Cheap warehouse dehumidifiers?

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#486850 28-Jun-2011 13:15

jaymz: What are your plans for it? Drying out the whole house, or only certain rooms? We use ours to dry clothes (seperate room)

I think you'd be better off using a dryer, I'm sure that's more efficient.

Although this would suggest not.

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timmmay

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#486853 28-Jun-2011 13:20

bazzer:
jaymz: What are your plans for it? Drying out the whole house, or only certain rooms? We use ours to dry clothes (seperate room)

I think you'd be better off using a dryer, I'm sure that's more efficient.

I thought about that earlier, I wonder if it's true. A drier blows warm dry air through the clothes, then if it's set up correctly that warm damp air gets sent outside, throwing away the heat you paid for. With a dehumidifier the heat stays in the room and the water gets put into a container. It's possible that a dehumidifier could be more efficient.

A heat pump clothes drier with a heat recovery unit/heat exchanger built into the output to prewarm incoming air could be very very efficient.

jaymz

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#486855 28-Jun-2011 13:23

bazzer:
jaymz: What are your plans for it? Drying out the whole house, or only certain rooms? We use ours to dry clothes (seperate room)

I think you'd be better off using a dryer, I'm sure that's more efficient.

Possibly, but a clothes dryer only performs one funtion. whereas a dehumidifier performs several more.

To be honest, the cost of running a dehumidifier is really low (from our experience)
We run a "cent-a-meter" which shows us our power usage in real time, and the difference between when it is running and not is around 1-2cents an hour (calibrated to 26cents per unit of power)

Plus, when you add on the cost of buying a dryer it would be cheaper to use the dehumidifier.

We manage washing clothes quite well too, clothes sit and dry for a couple of days before needing to be worn (in reality they are dry after one night in with the dehumidifier.

haha, as you can tell, I have already investigated the option of buying a dryer instead :)

Dulouz

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#486860 28-Jun-2011 13:27

I have a old home with heat pump, insulation, extraction fans, vapor barrier but still have condensation issues, will a dehumidifier help?

Amanon

jaymz

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#486862 28-Jun-2011 13:30

A quick look on the consumer.org.nz website reveals the following estimations of running cost:

Dehumidifier @ 200Watts = $1.15 per 24 hours
Dehumidifier @ 400Watts = $2.30 per 24 hours

Clothes Dryer 5kg Load @ 1800Watts = $0.99 per load (not sure of times)
Clothes Dryer 3.5kg Load @ 1800Watts = $0.81 per load (again, not sure of times)

Edit:
They calculated costs using the following information:

"Cost is calculated for typical uses at an average cost of 24c/unit of electricity and hot water at 22c/unit."

bazzer

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#486866 28-Jun-2011 13:32

jaymz:
bazzer:
jaymz: What are your plans for it? Drying out the whole house, or only certain rooms? We use ours to dry clothes (seperate room)

I think you'd be better off using a dryer, I'm sure that's more efficient.

Possibly, but a clothes dryer only performs one funtion. whereas a dehumidifier performs several more.

To be honest, the cost of running a dehumidifier is really low (from our experience)
We run a "cent-a-meter" which shows us our power usage in real time, and the difference between when it is running and not is around 1-2cents an hour (calibrated to 26cents per unit of power)

Plus, when you add on the cost of buying a dryer it would be cheaper to use the dehumidifier.

We manage washing clothes quite well too, clothes sit and dry for a couple of days before needing to be worn (in reality they are dry after one night in with the dehumidifier.

haha, as you can tell, I have already investigated the option of buying a dryer instead :)

We did the same and I resisted for a long time, but in the end a dryer is a lot more convenient. As I edited above, I don't even know if it actually is more efficient!

Your cost analysis is interesting, because I think dehumidifiers get a bad rep for using a lot of power. Still, 1-2c would indicate power usage of only 70W which seems unlikely?

timmmay

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#486871 28-Jun-2011 13:36

Dulouz: I have a old home with heat pump, insulation, extraction fans, vapor barrier but still have condensation issues, will a dehumidifier help?

The problem is there's warm, moist air inside, even people breathing put out quite a lot of moisture and some heat. When the warm moist air hits the cold window the water condenses. The two ways to prevent that are to remove the moisture (difficult), or remove the cold surface.

Double glazing is one solution, retrofit is much cheaper than redoing your windows. Another option is a heat recovery ventilation system, which will keep clean, fresh air in your house, while not throwing away the air you've warmed. I don't like the big vendors with lots of marketing, from memory Cleanaire in Chch does a good system. Still there's still moisture in the air, get rid of it all and it gets hard to breathe. Dehumifiers in each bedroom might work, but it's loud and expensive.

I have exactly the same setup, old house fully insulated with a heat pump. It's not practical to run dehumidifiers, plus they're loud. The solution that worked best for me was retrofit double glazing. It cost me about $4000 to have three bedrooms, a lounge, and a front door double glazed. Overnight I changed from puddles on my windowsills that were a good half cm deep to having a light mist on the windows. The moisture's still in the rooms, it just doesn't condense. I have a simple ventilation system that I turn on during the day that dries the house out while i'm at work, making use of the slightly warmer air in the ceiling cavity.

I use Magnetite for my retrofit double glazing and had no end of trouble with the Wellington franchise. The company and system itself is great, but this guy was a dishonest con artist, but he's gone now, so i'll recommend them again. Just make sure you pay a small deposit with the balance on completion.

