I can't believe it's really happening!

[emydura]

I'm still experimenting but I built a big pond which sits underneath one of the benches. I heat the water to 26oC or so. This has been pretty effective in increasing the humidity - by 20-30%. Unfortunately the water heater stopped the other day so I'm currently trying to work out what is wrong with it.

David

 

[Ozpaph]

These are the US guys who make foggers/humidifiers - http://www.hydrofogger.com/products_spare_parts

As I understand it, as the temperature drops the humidity drops. Not much you can do about it in winter if you have a non-heated orchid house.
But if its an issue I would use fogger nozzles UNDER the benches to damp the floor. Cycle with a tap timer for a minute or so every hour - cheap, efficient and water-wise!
Heating a water pool/bath will increase the ambient temp just above the water but as the temp drops (moving away from the water) so does the humidity. I use a water bath (+aquarium heater) directly under my flasklings over winter. Keeps them warm but use an ultrasonic fogger to increase the humidity (in an enclosed space).

 

[emydura]

These are the US guys who make foggers/humidifiers - http://www.hydrofogger.com/products_spare_parts

As I understand it, as the temperature drops the humidity drops. Not much you can do about it in winter if you have a non-heated orchid house.
But if its an issue I would use fogger nozzles UNDER the benches to damp the floor. Cycle with a tap timer for a minute or so every hour - cheap, efficient and water-wise!
Heating a water pool/bath will increase the ambient temp just above the water but as the temp drops (moving away from the water) so does the humidity. I use a water bath (+aquarium heater) directly under my flasklings over winter. Keeps them warm but use an ultrasonic fogger to increase the humidity (in an enclosed space).

I already own a fogger from the US. Best thing I ever bought. But there is no way I can use it at night time in the middle winter. My heating bill is already enormous. Conitinually cooling down the greenhouse with a fogger will make it a lot worse. Then there is the issue of rot. In winter my pipes are often totally frozen so there is no way of providing water to the fogger. We all don't have the luxury of growing our orchids in Brisbane. oke: I use the fogger mostly in summer when the temps are hot and the humidity is low.

The pond setup has increased the humidity in my glasshouse by 20-30% to above 50% which is what I was hoping for.

David

 

[NYEric]

Oh! that kind of fogger. Jaybird makes different sizes, so go for it. But I agree, cant see it in the winter for more thatn a few minutes use.

 

[SlipperFan]

This is an interesting conversation! I didn't think about the idea that the fogger would also cool the air in the Winter -- definitely not desirable here!

My greenhouse is all glass and aluminum, but I do get condensation, so maybe another reason a fogger isn't a good idea in the winter.

But if last winter, the first one for the greenhouse, is typical, I had to wet the floor twice a day to keep the humidity at about 60%. I have thought about putting down one of those rubber hoses the leak all over (intentionally), but I hate the idea of tripping over it all the time, plus the algae that will undoubtedly grow around the constant moisture.

Cold weather is almost here, so we'll see how the humidity holds this time around. Maybe I'll just keep doing the wet-the-floor thing in the winter, and get a fogger for the hot summer days.

Thanks, Ozpaph, for the link. That is one of the ones I've been considering.

 

[NYEric]

I have thought about putting down one of those rubber hoses the leak all over (intentionally), but I hate the idea of tripping over it all the time, plus the algae that will undoubtedly grow around the constant moisture.

AKA, sprinkler hose!

 

[SlipperFan]

No -- it's called a soaker hose. It just drips -- doesn't spray.

 

[NYEric]

Oh, OK.

 

[goldenrose]

I've never had a problem with low humidity in my GH in the winter .....
could it be the 2 open barrels of rainwater?
Wasn't it John M that replaced corner bench supports with water barrels & dropped his heating bill by 20%?

 

[Ozpaph]

I already own a fogger from the US. Best thing I ever bought. But there is no way I can use it at night time in the middle winter. My heating bill is already enormous. Conitinually cooling down the greenhouse with a fogger will make it a lot worse. Then there is the issue of rot. In winter my pipes are often totally frozen so there is no way of providing water to the fogger. We all don't have the luxury of growing our orchids in Brisbane. oke: I use the fogger mostly in summer when the temps are hot and the humidity is low.

The pond setup has increased the humidity in my glasshouse by 20-30% to above 50% which is what I was hoping for.

David

David, I think my point was - its hard to increase humidity if the temperature is low. Here's a link showing the relationship between temp and 'humidity'- http://www.bom.gov.au/lam/humiditycalc.shtml.
Its just not possible to have 'high' humidity when the winter night temp is 10-15 Cel. in your glasshouse, worse if lower.
In winter you have to add more heat to increase the humidity. In summer, like you, I add as much water into the air as I can to lower the temp and raise the humidity.

