simply converted energy from one form to another. Such is the case with a dehumidifier which removes energy from water vapor and releases it into the home in the form of heat, condensing the water to liquid in the process. But whatever the terminology you want to use, the fact remains that I can release 1.52 kWh of heat into my home for every 1 kWh of electricity my dehumidifier consumes.
What’s the payback time?

I paid about $250 CAD for my dehumidifier. It consumes about 480W of electricity (3.87 kWh in 8 h) and outputs about 730W of heat (480W*1.52) into my home. I can buy a decent electric heater that will output 730W for about $50. So the difference in price is about $200. Let’s calculate the difference in the cost to operate. A 730W electric heater consumes exactly 730W of electricity. The dehumidifier only consumes 480W of electricity to produce the same 730W of heat. The difference (730-480) is 250W. Effectively I get a free kWh (1000 Wh)of heat for every 4 hours of operation. I currently pay about $0.07 per kWh for electricity, so I save about $0.42 per day when operating the dehumidifier in place of a heater. My heating season runs from October through March, or around 180 days of the year. Therefore, I can save about 180*$0.42 = $75 per year by operating the dehumidifier in place of a heater. That will take a little over 2.5 years to pay back the difference in price of $200.
Will this work for anyone?

In a word, “No”. The human body is most comfortable at a relative humidity between 20% and 60%. I can run my dehumidifier continuously in winter and not expect to ever drop below 20% relative humidity inside my home. The same may not be true for homeowners in other locations maintaining their homes at higher temperatures than I do. Heating with a dehumidifier works for me because of the high relative humidity in Richmond, even in the winter, and because of the low temperature at which I keep the interior of my home. It could work well for anyone who lives in a similar environment and keeps their home at a low temperature. But if you live where temperatures are usually below 0 degrees C outside in winter then you likely have a much lower relatively humidity. In that case, a dehumidifier will not be able to condense nearly as much water for a given amount of input energy and its operation may bring the relative humidity below a comfortable level.
Clothes dryer vs a rack and a dehumidifier

If you’re considering hanging your wet clothing to dry inside your home, vs using your drier, then you should know that a dehumidifier will be far more efficient than a clothes dryer. In the case of a clothes dryer, electrical energy is used to vaporize the water in your clothing and the water vapor (and all the energy you’ve put into it) is expelled from your home through your drier vent. There is a net loss of energy from your home. If instead you use a dehumidifier, the heat already in your home is used to vaporize (evaporate) the water in your clothing. This energy is recaptured by the dehumidifier when the water vapor is condensed to liquid. Unlike the drier, the dehumidifier doesn’t expel any energy from your home.
Heat pump vs dehumidifier

A dehumidifier is effectively a heat pump. Rather than extracting heat from the ground or the outside air, a dehumidifier extracts heat from water vapor contained in a home’s inside air. In my home, for reasons given above, I can run my dehumidifier continuously without reducing the relative humidity in my home below a comfortable level and I’ve found the coefficient of performance (COP) is about 1.52. A typical air source heat pump has a COP of around 4 assuming an outside temperature of around 0 degrees C (a typical Richmond winter). A typical ground source heat pump has a COP of around 7 assuming a ground temperature of around 10 degrees C (a typical Richmond ground temperature). So clearly, a heat pump (either air or ground source) is much more efficient. If I had a heat pump, I would be consuming more energy than otherwise by operating my dehumidifier. That said, I feel secure in the knowledge that I can run my single dehumidifier continuously and consume less energy to heat my home than if I were running an electric heater. I’ll save the installation of a heat pump for another day… perhaps.
Can you heat your whole home this way?

No. If I were to install more portable dehumidifiers to provide all the heat my home requires (to maintain a balmy 16 degrees C all winter long) I would almost certainly bring the relative humidity below comfortable levels, and the COP would drop below the measured value of 1.52 simply because there isn’t enough water vapor in the air to be condensed. So the idea of using a dehumidifier to heat one’s home is clearly not scalable. At best a dehumidifier may provide supplemental heat. I think I might get away with using two portable dehumidifiers continuously which would each save me about $75 per year based on the calculations above. That’s about $150 per year in total. Currently, that’s about 10% of my home’s annual heating bill.

