Comments on: Heat your home with a dehumidifier http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/ Climate change is real. You're causing it. You can stop it. Will you try? Wed, 01 Feb 2012 12:51:02 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Rob http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-9030 Rob Thu, 26 Jan 2012 07:24:05 +0000 http://www.iwilltry.org/b/?p=384#comment-9030 @ JohnC, I appreciate your persistence. But compare the two scenarios: 1. Without dehumidifier: cool moist air enters the home and room temperature moist air exits the home. 2. With dehumidifier: cool moist air enters the home and room temperature dry air plus liquid water exits the home. In both scenarios the air and water vapor coming into the home contain the same amount of energy (I think we agree on that). But in Scenario 2, the air and liquid water exiting the home contain less energy than the air and water vapor exiting the home in Scenario 1 (I'm not sure we agree on that... if not, look up "enthalpy of condensation" in wikipedia). Since Scenario 2 has less energy loss from the home, where do you suppose the "saved" energy goes? The first law of thermodynamics says energy must be conserved. The answer is that the energy (the enthalpy of condensation) is released inside the home in the form of heat. @ JohnC, I appreciate your persistence. But compare the two scenarios:

1. Without dehumidifier: cool moist air enters the home and room temperature moist air exits the home.

2. With dehumidifier: cool moist air enters the home and room temperature dry air plus liquid water exits the home.

In both scenarios the air and water vapor coming into the home contain the same amount of energy (I think we agree on that). But in Scenario 2, the air and liquid water exiting the home contain less energy than the air and water vapor exiting the home in Scenario 1 (I’m not sure we agree on that… if not, look up “enthalpy of condensation” in wikipedia). Since Scenario 2 has less energy loss from the home, where do you suppose the “saved” energy goes? The first law of thermodynamics says energy must be conserved. The answer is that the energy (the enthalpy of condensation) is released inside the home in the form of heat.

]]> By: JohnC http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-9019 JohnC Mon, 23 Jan 2012 21:32:16 +0000 http://www.iwilltry.org/b/?p=384#comment-9019 Hi Rob, Sounds like a great way to cool a house and keep it dry, but as far as gaining heat from cool moist air that enters the house through cracks and the like, your just bringing in cool moist air then heating it to room temperature removing the moisture and releasing it back out of the building along with the heat gain that was added from the building. Also you will be dumping a percentage of that heat down the drain. Hi Rob, Sounds like a great way to cool a house and keep it dry, but as far as gaining heat from cool moist air that enters the house through cracks and the like, your just bringing in cool moist air then heating it to room temperature removing the moisture and releasing it back out of the building along with the heat gain that was added from the building. Also you will be dumping a percentage of that heat down the drain.

]]> By: Rob http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-8969 Rob Sun, 15 Jan 2012 20:35:42 +0000 http://www.iwilltry.org/b/?p=384#comment-8969 Hi JohnC. I agree that a house can be treated as a closed system. Standard practice in thermodynamic problem solving is to identify the closed system and identify mass and energy transfer mechanisms into and out of the system. It may be true that the transmission line is the only direct energy transfer into the home (excluding solar radiation), but there is mass transfer into and out of the closed system in the form or air infiltration. If that were not the case you would quickly exhaust all the oxygen in your home and suffocate. The amount of air infiltration is much more significant than you might imagine (typical minimum recommendation is 3 to 4 air changes per hour and houses that are sealed well still need to provide that using ventilation fans). If the temperature of the outgoing air is higher than the temperature of the incoming air, then I'm sure you would agree that represents a form of heat loss from the home. Likewise, if you condense water from the incoming air resulting in drier outgoing air plus outgoing liquid water (poured down the drain), then that represents a form of heat gain within the home. The amount of heat gained is simply the heat of vaporization of the water. Hi JohnC. I agree that a house can be treated as a closed system. Standard practice in thermodynamic problem solving is to identify the closed system and identify mass and energy transfer mechanisms into and out of the system. It may be true that the transmission line is the only direct energy transfer into the home (excluding solar radiation), but there is mass transfer into and out of the closed system in the form or air infiltration. If that were not the case you would quickly exhaust all the oxygen in your home and suffocate. The amount of air infiltration is much more significant than you might imagine (typical minimum recommendation is 3 to 4 air changes per hour and houses that are sealed well still need to provide that using ventilation fans). If the temperature of the outgoing air is higher than the temperature of the incoming air, then I’m sure you would agree that represents a form of heat loss from the home. Likewise, if you condense water from the incoming air resulting in drier outgoing air plus outgoing liquid water (poured down the drain), then that represents a form of heat gain within the home. The amount of heat gained is simply the heat of vaporization of the water.