 

[emydura]

David, I think my point was - its hard to increase humidity if the temperature is low. Here's a link showing the relationship between temp and 'humidity'- http://www.bom.gov.au/lam/humiditycalc.shtml.
Its just not possible to have 'high' humidity when the winter night temp is 10-15 Cel. in your glasshouse, worse if lower.
In winter you have to add more heat to increase the humidity. In summer, like you, I add as much water into the air as I can to lower the temp and raise the humidity.

Thanks. You are correct. But my low humidity (30% in winter) is due to the drying effects of heaters rather than cool temperatures. My minimum temperature in winter is around 16oC. It takes a lot of heat to to keep it that way when it is well below freezing outside. Interestingly my minimum temps in summer is also mainly 16oC (unless we get a really balmy night) but the humidity is around 80% because there is generally no heating involved.

David

 

[quietaustralian]

David, I think my point was - its hard to increase humidity if the temperature is low. Here's a link showing the relationship between temp and 'humidity'- http://www.bom.gov.au/lam/humiditycalc.shtml.
Its just not possible to have 'high' humidity when the winter night temp is 10-15 Cel. in your glasshouse, worse if lower.
In winter you have to add more heat to increase the humidity. In summer, like you, I add as much water into the air as I can to lower the temp and raise the humidity.

Temperature is only one part of the equation, air pressure/dew point are others. At the time of writing its 7.6C here and the relative humidity is 83%, 1020hPa and dew point is 4.9C.

As an aside: I had a conversation recently with someone that was considering evaporative cooling or a fogger, the only problem is that at the hottest time of year the humidity is between 85-100%. The cooling effect of evaporative cooling or a fogger in those humidity ranges at 30C would be between about 3C and 0C. He might as well just run a fan.

Mick

 

[cnycharles]

there are 'sprinkler hoses', though I haven't purposely looked for them to see if they are still made; they are a flat hose that has tiny holes poked into them about every so often so that a band of area around the hose gets something stronger than a mist. if they are still available they would broadcast the water around a little more, if that's desirable over a seeping hose

at times of high humidity you can 'force' fogger coolers to cool a little by moving the air around a lot. I don't remember the mechanism described, but have heard that strong air movement helps them, though at 100% there definitely won't be much!

 

[Ray]

I know I'm coming in WAY late on the conversation, but there seem to be some misconception/misinterpretation going on.

Heaters only "dry out" the air if they are literally drawing humidified air out of the greenhouse. What we most commonly see, and misinterpret at "drying" is a reduction in the RH caused by heating. For example, let's say it is 1°C outside and raining heavily. The RH outside is 100% - the air is saturated, but that absolute mass of water is low. Bring that air inside and heat it up, and while the absolute mass of water in the air is the same, the capacity of the air to hold moisture goes way up, making the relative humidity - the percentage of its capacity - lower.

I also think the concern that a fogger will significantly drive up your heating bill is misplaced.

It takes a certain amount of energy to raise the temperature of a mass of water from A to B, and in this case "B" is a level that causes it to go into the air. That energy has to come from somewhere. Have a pond in the greenhouse, and energy is taken from the air, and put into the water. Have a fogger, and the exact same thing happens, although you've increased the surface area sufficiently to make it happen faster. You will see that energy consumption in your fuel or electric bill. Put a heater in that pond, and the energy is still going to be on your bill, isn't it?

However, if you have a nice, tight greenhouse, with very little leakage, the "spike" in energy consumption will only happen in the initial effort to boost the RH. Once it's in the air, all you're doing is maintaining the temperature, not paying to add more moisture to the air. And as was said, as you increase the humidity, the "cooling effect" of a fogger does down, so "refilling" the air from leaks and door opening shouldn't be significant.

So, that simply means that you need to "batten down all the hatches" to keep from losing the precious humidity and warmth, and you'll keep your costs at a minimum.

Nobody said this was a cheap hobby.

 

[Marc]

Wise words Ray people always seem to mix up relative and absolute humidity.

 

[emydura]

I know I'm coming in WAY late on the conversation, but there seem to be some misconception/misinterpretation going on.

Heaters only "dry out" the air if they are literally drawing humidified air out of the greenhouse. What we most commonly see, and misinterpret at "drying" is a reduction in the RH caused by heating. For example, let's say it is 1°C outside and raining heavily. The RH outside is 100% - the air is saturated, but that absolute mass of water is low. Bring that air inside and heat it up, and while the absolute mass of water in the air is the same, the capacity of the air to hold moisture goes way up, making the relative humidity - the percentage of its capacity - lower.

I also think the concern that a fogger will significantly drive up your heating bill is misplaced.

It takes a certain amount of energy to raise the temperature of a mass of water from A to B, and in this case "B" is a level that causes it to go into the air. That energy has to come from somewhere. Have a pond in the greenhouse, and energy is taken from the air, and put into the water. Have a fogger, and the exact same thing happens, although you've increased the surface area sufficiently to make it happen faster. You will see that energy consumption in your fuel or electric bill. Put a heater in that pond, and the energy is still going to be on your bill, isn't it?

