I need an expert opinion. Currently considering purchasing a basement dehumidifier (100 pint) which uses 6.8 amps at 115 v. This unit costs about $1,900. called a SaniDry.
I already have a room dehumidifier (50 pint) from sears and it uses 7.2 amps at 115v. My question is; would the energy savings be cost effective or would it make more sense to use the current dehumidifier? I'm not familiar with amps and volts in regards to cost etc..
I appreciate any help. I know this is the wrong forum for this question but the crowd here is "A LOT" smarter than many other forums, even the hvac people.

thanks

 

Without considering the purchase price, (capital acquisition cost), you are only concerned with the ratio of watts (of electricity) to pints (of water removed). For each machine divide the watts required by the machine to remove the number of pints of water removed. This will find the number of watts to remove one pint. The machine that requires the lowest number of watts to remove the 1 pint of water is cheapest to operate.

If you do not know the watts required, but the manufacturer gives you the volts and amps to remove a quantity of water, you can multiply volts and amps. The result will be in volt-amps, but will be close enough in watts for all practical calculations.

The new unit:
115 vac x 6.8 amps equals approximately 782 watts, divide that by 100 pints give a power requirement of 7.82 watts per pint.

The Sears unit:
115 vac x 7.2 amps equals approximately 828 watts, divide by 50 pints gives a power requirement of 16.56 watts per pint.

The new unit is slightly more than twice as efficient. Your power company should be able to tell you your cost per Kilowatt (1000 watts). Form there you can calculate your savings per pint

savings per pint == cost per kilowatt/1000 x (16.56 - 7.82)

....and from that your payback period using some assumed timeframe.

Savings per (month?) == Savings per pint x no of pints removed over some elapsted time (month?);

Payback time in (months?) = $1900 / Savings per (month?)


... Your welcome.

 

I can't argue watts and amps, but I have a question that might change the tech answer.

One unit is described as 50 pint, the other is described as 100 pint. Is that how much it removes from the air in an hour or just the capacity of the holding tank for the unit?

If it's how much moisture is removed in an hour, then the calculations would appear to be correct. If it's the capacity of the tank, then there is not enough information given to answer the question since we don't know how much is being processed.

 

Yep. You would need to know how long to fill the tank to the stated capacity.

 

The 100 and 50 pint refers to the amount of moisture removed in a 24 hour period. My utility charges .194838 per kwh for generation and delivery. Basically the larger new unit would remove twice as much moisture and use less energy to do it. Found some more info:
Voltage x Current = Wattage.
Wattage x Time = Energy Use
Watt-hours per Day x (1 Kilowatt/1000 Watts) = Kilowatt-hours per Day

so 115vx7.2amps =828watts (operating for 24 hours = 19872 watts) SEARS
&115vx6.8amps =782watts (operating for 12 hours = 9384. watts) SANIDRY

**assuming the sanidry will work less because the capacity is twice the other units?**

19.872 kwh x (.194838 energy cost) = $3.87 per day or $1412.55 per year SEARS
9.384 kwh x (.194838 energy cost) = $1.82 per day or $664.30 per year SANIDRY

saving $748.25 per year and taking 2.53 year to break even.
Further calculating total cost including installation, pump etc.. $2700.
3.60 years to break even with total cost.

Does that look right?

 

Does the dehumidifier compressor really run 24 hours per day all year long?

This seems like an immense amount of energy and money to have to spend yearly.

Did you consider blocking the source of the humidity entering your basement so the dehumidifier would not be needed or at least run much less?

Seal the floor with a vapor barrier coating. Cover a dirt or gravel crawl space with a heavy gage plastic vapor barrier. Attach a plastic vapor barrier to all walls. If the walls are finished, you can still paint on a vapor barrier coating and repaint. Cover up any open sump pit.

If you have water seepage, it still may pay for the foundation cracks to be sealed or for drain tile to be installed if there currently is none.

 

Don, It is unlikely that the unit would operate all the time, especially in the winter when humidity and condensation would be less. I wanted to compare apples to apples in the scenario above (worst case scenario). As for the repairs you described, I have tried to "find" where the problem is coming from but to date have not been able to. We see no visible water in the entire 1800 sf basement. No wet spots on walls or floor, no pipe leaks, the AC units have a condensate pump which shoots the water outside and no standing water anywhere (basement is unfinished and all is visable.) Even the french drain and sump pit is dry. We don't even have a pump in it. The only conclusion I have come up with is condensation, the average temp down there is always around 60-65f. We are starting to notice the damp musty odor and some visible green/gray mold on our stored items.
Thanks to all for the help.