]]> By: JohnC http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-8968 JohnC Sun, 15 Jan 2012 19:27:47 +0000 http://www.iwilltry.org/b/?p=384#comment-8968 you cant gain heat from a closed system and your house is just that. the only heat gain is coming from the transmission line that is outside of the system and it is powering your dehumidifier. the humid air is already inside the house. you cant gain heat from a closed system and your house is just that. the only heat gain is coming from the transmission line that is outside of the system and it is powering your dehumidifier. the humid air is already inside the house.

]]> By: Brian Smithwick http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-8382 Brian Smithwick Sat, 22 Oct 2011 07:15:29 +0000 http://www.iwilltry.org/b/?p=384#comment-8382 Thanks for this info. I also keep most of my house very cool. But with the dehumidifier running I get about a 3 degree rise in my bedroom. And since I work the night shift the hum of the dehumidifier blocks out other noise. So this was definitely a winning solution for me. Thanks for this info. I also keep most of my house very cool. But with the dehumidifier running I get about a 3 degree rise in my bedroom. And since I work the night shift the hum of the dehumidifier blocks out other noise. So this was definitely a winning solution for me.

]]> By: Reza Nezami http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6656 Reza Nezami Thu, 28 Apr 2011 07:27:04 +0000 http://www.iwilltry.org/b/?p=384#comment-6656 Excellet site and wanderful comments from all. We do need this type of info much more. I have been doing these recommendations since first I bought my old house here in Vancouver 3 years ago. It’s a 60 year old cottage style one story house and I basically paid for the land. I first double glazed the old wood windows with 1/16″ clear plastic glass sheets, resurfaced the floor with used but nice wood floor with good underlay and do use a dehumidifier since beginning. I totally disconnected myself from gas company and pay average 50$ a month for my electricity which is used for everything. I have slowly reduced the temperature inside from 20 to 18 and this year to less than 15 degrees all winter. I use only one small electric heater which is one of those with fake fire display and more importantly it is a mobile one. So we, My wife and I, actually move it when it is needed, though most of the time it is located in the living room. To reduce the consumption we do turn it off during sleep and during day when we are at work. So it is basically used a few hours of evening when we are home. That means inside temperature fluctuates between 16 to 12 during night when temperatur falls. But it really doesnt’ bother us and actually feels great to snug in. One trick we use, which we have learned from our cultural background in middle east is to use a large bed spread to put on top of the heater and sit around it by using it to keep our lower body actually it sometimes even hoter than we can handle:) This is a great trick, because the heating area has been step-wised in the sense that where we are sitting it is above 20 degrees, and as you get farther in the living room it gradients out to 15. I like it that you do bring up this very important point in responding to people comments about how much efficiency of various electric appliances is not important, as long as, they are contributing to heating useful space. This is another one of gimmicks of these industries to sell us new appliances in the name of "Star" rated!! In an area like BC we really do not need to go out and replace a perfectly fine apliance in the name energy efficiency. Sure, if you need to buy one, well, better buy an efficient one since it may be put in a "wrong" place. But we should really more emphasize on locating these electric appliances somewhere they can contribute to our heating rather than spend top money for saving a few $ a year on energy on that appliance. When one think of this way, in fact having a regular ( and not a "STAR" rated one) is actually a benefit! why? because they usually are not located all in the same spot in the house and so they contribute to distribution of heat. As a side note, I just received a letter from Fortis BC, the new owner of Terason Gas, that they are basically threatening, politely of couse, to disconnect my gas meter if I don’t activate it again! Of course in the name of safety!! These sleezy business practices really is outrages. What had from very beginning turned me off on gas is the running fees they would charge you for just previlage of having