If I were starting from scratch i'd have double glazed windows, a heat recovery ventilation system, and a heat pump. I'd make sure the HRV system and the heat pump were integrated, working together to put warm air into each room, but usable independently as well.

jaymz

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#486877 28-Jun-2011 13:44

bazzer:
We did the same and I resisted for a long time, but in the end a dryer is a lot more convenient. As I edited above, I don't even know if it actually is more efficient!

Your cost analysis is interesting, because I think dehumidifiers get a bad rep for using a lot of power. Still, 1-2c would indicate power usage of only 70W which seems unlikely?

Apologies, I didn't see your edit.

I worked out when i first brought our dehumidifier that if warm dry air comes out, i can use it to dry all manner of things :)

I wonder if i have my power usage wrong, as you said 70Watts does sound not right. I will check tonight and confirm back here. The unit will use more power at start up and during defrost cycles, so I wonder if I caught it during lower power usage stages.

bazzer

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#486878 28-Jun-2011 13:47

jaymz:
bazzer:
We did the same and I resisted for a long time, but in the end a dryer is a lot more convenient. As I edited above, I don't even know if it actually is more efficient!

Your cost analysis is interesting, because I think dehumidifiers get a bad rep for using a lot of power. Still, 1-2c would indicate power usage of only 70W which seems unlikely?

Apologies, I didn't see your edit.

I worked out when i first brought our dehumidifier that if warm dry air comes out, i can use it to dry all manner of things :)

I wonder if i have my power usage wrong, as you said 70Watts does sound not right. I will check tonight and confirm back here. The unit will use more power at start up and during defrost cycles, so I wonder if I caught it during lower power usage stages.

Not your fault, it was a late edit!

jaymz

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#486881 28-Jun-2011 13:51

timmmay:
Dulouz: I have a old home with heat pump, insulation, extraction fans, vapor barrier but still have condensation issues, will a dehumidifier help?

I have a simple ventilation system that I turn on during the day that dries the house out while i'm at work, making use of the slightly warmer air in the ceiling cavity.

If I were starting from scratch i'd have double glazed windows, a heat recovery ventilation system, and a heat pump. I'd make sure the HRV system and the heat pump were integrated, working together to put warm air into each room, but usable independently as well.

Question, do you have a tin or tiled roof?

The reason I ask is we have a concrete tile roof and the sun during the day (winter time) doesn't warm the roof space up (warmer in the house and outside).

For us, that would mean pushing cold air into the house during the day. For us, leaving a couple of windows open provides more than enough air flow to help keep the house dry.

timmmay

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#486884 28-Jun-2011 14:02

jaymz:
Question, do you have a tin or tiled roof?

The reason I ask is we have a concrete tile roof and the sun during the day (winter time) doesn't warm the roof space up (warmer in the house and outside).

For us, that would mean pushing cold air into the house during the day. For us, leaving a couple of windows open provides more than enough air flow to help keep the house dry.

I have a tin roof. I had a temperature monitoring system up there for a few months, once the sun's been out for a couple of hours it's anywhere between 1 and 6 degrees warmer in the roof cavity than in the house. Once the sun goes down it falls to the same temperature as outside, so I turn it off from sundown to sun up.

Heat Recovery Ventilation systems can stay on at night, because instead of just running a fan that pushes air out the cracks in your house it sucks clean air in from outside, heats it from the stale moist air it takes from the house, and so you get fresh, pre-warmed air. It's not perfect, there's some waste, but it's better than the alternative.

One issue i've been thinking off is insulation. Insulation cover must be solid without gaps, otherwise it loses a lot of effectiveness. For example, according to consumer tests, putting four standard downlights in to a room means you need to double your heating, using say a 6KW heat pump instead of 3KW (you can't insulate over downlights, and most let a draft into the house). When you cut holes in your ceiling to install ducts you're doing the same sort of thing. In my case the duct runs under the insulation for a while, but it's still a significant gap in the insulation. I'm having my downlights removed this week, the ceiling sealed, insulation put over the top, and ceiling dome lights put in. I hope it reduces the heating bill a little, but mostly i'm doing it for efficiency.

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#486897 28-Jun-2011 14:26

We have a cheap Harvey Norman one at home, it is rubbish at night when it is cold (in winter) but it is better than nothing. I find it takes about 4 litres out over 12 hours when our back room hasn't been done in a while. It is useless at drying clothes and the air coming out is barely warmed.

If we could afford a better one we would get one. Interesting comparison to a clothes dryer, we can't have one as our house is too small but it may be a point I can use next time I speak to the Mrs about it.

Wonder if I could borrow a freinds to prove it's worth ???

edited for accuracy

Jaxson

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#486938 28-Jun-2011 15:16

I'd be careful that when your dehumidifier is outputting 'warm air' it's not because it's running it's own little electric element heater. That's not coming from any mechanical losses/perceived gains etc, that's just burning your electricity to make heat. As mentioned earlier, running the unit when the room was naturally warmer anyway would be cheaper, if this was possible in your instance.

timmmay

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#486940 28-Jun-2011 15:19

I wonder if the better dehumidifiers do have a small heater to prewarm the incoming air. I believe it's easier to get moisture out of warm air. That's why power consumption isn't entirely bad, in winter, it may help it be more effective at its job.

Skolink

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#486945 28-Jun-2011 15:21

timmmay: Heat Recovery Ventilation systems can stay on at night, because instead of just running a fan that pushes air out the cracks in your house it sucks clean air in from outside, heats it from the stale moist air it takes from the house, and so you get fresh, pre-warmed air. It's not perfect, there's some waste, but it's better than the alternative.

Just to clarify, Heat Recovery Ventillation should not be confused with the 'HRV' system which Marc Ellis markets, they are two different things. The Marc Ellis type system is what timmmay has installed, with no heat exchanger.

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