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Post by numerouno on Sept 13, 2013 14:53:37 GMT
Any heat gain in your system originates from the utility, that is the losses.
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Post by icefisher on Sept 13, 2013 17:28:50 GMT
I am siding with Andrew on this one. Here is why.
A dehumidifier is a small refrigerator with a catch basin. The power coming in operates this refrigerator. The output, hot coil side versus cold side is a wash, no net heat gain.
Inefficiencies in the system is basically friction which is expressed as heat. Thus also is a wash.
By the law of energy conservation the whole operation of the machine is a wash.
But, we have moist air at X temperature. That means the air has a much higher enthalpy than dry air. When the operation is done (without considering latent heat) the enthalpy of the dry air is the same but the enthalpy of the water in the basin is less than the water vapor it came from.
So latent heat has been released and it is used to warm everything, the air, the dehumidifier, and the water in the basin.
Now I am disagreeing with Magellan. He has a point though. Warm humid air feels warmer than warm dry air. Thats primarily because it denies you the loss of the heat of evaporation from your skin. But cold dry air will also cause more evaporation from your skin than cold humid air and make you feel colder. Again its the latent heat processes doing this, but you feeling colder means you are heating the air more.
I disagree about the rising dry air. Humid air rises faster as its lighter. But humid air also warms ceilings faster by condensation and thus reduces your skin heat losses from radiation a bit more.
So Magellan has misidentified of the object in question. He is looking at a person and the discussion is the room. When you cool faster you increase the enthalpy of the room faster. That doesn't result in a room temperature change directly but it can.
Any time you can induce a release of latent heat you are going to cause a temperature rise somewhere in the system assuming its not taken up by another latent heat process.
In the systems talked about at length you cannot cause a rise above the melting point for the release of latent heat of fusion. A similar limitation occurs for the release of latent heat of condensation, but its just more complicated of a concept as it does not have an established temperature in that it depends upon the moisture content of the air.
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Post by nonentropic on Sept 13, 2013 18:38:50 GMT
this is silly.
discussions of efficiency etc have no meaning.
the energy expressed as temperature in the room where a dehumidifier runs is increased by the utility purchased watts and the condensation energy released in the phase change of water from a gas to liquid.
the discussion about how this feels to occupants of the room is about preferences etc. and there will be differences here.
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Post by Andrew on Sept 14, 2013 3:26:10 GMT
Any heat gain in your system originates from the utility, that is the losses. At the moment this remains your poorly constructed theory where: --------------------------------- 1. you claim the heat pump has to work harder to cool humid air because it contains latent heat, where somehow less water vapour gets condensed because of something that you have not yet identified as being a higher cold side temperature than without that latent heat, because of the presence of water vapour. Once you agree the cold side of the dehumidifier is warmer with humid air than with dry air, your explanations will be more easily read. You already agree that latent heat of fusion causes icey water to be warmer than if no latent heat was available. 2. You have not expressed clearly what happens to this latent heat once it is extracted by a cooling system that later uses the energy extracted to reheat the air it had cooled earlier. You appear to agree the latent heat is extracted and yet fail to produce a coherent explanation where it goes. 3. You have many times talked about free energy where clearly some source of heat is required to evaporate the water to create humid air. Talking about free energy is rather tedious. Clearly if a heat source is required to evaporate water to create humid air and then later we use an engine to extract the heat that was earlier used in the warming of water we cannot legitimately talk about 'free energy'. Clearly we are talking about a zero sum use of energy. A ground source heat pump for example requires what you are calling 'free energy' and they work well. Without the summer time solar heat source to create the warm ground temperature the pumps would be useless. 4. None of your answers have so far had clear explanations of dehumidifier operation, where the dehumidifier has a cold side and a warm side so that dry air passing in through the cold side and then out through the warm side will be warmer than the air in the room. Instead you have focused on cooling as if the dehumidifier is cooling in isolation to the existance of the hot side that immediately reheats the air. ------------------------ Whatever you are talking about is poorly expressed. If you are saying a heat pump requires more electrical power to operate in continuous mode when the cold side is warmer, and the hot side is only warmer by the amount of extra supply energy, we already know a heat pump works more efficiently for various warm side temperatures if the cold side is warmer. However it seems to be the case that dehumidifier current increases as the cold side temperature increases on the outside of the cooling coil. |
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Post by numerouno on Sept 14, 2013 5:42:26 GMT
You have in effect a heat pump with both the indoor and the outdoor unit within the same room, and what you are seeking to gain is the condensation of the moisture in the room. However, the continuous operation and cooling of the system will require energy that is mora than what you are gaining from the condensation. Therefore, what you will have in the way of net heat is the losses of the system that are drawn from the utility. You may want to picture this situation as a "real" heat pump that has the outdoor and the indoor unit. I'm not expecting much of a gain in energy from moist air at the outdoor unit. If you have calculations or studies that show that a dehumidifier can be used as a practical heat source, you may want to show them. |