the option of using it! And consider that gas price has been kept depressed in the market as long as I remember, but not for the consumer. So, no, thanks you. I prefer to pay my hard earned money to BC hydro, at least it is not polluting the environment as much. Thanks and keep up the good site. Excellet site and wanderful comments from all. We do need this type of info much more. I have been doing these recommendations since first I bought my old house here in Vancouver 3 years ago. It’s a 60 year old cottage style one story house and I basically paid for the land. I first double glazed the old wood windows with 1/16″ clear plastic glass sheets, resurfaced the floor with used but nice wood floor with good underlay and do use a dehumidifier since beginning. I totally disconnected myself from gas company and pay average 50$ a month for my electricity which is used for everything. I have slowly reduced the temperature inside from 20 to 18 and this year to less than 15 degrees all winter. I use only one small electric heater which is one of those with fake fire display and more importantly it is a mobile one. So we, My wife and I, actually move it when it is needed, though most of the time it is located in the living room. To reduce the consumption we do turn it off during sleep and during day when we are at work. So it is basically used a few hours of evening when we are home. That means inside temperature fluctuates between 16 to 12 during night when temperatur falls. But it really doesnt’ bother us and actually feels great to snug in. One trick we use, which we have learned from our cultural background in middle east is to use a large bed spread to put on top of the heater and sit around it by using it to keep our lower body actually it sometimes even hoter than we can handle:) This is a great trick, because the heating area has been step-wised in the sense that where we are sitting it is above 20 degrees, and as you get farther in the living room it gradients out to 15.
I like it that you do bring up this very important point in responding to people comments about how much efficiency of various electric appliances is not important, as long as, they are contributing to heating useful space. This is another one of gimmicks of these industries to sell us new appliances in the name of “Star” rated!! In an area like BC we really do not need to go out and replace a perfectly fine apliance in the name energy efficiency. Sure, if you need to buy one, well, better buy an efficient one since it may be put in a “wrong” place. But we should really more emphasize on locating these electric appliances somewhere they can contribute to our heating rather than spend top money for saving a few $ a year on energy on that appliance. When one think of this way, in fact having a regular ( and not a “STAR” rated one) is actually a benefit! why? because they usually are not located all in the same spot in the house and so they contribute to distribution of heat.
As a side note, I just received a letter from Fortis BC, the new owner of Terason Gas, that they are basically threatening, politely of couse, to disconnect my gas meter if I don’t activate it again! Of course in the name of safety!! These sleezy business practices really is outrages. What had from very beginning turned me off on gas is the running fees they would charge you for just previlage of having the option of using it! And consider that gas price has been kept depressed in the market as long as I remember, but not for the consumer. So, no, thanks you. I prefer to pay my hard earned money to BC hydro, at least it is not polluting the environment as much.
Thanks and keep up the good site.

]]> By: Rob http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6535 Rob Sat, 19 Feb 2011 06:58:42 +0000 http://www.iwilltry.org/b/?p=384#comment-6535 Hi Rusty, That would work, but depending how humid your house is to start with, you may find the drier dumps moisture into your home faster than the dehumidifier can remove it, and you may get condensation on windows and walls. Another option is to hang your wet clothing on an indoor rack and run the dehumidifier next to it. That's what we do. I can't recall the last time we used our drier. Hi Rusty,
That would work, but depending how humid your house is to start with, you may find the drier dumps moisture into your home faster than the dehumidifier can remove it, and you may get condensation on windows and walls. Another option is to hang your wet clothing on an indoor rack and run the dehumidifier next to it. That’s what we do. I can’t recall the last time we used our drier.