However, if you have a nice, tight greenhouse, with very little leakage, the "spike" in energy consumption will only happen in the initial effort to boost the RH. Once it's in the air, all you're doing is maintaining the temperature, not paying to add more moisture to the air. And as was said, as you increase the humidity, the "cooling effect" of a fogger does down, so "refilling" the air from leaks and door opening shouldn't be significant.

So, that simply means that you need to "batten down all the hatches" to keep from losing the precious humidity and warmth, and you'll keep your costs at a minimum.

Nobody said this was a cheap hobby.

Thanks Ray. I understand. I'm currently looking at moving to a twin-walled polycarbonate greenhouse. They seem to have become so cheap recently. Hopefully that should be more leak proof than my old glass greenhouse.

David

 

[Bjorn]

A timely correction from Ray, - one that I fully agree on. I have however a few comments/additions. Having grown orchids in the norwegian climate in an aluminium structure greenhouse with double sheeted polycarbonate for 15 years, I might have made some experiences that can be useful.
first a comment regarding Rays explanation. Youre absolutely right Ray, the heat is consumed to evaporate water and this is basically a one-time expense. In cold weather the water tends to condense on cold surfaces, theoretically releasing the evaporation energy (enthalpy). This is theoretically. So in principle no addition to the heating bill due to high humidity. This is not entirely correct though since the coefficient of heat-transfer from air to the cold spot is influenced by that humidty so heat loss is bigger (but not that much bigger) with humid air.
I would not recommend to lower humidity though, unless the plants are resting etc. Increasing humidity is not difficult using a hydrofogger or some similar equipment. It should be attached to a hygrostat, so that its fairly well automised. The problem of condensation, may make it difficult to maintain high humidity though, but this is an effect of heat-loss and not the warming itself.
What you should consider is to try to reduce the heat loss. I have experienced that the aluminum structure itself is the most important source of heat-loss. The structure serves as a quite efficient cooling-rib unless the heat transfer is interrupted. Possibly some greenhouses may be available taking that fact into consideration but I have not seen any here in Norway. Well to put it shortly, I mounted an extra set of double-walled polycarbonate inside the structure when the house was erected. Later I installed heat-pumps (can also be used as airconditioning) and this summer, as a consequence of last years ridiculous heating bills (one-full month salary for the period Nov-April!!!) I ripped off the vents closed the opening with poly, and covered also the outside of the house with another, third layer of double-poly. So now it is no vents to open, and six layers of poly-sheeting. Ventilation is taken care of with fans and additional heat reduction by air-con. The light does get much reduced, but there is still enough during summer for cattleyas and also dendrobiums. During the winter light has to be supplied anyhow du to the very low sun. My house does not get sun at all during Dec-January, so I am totally dependent on HPS lamps. These run during winter time and provides heat as well as light. A costly story and also vunreable to power failures. More a worry in winter than in summer, its not only winters that are cold here
Power failures are rare however and the house takes a day to cool down to dangerous levels even in winter.
Hope this contains useful info, I guess its not necessary to go to such extremes for you, but If I was to prioritise, I would have invesed in a fogger and also tried to do something with the aluminium ribs of the house.

 

[Marc]

An alternative to build a greenhouse made with an aluminium or steel frame would be a "plastic" framework. It's pretty common to see this being used as a conservatory attached to a house. Building one specific as a greenhouse should be a possibility as well. Only issue I can see is the cost of the initial purchase.

 

[Ray]

I agree 100% Bjorn. The more-humid air has more mass, so carries more thermal energy with it - lost both to leaks and to the structure faster than the same temperature drier air would. Leaks are a killer.

 

[Ozpaph]

Temperature is only one part of the equation, air pressure/dew point are others. At the time of writing its 7.6C here and the relative humidity is 83%, 1020hPa and dew point is 4.9C.

As an aside: I had a conversation recently with someone that was considering evaporative cooling or a fogger, the only problem is that at the hottest time of year the humidity is between 85-100%. The cooling effect of evaporative cooling or a fogger in those humidity ranges at 30C would be between about 3C and 0C. He might as well just run a fan.

Mick

We can't change air pressure in our growing areas and relative humidity is relative to temperature. We want absolute humidity ie more water in the air at all temps. There is a graph on the same link that shows that RH is very high at low temps ie. the air is saturated but its not holding much water. Now, I'm not sure what's important to the plants, RH or AH. I suppose it doesn't really matter, we're bound by atmospherics and our ability to afford adequate heating in winter.
Fortunately, outside the tropics, high temps are associated with low/medium RH so we can achieve cooling through fogging. And having a fan running helps too.