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Post by Andrew on Sept 14, 2013 6:12:53 GMT
You have in effect a heat pump with both the indoor and the outdoor unit within the same room, and what you are seeking to gain is the condensation of the moisture in the room. However, the continuous operation and cooling of the system will require energy that is mora than what you are gaining from the condensation. Therefore, what you will have in the way of net heat is the losses of the system that are drawn from the utility. You may want to picture this situation as a "real" heat pump that has the outdoor and the indoor unit. I'm not expecting much of a gain in energy from moist air at the outdoor unit. If you have calculations or studies that show that a dehumidifier can be used as a practical heat source, you may want to show them. >>You have in effect a heat pump with both the indoor and the outdoor unit within the same room, and what you are seeking to gain is the condensation of the moisture in the room. We dont seek to gain 'the consensation of the moisture in the room.' We seek to extract the latent heat of condensation which no longer exists in the room after extraction. Where does it go?  We extracted it from the humid air. Where did it go?? >>However, the continuous operation and cooling of the system will require energy that is mora than what you are gaining from the condensation. Probably correct, and particularly so if the air is around 21C and only ordinary amounts of water are condensed. >>Therefore, what you will have in the way of net heat is the losses of the system that are drawn from the utility. There is no therefore about it at all. There are the large input energies of dehumidifier operation and then there is the small amount of extracted latent heat of condensation! Where does it go? The total heat is what you call the losses drawn from the utility plus the extracted latent heat of condensation. --------------- What actually precisely do you mean by the losses drawn by the utility? ? >>Any heat gain in your system originates from the utility, that is the losses. 1. Clearly the dehumidifier power consumption heats the room 2. You are talking about something that you are calling losses drawn by the utility which you appear to be saying is something to do with net heat production I have no idea what you are talking about. We know that heat pump power heats the room. What is this thing you are calling net heating??? Where does that originate from if it does not originate from heat pump power? If heat pump power heats the room and latent heat of condensation has been extracted from the room where has the latent heat of condensation gone? ? |
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Post by magellan on Oct 20, 2013 2:55:25 GMT
Andrew, We have a geothermal heating/cooling system and also a dehumidifier now (Frigidaire FAD504DWD) because since sealing up the crawl space there is no air ventilation in the winter (use a homemade Wave Ventilation in summer) and the RH was getting excessively high in the house. The Water Furnace could not keep up with the amount of humidity in the house. Even at 70 degF, it seemed warm. Wondering why, I went into the crawl space and discovered the contractor that did some remodeling had completely cobbled the clothes drier vent allowing it to leak directly into the crawl space. Not only that, but the vent connection in the back of the drier worked loose, soaking the floor with water eventually making its way to the crawl space floor. A huge area is now water soaked. What appeared to be a washing machine leak was actually the drier humidifying the utility room, but we didn't notice it because the doors are shut when the clothes are being washed/dried. I was p'd off to say the least. If you want a job done right, do it yourself. What they did under the house was cut off the fresh air hose and used that for the clothes drier and connected to the fresh air vent! The furnace fresh air hose was just hanging there and the second vent had no hose at all and blocked. So instead of drawing fresh air outside air (required by code) it was taking it from the crawl space, and because the furnace has an outlet at each end of the crawl space (mainly to heat floors in winter), it is positive pressurizing it, effectively recirculating the air from the crawl space, through the fresh air intake hanging there, into the [Merv 13] filters and exiting out of the floor vents. No wonder the filters were getting dirty so fast. Bad. Bad. Bad. Not only is it bad, but a fire hazard because the hose is just insulated plastic slinky hose. I digress. The dehumidifier is situated in the living room and runs 24/7, dumped twice a day, just to keep the house at <50% RH. The back part of the house is about 3-4 degF colder. The crawl space is 65-70% although was close to 80% prior to using the dehumidifier so things are drying out. When the outside temp is in the high 30's (F) or above, the furnace actually doesn't turn on much of the night. I can't find my Kill-o-Watt meter so don't know what the draw is, but have read some people reporting $50-60/mo to operate 24/7 (don't recall cost/kWh). In any event, the dehumidifier is in essence a heat pump, but in order to get much savings (COP) from it, outside air needs to be used. Currently because of the humidity problem in the crawl space, there is no shortage of humidity to continually replenish the dehumidifier. If you're into doing DIY heat pump projects, here's the place to go: ecorenovator.org/forum/geothermal-heat-pumps/ |
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Post by Andrew on Oct 20, 2013 4:11:09 GMT
Andrew, the dehumidifier is in essence a heat pump, but in order to get much savings (COP) from it, outside air needs to be used. Currently because of the humidity problem in the crawl space, there is no shortage of humidity to continually replenish the dehumidifier. If you're into doing DIY heat pump projects, here's the place to go: ecorenovator.org/forum/geothermal-heat-pumps/Sorry to hear about your renovation hassles. I am not sure what you are saying. I was never suggesting a dehumidifier will heat a room in a cost effective manner, I was just saying that it will produce more warming energy than the power it consumes. Are you agreeing with that? |
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Post by sigurdur on Oct 20, 2013 4:18:54 GMT
good link Magellan.