]]> By: John Sainas http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6520 John Sainas Sat, 12 Feb 2011 20:40:56 +0000 http://www.iwilltry.org/b/?p=384#comment-6520 Hi Rob Thanks for the feedback. We purchased a small Enerstar dehumidifier about $120 on sale at Canadian Tire. I believe it is only 60W of power demand and operate it full time in the unimproved basement of our cottage. The basement is now remarkably warmer and enjoyably dryer. It removes about 1.5 liters of water a day. Intuitively I believe the warm dry basement is contributing to a warmer dryer home, reduced mold potential and probably increases the heat pump efficiency not having to heat moisture laden air. I haven't attempted any power comparison with the heat pump, but given the heat pump compressor is 2-3 kW depending on speed, we seem to have achieved significant benefits at a fraction of the heat pump's power consumption. The dehumidifier is noisy due to high airflow noise but in the basement one barely notices it. We're planning a similar basement installation in North Vancouver. We also plan to experiment with an indoor clothes drying rack in the same room as dehumidifier. Rusty who commented above about clothes drying might be interested to know that in Europe one can buy clothes dryers that operate strictly on dehumidification and I believe they exhaust into the building area. Hi Rob
Thanks for the feedback.

We purchased a small Enerstar dehumidifier about $120 on sale at Canadian Tire. I believe it is only 60W of power demand and operate it full time in the unimproved basement of our cottage. The basement is now remarkably warmer and enjoyably dryer. It removes about 1.5 liters of water a day. Intuitively I believe the warm dry basement is contributing to a warmer dryer home, reduced mold potential and probably increases the heat pump efficiency not having to heat moisture laden air.

I haven’t attempted any power comparison with the heat pump, but given the heat pump compressor is 2-3 kW depending on speed, we seem to have achieved significant benefits at a fraction of the heat pump’s power consumption. The dehumidifier is noisy due to high airflow noise but in the basement one barely notices it.

We’re planning a similar basement installation in North Vancouver. We also plan to experiment with an indoor clothes drying rack in the same room as dehumidifier. Rusty who commented above about clothes drying might be interested to know that in Europe one can buy clothes dryers that operate strictly on dehumidification and I believe they exhaust into the building area.

]]> By: Rusty MacCharles http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6475 Rusty MacCharles Wed, 26 Jan 2011 14:39:30 +0000 http://www.iwilltry.org/b/?p=384#comment-6475 Hi Rob: Our laundry machines are located in an alcove just off the side of our open kitchen-dining area & our main source of heat for the entire home is electric baseboard. I've installed a wood burning stove & do try to have it working through most all of the colder seasons to prevent having to use the electric heat. I've even gone as far as disconecting our dryer's electrical supply because it was constantly being used for undersized loads, while my daughters lived at home & installed a clothes line at the back deck for all laundry drying. Since they've moved on, we still now, just use the clothes line to dry laundry but because of our age & the convenience of having a dryer, I'm hooking it back up soon. My thoughts were, to vent the dryer directly into a de-humidifier & release the expelled heat into that arae of the home, while capturing the moisture content, instead of waisting even more energy by venting it directly outside. Is this possible using typical residential use de-humidifiers? Hi Rob:

Our laundry machines are located in an alcove just off the side of our open kitchen-dining area & our main source of heat for the entire home is electric baseboard. I’ve installed a wood burning stove & do try to have it working through most all of the colder seasons to prevent having to use the electric heat.
I’ve even gone as far as disconecting our dryer’s electrical supply because it was constantly being used for undersized loads, while my daughters lived at home & installed a clothes line at the back deck for all laundry drying.
Since they’ve moved on, we still now, just use the clothes line to dry laundry but because of our age & the convenience of having a dryer, I’m hooking it back up soon.
My thoughts were, to vent the dryer directly into a de-humidifier & release the expelled heat into that arae of the home, while capturing the moisture content, instead of waisting even more energy by venting it directly outside. Is this possible using typical residential use de-humidifiers?