Last edited by ecomodded; 10-16-12 at 11:57 AM..
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Old 10-16-12, 03:02 PM   #5
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Every degree C that you can pull out of that 3 liters of water is going to give you 3.5 watt hours of heat/energy and I was told that a rough rule of thumb is that to go that last step from liquid to gas that water needs 5 times the energy input to make that last step, so going from 15C (60F) to -0-C (32F) you have a 15c drop or 52.5 watt hours of heat in that water, cooling it that first degree to get it to turn from gas to liquid fallow the rule of thumb that I was taught gives you an extra 17.5 watt hours or 70 watt hours total of extra heat out of Ecomodded's dehumidifier, that is, if you can cool that moisture down to just above freezing before dumping it down the drain, collecting that water over the course 8.5 hours... electrical draw from my dehumidifier is around 300 watts averaged out when running constant (compressor cycles on it kicks up to 600+ watts) so over the course of 8.5 hours it draws 2550 watt hours and you can get an extra 70 watt hours of heat out of the unit... that seems more along the lines of what I have seen!
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Old 10-16-12, 03:06 PM   #6
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I see where he is getting the heat from the conversion of water vapor into water. That makes sense. However, the energy to do that must come from somewhere. The energy is going to come from the dehumidifier.

This is the statement that is incorrect.

Quote:
Itís been running for about 8 hours and it has consumed 3.87 kWh of electricity. Thus, based on the first law of thermodynamics I know it has put at least 3.87 kWh of heat into my home.
While he has used 3.87 kWh, not all of that is turned to heat. Some of it is running a motor for the compressor, some of it is pumping fluid through the heat pump system, some of it is being lost as heat energy. So, only a portion of that 3.87 kWh is being returned as heat energy. The rest is doing actual work and converting the energy from the phase change of water. There is no other source of energy to do it.
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Old 10-16-12, 04:35 PM   #7
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@Ryland , from your findings it appears the enthalpy of condensation has moved the dehumidifiers heating efficiency number to about 103% as compared to a baseboards efficiency.
I took a temperature reading from my dehumidifiers exhaust , it was 13 F higher then room temp, despite the high airflow from the fan, it gave me the impression it was working very well as a heater being it only uses 500 watts at peak.
To measure BTU's created would I x airflow by temperature increase ?

Doax, i now see that he (the Author) forgot to add 'work done' into his equation, 'work done' by compressor & fan, that was not turned into heat.
We know how inefficient a gasoline engine is where a large amount of energy is turned into waste heat threw the exhaust and radiator.
How would one find the losses too heat from the compressor and condenser ?
I suspect it is very high , 90+% as it is a heat pump of type.


Heat added, minus ,work done.
We have two heat sources, condensation and mechanical
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Old 10-16-12, 06:14 PM   #8
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Default 1kw of enegy into 2.5kw

This next dehumidifier must be very, very efficient.
Or is it fudged marketing ?

Calorex dehumidifier.
How does a Calorex Dehumidifier work

Due to the unique nature of a refrigeration circuit, energy removed from the air during the dehumidification process is converted into useable heat. Typically, for every 1kW of Electrical energy that a dehumidifier consumes, it will give out 2.5kW of heat energy. Thus by removing moisture from the air, rather than heating it to a high temperature, Calorex dehumidifiers will dry in a gentle, more controllable manner. This alleviates possible material shrinkage and cracking problems associated with high temperature drying methods and saves substantial running costs.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Industrial Dehumidification - Acker & Associates

In the pdf file about 4 pages down next to the section, 'Large Industrial Dehumidifiers' there is a diagram called under Process air analysis you can see the Btu per hr, for sensible and latent Btu's ,the latent is higher then the sensible, which i found odd, it must be indicative of that system.
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Old 10-16-12, 11:52 PM   #9
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I found another pdf file which shows their dehumidifiers are making more then twice the heat energy then they consume while making it. Sounds like hogwash, i admit, but it seems to be true.

This appears to be a real phenomenon caused by the condensation process, Not just bad math.

Page 13 has charts of interest when it comes to performance.
http://www.hidros.eu/materiali/downloads/114413088.pdf
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Old 10-17-12, 11:01 AM   #10
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That 13F rise in temperature is from the energy being used, the dehumidifier is in a closed environment! all of it's energy gets turned in to heat in the end.

Something else important to remember is that dry air feels cooler then damp air, old saying "It's not the heat, it's the humidity!" holds true and is part of why when heating with wood stoves (a dry heat) putting a pan of water on the stove makes the space feel even warmer, while in the summer I can take my dehumidifier and place it in my hot humid room to dry out the air and it might raise the temperature by 2 degrees but it will also lower the humidity by 40% and make that slightly warmer but dry room feel cooler in the summer.


Last edited by Ryland; 10-17-12 at 11:05 AM..
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