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Post by magellan on Oct 21, 2013 3:47:51 GMT
Andrew, the dehumidifier is in essence a heat pump, but in order to get much savings (COP) from it, outside air needs to be used. Currently because of the humidity problem in the crawl space, there is no shortage of humidity to continually replenish the dehumidifier. If you're into doing DIY heat pump projects, here's the place to go: ecorenovator.org/forum/geothermal-heat-pumps/Sorry to hear about your renovation hassles. I am not sure what you are saying. I was never suggesting a dehumidifier will heat a room in a cost effective manner, I was just saying that it will produce more warming energy than the power it consumes. Are you agreeing with that? Yes, maybe COP of 1.25 or so, possibly more; it's debatable. To get more COP, they need to use outside air. Read some of the posts. It is interesting though that at 45-50 degF, the furnace never turns on while the dehumidifier is running. In fact, it's 49 outside now and the A/C is about to turn on. Here is the basic layout of our home. It's a typical 3 bedroom ranch style, well insulated. I think the DH is rated at around 500 watts, maybe a bit less. I doubt a 500 watt resistive element heater could heat the area as efficiently with the humidity exceeding 65 RH as it was. Right now there's no shortage of water in the air, and after running constant for the past week it stays between 45-50 RH. It is much more comfortable than it was. If I placed the DH right under the furnace intake (thermostat is directly across from it), the A/C would turn on all time screwing up the temps everywhere in the house.  There are commercial units used in large auto plant warehouses (and other such places) that operate at COP ~3 or greater. Metal doesn't rust below RH of 50, so they need to dehumidify. The neat thing is these $200 units can be made to exceed even 3 under the right conditions. Their weak link is the compressor. I've tried the very projects on that website years ago with mixed results. It was a farmer magazine I believe the idea came from, wish I could remember the name. Eventually when I stopped heating with corn and determined to never go back to splitting wood again, I gave up and bought a Water Furnace in 2010. We figure after next year it will have about paid for itself. After fixing the plumbing/vent issues, I'm going to take full advantage of the desuperheater (see page 11 here www.waterfurnace.com/Envision/pdf/IM1585.pdf) of the geothermal system by adding a second water heater in series. In summer we basically get "free" hot water with the A/C running (actually much more waste heat available). In winter using one tank it saves about 30% in heating cost for the water, but with two tanks much more can be saved. If I didn't have a geothermal system, I'd definitely make DHW desuperheater using a cheap dehumidifier similar to how that one guy did in the link. |
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Post by Andrew on Oct 21, 2013 5:03:41 GMT
Sorry to hear about your renovation hassles. I am not sure what you are saying. I was never suggesting a dehumidifier will heat a room in a cost effective manner, I was just saying that it will produce more warming energy than the power it consumes. Are you agreeing with that? Yes, maybe COP of 1.25 or so, possibly more; it's debatable. To get more COP, they need to use outside air. Read some of the posts. It is interesting though that at 45-50 degF, the furnace never turns on while the dehumidifier is running. In fact, it's 49 outside now and the A/C is about to turn on. Here is the basic layout of our home. It's a typical 3 bedroom ranch style, well insulated. I think the DH is rated at around 500 watts, maybe a bit less. I doubt a 500 watt resistive element heater could heat the area as efficiently with the humidity exceeding 65 RH as it was. Right now there's no shortage of water in the air, and after running constant for the past week it stays between 45-50 RH. It is much more comfortable than it was. If I placed the DH right under the furnace intake (thermostat is directly across from it), the A/C would turn on all time screwing up the temps everywhere in the house. There are commercial units used in large auto plant warehouses (and other such places) that operate at COP ~3 or greater. Metal doesn't rust below RH of 50, so they need to dehumidify. The neat thing is these $200 units can be made to exceed even 3 under the right conditions. Their weak link is the compressor. I've tried the very projects on that website years ago with mixed results. It was a farmer magazine I believe the idea came from, wish I could remember the name. Eventually when I stopped heating with corn and determined to never go back to splitting wood again, I gave up and bought a Water Furnace in 2010. We figure after next year it will have about paid for itself. After fixing the plumbing/vent issues, I'm going to take full advantage of the desuperheater (see page 11 here www.waterfurnace.com/Envision/pdf/IM1585.pdf) of the geothermal system by adding a second water heater in series. In summer we basically get "free" hot water with the A/C running (actually much more waste heat available). In winter using one tank it saves about 30% in heating cost for the water, but with two tanks much more can be saved. If I didn't have a geothermal system, I'd definitely make DHW desuperheater using a cheap dehumidifier similar to how that one guy did in the link. I have read a reputable Finnish heat pump manufacturers literature that desuperheaters provide free heat if they are otherwise unconnected and so can be used for example for free underfloor heating of an outside path. What seems to be the case is that an 'unloaded' heat pump system that is just circulating refridgerant without warming or cooling the two heat exchanges uses less power than a 'loaded' unit, so that the more you maximise the heat extraction ability of the exchangers the more work the pump motor has to do. Edit: You dont seem to making a claim of free heat though, but rather just using the heat taken from the warm air to heat hot water |
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