]]> By: Alan O http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6438 Alan O Sat, 08 Jan 2011 07:37:01 +0000 http://www.iwilltry.org/b/?p=384#comment-6438 Thanks for clearing that up Rob... Thanks for clearing that up Rob…

]]> By: Rob http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6434 Rob Fri, 07 Jan 2011 19:09:23 +0000 http://www.iwilltry.org/b/?p=384#comment-6434 Hi Alan, I don't know much about desiccant based dehumidifiers, but the law of conservation of energy effectively states that the process by which condensation occurs is irrelevant. If you start with water vapor and end with liquid water, then you will have released a certain amount of energy. If there is no form of energy storage in the system, then that energy will be released in the form of heat. Thus all dehumidifiers will release "bonus heat". However, their coefficient of performance (ie how much heat energy out per unit of electrical energy in) may vary. Without actually testing, I don't know what type would have a higher COP. Hi Alan,
I don’t know much about desiccant based dehumidifiers, but the law of conservation of energy effectively states that the process by which condensation occurs is irrelevant. If you start with water vapor and end with liquid water, then you will have released a certain amount of energy. If there is no form of energy storage in the system, then that energy will be released in the form of heat. Thus all dehumidifiers will release “bonus heat”. However, their coefficient of performance (ie how much heat energy out per unit of electrical energy in) may vary. Without actually testing, I don’t know what type would have a higher COP.

]]> By: Alan O http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6433 Alan O Fri, 07 Jan 2011 16:51:05 +0000 http://www.iwilltry.org/b/?p=384#comment-6433 Excellent analysis and responses - there seems to be very little info out there regarding the impact and economy of using dehumidifiers in the home. This sounds great for dehumidifiers that make use of a refrigerant and condenser. What about the other domestic dehumidifiers that use desiccant and rotor technology ? I am thinking of buying one of these , but this blog post has caused me to pause. From what I understand (very limited) the silica gel in these systems absorb the water molecules in the air which is then sweated off with a heat source and eventually collected. Would I be correct in assuming that this type of technology would be inferior to the condenser type with regards to generating "bonus heat" ? or do the desiccant systems generate bonus heat via some other process ? Thanks Al Excellent analysis and responses – there seems to be very little info out there regarding the impact and economy of using dehumidifiers in the home.

This sounds great for dehumidifiers that make use of a refrigerant and condenser. What about the other domestic dehumidifiers that use desiccant and rotor technology ? I am thinking of buying one of these , but this blog post has caused me to pause.

From what I understand (very limited) the silica gel in these systems absorb the water molecules in the air which is then sweated off with a heat source and eventually collected. Would I be correct in assuming that this type of technology would be inferior to the condenser type with regards to generating “bonus heat” ? or do the desiccant systems generate bonus heat via some other process ?

Thanks

Al

]]> By: Rob http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6270 Rob Tue, 30 Nov 2010 08:42:33 +0000 http://www.iwilltry.org/b/?p=384#comment-6270 Hi John. The answer is it depends on the cottage ;-). You need to know how many watts it takes to raise the cottage temperature by one degree C. My home (2500 square feet, reasonably insulated), for example, takes about 200W per degree C. If your cottage is similar then your heat pump would draw 1/5th of that or 40W per degree C. Perhaps you need to get the temperature from 12 degrees C up to around 17 to reduce mold. That would require a 200W draw from the heat pump. I bet you could achieve a similar effect by running a 500W dehumidifier on a timer so that it only runs 1/4 of the time (125W average). So I think it's likely that the dehumidifier would be cheaper. Again... all guesswork. I'm no expert on dehumidifier brands or efficiencies so I can't help you there. All I did was test the one I bought. Hi John. The answer is it depends on the cottage ;-) . You need to know how many watts it takes to raise the cottage temperature by one degree C. My home (2500 square feet, reasonably insulated), for example, takes about 200W per degree C. If your cottage is similar then your heat pump would draw 1/5th of that or 40W per degree C. Perhaps you need to get the temperature from 12 degrees C up to around 17 to reduce mold. That would require a 200W draw from the heat pump. I bet you could achieve a similar effect by running a 500W dehumidifier on a timer so that it only runs 1/4 of the time (125W average). So I think it’s likely that the dehumidifier would be cheaper. Again… all guesswork.