 

The dry sump pit is a big concern. seal the top of the pit completely with plastic and a strong adhesive tape to make it air tight.

There is typically 4" diameter perforated plastic drain pipe placed around the footing of the foundation and it drains into the sump pit. The drains in your window wells also connect to this drain pipe. There is often a slight vacuum in the basement due to normal venting in the house and this will cause air to be sucked into the window well drains underground and through the drain pipe into the sump pit. Needless to say, this air seeping into the sump pit will be much more humid than the air outside due to it's long underground path through damp soil. Also this is also the prime way Radon seeps into homes.

Water vapor slowly penetrates the concrete or cinder block walls of your basement even if they appear to be dry. Due to the large surface area of the walls and floor it doesn't take much to create the damp air. a vapor barrier would go a long way toward reducing the moisture.

 

I have done several tests around the walls and floors by taping aluminum foil with good adhesive tape to see if any humidity appears on top of the foil or underneath the foil therefore giving a clue as to seepage or condensation. I have gotten negative results for both, although I have not tested the entire wall and floor. As for the sump pit, you may be on to something. I will try it out. It currently has a cover made of thick ABS, but it is not air tight. I will seal that up and see. As an update; I have set up my dehumidifiers I had and connected one to the condensate pump to drain outside. They have been running for a day and a half continuous. I am hoping that it is doing this just because it is the initial dry out period until everything dries out. Otherwise I may have to spring for the 100 pint unit.
Thanks for the tips.

 

115vx6.8amps =782watts. = 0.782 kilowatts. Depending on the "power factor" of the motor, the electric meter may charge you for more than that. The power factor just measures a kind of inefficiency that happens in magnetic (inductive) loads. Most small electric motors have a power factor of about 0.9, so a typical small motor that reads 6.8 amps on your amp meter will actually draw 115 x 6.8 / 0.9 = 868 volt amps, and the power company will charge you for 868 watts even though the hand-held amp meter says it should be only 782.

Ignoring the power factor for now, 0.782 kilowatts x 24 hours/day x 365 days/year = 6867 kilowatt hours per year. At $0.12 per kilowatt hour (your cost may be different, it's on your electric bill), that comes to $824 per year if the unit operates continuously. That is in addition to the capital cost of the unit, and replacing the worn-out unit every couple of years. If you can reduce the humidity by passive means, you can reduce the operating time of the dehumidifier.

I suspect you could significantly reduce the humidity, and the dehumidifier run time, by air-sealing and water-proofing. Find out how the humidity is getting in, and close those paths. Concrete is a likely culprit in a basement -- because it normally permeable. Soil or gravel, if any is exposed, is a sure culprit. Air infiltration is a possibility, too. Any exhaust fans in the bathrooms or kitchen will create a vacuum in the whole house, which pulls in humidity from the soil, and humid outside air. If any of the doors or windows have no or poor weatherstrip, that can let outside air in or out, even without any fans. Depending on the shape of the house, leaky windows on the leeward side can make a vacuum inside the house, too.

Aside from completely rebuilding the house, there are a lot of little things you can do. Most of them cost a lot less than $824, and most of them only need to be done once every ten years or so. And you don't have to do them all at once. You can do one or two each weekend. Waterproof coating on cement (walls and floors). Plastic vapor barrier on soil or gravel. Grade the outside soil so it drains away from the house. Make sure your roof gutters drain far from the house. Both in the basement and above ground, look for holes or cracks and fill them with caulk or foam. (Little holes and cracks are commonly found where plumbing or electrical passes through walls or ceilings. One little hole doesn't pass much air or much humidity. A few hundred of them add up to a lot.) Open drains can be covered. Weather strip all of the doors and windows. To fix the air-pressure problem, you can add a "make up" air intake. (That is just a duct from outside to the return-air box on your air handler. It allows the suction of the air handler to pull some outside air into the house, and pressurizes the whole house so the air-leakage is outbound instead of inbound.)

In the bargain, you will reduce your air conditioning and heating bill. After you have the leaks stopped, add some insulation for even bigger savings.