I’m no expert on dehumidifier brands or efficiencies so I can’t help you there. All I did was test the one I bought.

]]> By: John Sainas http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6234 John Sainas Thu, 18 Nov 2010 07:49:30 +0000 http://www.iwilltry.org/b/?p=384#comment-6234 Hi Rob Like all others that visit, I enjoy your website and ideas. We're up in North Vancouver. My wife also wears multiple sweaters indoors, but would divorse if she had to resort to touques! We have just finished installing a high efficiency water to air heat pump and HRV system at our coastal cottage (heat pump COP 5ish). We also completed a fairly significant insulation, window, and sealing upgrade. When un-occupied we keep the temp low at 12C and noticed some mold on artwork. I found your website researching dehumidifiers and agree with your COP of 1.5 for dehumidifier heating. But it now leads to the next question. Is it more energy efficient to control moisture and mold with heat pump heat at COP of 5 or with the dehumidier at COP of 1.5? or a combination? I can theorize how to evaluate this, but my background in this area is relatively limited and I'm not sure I'd select appropriate operating conditions to compare. I'll probably resort to experimentation with a $200 humidifier. Could I trouble you for your thoughts on this? Also we researched the enerstar dehumidifier listing and found the 25liters /day sizes were all in about the 1.6 liters/kWhr energy efficiency. The larger they got the more efficient they got. Are there other types of dehumidifiers that operate at significantly higher efficiencies we should be considering? Thanks again John Hi Rob
Like all others that visit, I enjoy your website and ideas. We’re up in North Vancouver. My wife also wears multiple sweaters indoors, but would divorse if she had to resort to touques!

We have just finished installing a high efficiency water to air heat pump and HRV system at our coastal cottage (heat pump COP 5ish). We also completed a fairly significant insulation, window, and sealing upgrade.

When un-occupied we keep the temp low at 12C and noticed some mold on artwork. I found your website researching dehumidifiers and agree with your COP of 1.5 for dehumidifier heating. But it now leads to the next question.

Is it more energy efficient to control moisture and mold with heat pump heat at COP of 5 or with the dehumidier at COP of 1.5? or a combination? I can theorize how to evaluate this, but my background in this area is relatively limited and I’m not sure I’d select appropriate operating conditions to compare. I’ll probably resort to experimentation with a $200 humidifier.

Could I trouble you for your thoughts on this?

Also we researched the enerstar dehumidifier listing and found the 25liters /day sizes were all in about the 1.6 liters/kWhr energy efficiency. The larger they got the more efficient they got. Are there other types of dehumidifiers that operate at significantly higher efficiencies we should be considering?

Thanks again

John

]]> By: Danny Yee http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6219 Danny Yee Wed, 10 Nov 2010 00:41:49 +0000 http://www.iwilltry.org/b/?p=384#comment-6219 Ok, I was confused. It's not "condensation that would have happened anyway" that's the problem, it's the extra evaporation from environmental surfaces that happens when the air humidity drops. So if 2 litres of water end up in the dehumidifier, that may drop the water content of the air by 1 litre and the water content of various surfaces by 1 litre (a net 1 litre condensation) rather than dropping the air water content by 2 litres (for 2 litres of condensation). However I'm not convinced that the furniture and walls will hold that much extra water if the air is at RH 70% than at 60% (which is about what I get from taking 2 litres out of a large room or group of smaller rooms). And if you push the RH much below 60% - and certainly below 50% - it starts getting uncomfortably dry. Ok, I was confused. It’s not “condensation that would have happened anyway” that’s the problem, it’s the extra evaporation from environmental surfaces that happens when the air humidity drops.

So if 2 litres of water end up in the dehumidifier, that may drop the water content of the air by 1 litre and the water content of various surfaces by 1 litre (a net 1 litre condensation) rather than dropping the air water content by 2 litres (for 2 litres of condensation).

However I’m not convinced that the furniture and walls will hold that much extra water if the air is at RH 70% than at 60% (which is about what I get from taking 2 litres out of a large room or group of smaller rooms). And if you push the RH much below 60% – and certainly below 50% – it starts getting uncomfortably dry.

]]> By: Danny Yee http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6218 Danny Yee Wed, 10 Nov 2010 00:20:48 +0000 http://www.iwilltry.org/b/?p=384#comment-6218 Mark, is it not possible that the humidity could just stay at (say) 70% if the dehumidifier is not running, without much natural condensation? I would have thought that any water that condenses onto (say) a sofa would just evaporate again - there'd would be some stable "sofa dampness" (at any given air humidity). One problem with using a dehumidifier for heating may be using up the available humidity - or too much of it. A friend in Stockholm says that she really needs a humidifier, as her apartment is uncomfortably dry. Mark, is it not possible that the humidity could just stay at (say) 70% if the dehumidifier is not running, without much natural condensation? I would have thought that any water that condenses onto (say) a sofa would just evaporate again – there’d would be some stable “sofa dampness” (at any given air humidity).

One problem with using a dehumidifier for heating may be using up the available humidity – or too much of it. A friend in Stockholm says that she really needs a humidifier, as her apartment is uncomfortably dry.

]]> By: Rob http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6203 Rob Mon, 01 Nov 2010 07:22:19 +0000 http://www.iwilltry.org/b/?p=384#comment-6203 Hi Mark, I read your arguments with interest. Thanks for posting. While I agree with the principles you describe, I think the magnitude of their effect is relatively low (at least in my case). When not using a dehumidifier, we notice condensation only when we add moisture to the interior air by having showers or cooking or hanging wet laundry, etc. This "natural condensation" is a tiny amount compared to that induced by the dehumidifier. Also, natural condensation may result in water condensing on walls, windows and such during periods of high internal humidity but this water will evaporate into the home again over time. Unless there is a net accumulation of liquid water, the net heat released into the home is 0. Natural condensation does not result in a net accumulation of liquid water (not in our home, anyway). The dehumidifier on the other hand results in a net accumulation of nearly 10 litres of liquid water per day which is removed from the home in liquid form resulting in a positive net heat release into the home. There is a third "flaw" in the above calculation. I ignored the heat removed from the liquid water after condensation. When the condensed water drips into the dehumidifier reservoir it is just above 0 degrees C. If removed from the home before it warms up (using the dehumidifier's drain tube), there is additional heat input into the home. How much? Suppose the condensed water results is 15 degrees C below ambient. The specific heat capacity of water is about 4 kJ/kg/degreeC. Cooling 3.23kg of water by 15 degrees C releases an additional 194 kJ of heat. You can see why I didn't feel obliged to mention this. Compared to the 7290 kJ of heat released from condensing the water, the additional 194 kJ from further cooling the water releases only about 2-3% more heat into the home. I think the effects you described may be about the same magnitude only in the opposite direction so perhaps they roughly cancel. I do agree with you that my "original calculation ignored distribution". Heating spaces that don't need to be heated isn't efficient (especially perimeter spaces). Unfortunately it's exactly these cooler spaces where people may be tempted to use a dehumidifier to prevent condensation. I prefer to think of my dehumidifier as an electric heater and locate it accordingly. Rob Hi Mark,
I read your arguments with interest. Thanks for posting. While I agree with the principles you describe, I think the magnitude of their effect is relatively low (at least in my case).

When not using a dehumidifier, we notice condensation only when we add moisture to the interior air by having showers or cooking or hanging wet laundry, etc. This “natural condensation” is a tiny amount compared to that induced by the dehumidifier. Also, natural condensation may result in water condensing on walls, windows and such during periods of high internal humidity but this water will evaporate into the home again over time. Unless there is a net accumulation of liquid water, the net heat released into the home is 0. Natural condensation does not result in a net accumulation of liquid water (not in our home, anyway). The dehumidifier on the other hand results in a net accumulation of nearly 10 litres of liquid water per day which is removed from the home in liquid form resulting in a positive net heat release into the home.

There is a third “flaw” in the above calculation. I ignored the heat removed from the liquid water after condensation. When the condensed water drips into the dehumidifier reservoir it is just above 0 degrees C. If removed from the home before it warms up (using the dehumidifier’s drain tube), there is additional heat input into the home. How much? Suppose the condensed water results is 15 degrees C below ambient. The specific heat capacity of water is about 4 kJ/kg/degreeC. Cooling 3.23kg of water by 15 degrees C releases an additional 194 kJ of heat. You can see why I didn’t feel obliged to mention this. Compared to the 7290 kJ of heat released from condensing the water, the additional 194 kJ from further cooling the water releases only about 2-3% more heat into the home. I think the effects you described may be about the same magnitude only in the opposite direction so perhaps they roughly cancel.

I do agree with you that my “original calculation ignored distribution”. Heating spaces that don’t need to be heated isn’t efficient (especially perimeter spaces). Unfortunately it’s exactly these cooler spaces where people may be tempted to use a dehumidifier to prevent condensation. I prefer to think of my dehumidifier as an electric heater and locate it accordingly.

Rob

]]> By: Mark L http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6199 Mark L Fri, 29 Oct 2010 19:54:26 +0000 http://www.iwilltry.org/b/?p=384#comment-6199 Steve> Most of the condensation you mention in your first point is perimeter condensation That's true, but now we're talking about the distribution of heat, in which case we need to consider the thermal characteristics of the space being heated. Rob's original calculation ignored distribution and simply counted all the heat of condensation from the dehumidifer and all the electrical energy as "delivered" heating in some sense. This overstates the coefficient of performance, and in many cases the overstatement would be significant. Cheers, Mark L Steve> Most of the condensation you mention in your first point is perimeter condensation

That’s true, but now we’re talking about the distribution of heat, in which case we need to consider the thermal characteristics of the space being heated. Rob’s original calculation ignored distribution and simply counted all the heat of condensation from the dehumidifer and all the electrical energy as “delivered” heating in some sense. This overstates the coefficient of performance, and in many cases the overstatement would be significant.

Cheers,
Mark L

]]> By: Steve http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6192 Steve Tue, 26 Oct 2010 21:13:17 +0000 http://www.iwilltry.org/b/?p=384#comment-6192 Mark L, Most of the condensation you mention in your first point is perimeter condensation anyway. In my experience of cold housing I would expect most condensation to occur on the (relatively) colder windows in comparison to the walls and/or interior furnishings. As the R values of windows are much lower than walls I'd have thought this isn't the best place for it to be released if making use of the heat is a concern. Wouldn't having it released within the dehumidifier allow for better use of the heat output compared to just using it to temporarily speed up the molecules in the glass of my super-low-R-value window panes? Cheers, Steve Mark L,

Most of the condensation you mention in your first point is perimeter condensation anyway. In my experience of cold housing I would expect most condensation to occur on the (relatively) colder windows in comparison to the walls and/or interior furnishings. As the R values of windows are much lower than walls I’d have thought this isn’t the best place for it to be released if making use of the heat is a concern. Wouldn’t having it released within the dehumidifier allow for better use of the heat output compared to just using it to temporarily speed up the molecules in the glass of my super-low-R-value window panes?

Cheers,
Steve

]]> By: JLundell http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/comment-page-1/#comment-6191 JLundell Tue, 26 Oct 2010 19:57:17 +0000 http://www.iwilltry.org/b/?p=384#comment-6191 PJ, some dehumidifiers have freeze protection; they either pause or run a heater when their coils get too cold. Dunno about noise, though; that doesn't seem to be a big priority. Rob, you can add condenser clothes dryers to your list; they're basically dehumidifiers. Bosch is one vendor. Dehumidifier bonus: dry air feels subjectively warmer (when it's cold, that is). PJ, some dehumidifiers have freeze protection; they either pause or run a heater when their coils get too cold. Dunno about noise, though; that doesn’t seem to be a big priority.

Rob, you can add condenser clothes dryers to your list; they’re basically dehumidifiers. Bosch is one vendor.

Dehumidifier bonus: dry air feels subjectively warmer (when it’s cold, that is).

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