Trying to design a super efficiant heater

[DSGarcia]

Before I deleted my post and thinking that all heat pumps were efficient (simply moving heat from one side to the other), I was going to reference a link to an electronic [Peltier] heat pump here: **broken link removed**

I then discovered that they were not at all efficient and are used mainly for convienience rather than efficiency: Thermoelectric cooling - Wikipedia, the free encyclopedia and Thermoelectric effect - Wikipedia, the free encyclopedia

 

[ke5frf]

Before I deleted my post and thinking that all heat pumps were efficient (simply moving heat from one side to the other), I was going to reference a link to an electronic [Peltier] heat pump here: **broken link removed**

I then discovered that they were not at all efficient and are used mainly for convienience rather than efficiency: Thermoelectric cooling - Wikipedia, the free encyclopedia and Thermoelectric effect - Wikipedia, the free encyclopedia

Thermoelectric coolers are extremely efficient for cooling or heating very small volumes where the surface area being heated or cooled is comparable in size to the cooler itself, as long as an effective heat exchange is occuring to carry away the heat or cold from the unused side.

 

[tcmtech]

They are not so efficient as cooling devices bu they however do pump heat and are very efficient as heating devices.

 

[ke5frf]

They are not so efficient as cooling devices bu they however do pump heat and are very efficient as heating devices.

You would be surprised. I maintain temperature controlled equipment that consistantly achieves temperatures lower than -60C for small surface areas. As long as an effective heat exchange system is provided it works well. The efficiency is in the directness. Heavy, two stage compressors with three phase motors are also used on equipment I repair, but conveying the cooling medium, glycol, methanol, etc requires insulated tubing where thermal loss is unavoidable. In the systems I'm familiar with, a small single stage compressor circulating coolant at 5C through sealed heatsink fins will give the peltier the extra momentum to cool it down to as cold as -80C.

 

[tcmtech]

Peltier coolers do have the advantage of not having any theoretical lower limits that phase change mechanical systems do. Plus they are very small in comparison.
However their actual energy efficiency is relatively low when compared on a energy input Vs energy pumped when compared to the mechanical equivalent.

An efficient mechanical heat pump can easily pump 3+ times it input energy from cold side to hot side. A peltier tops out at about 40% of its input energy at best.

As I stated earlier they do make very efficient heaters being they use the electrical energy to make heat plus they have the added heat that they pumped over from their cold side. In that sense you get roughly 140% more heat energy from the hot side than what electrical energy was put into them. That extra 40% came form what was taken from the cold side of the device.

 

[crutschow]

Some ice chest style coolers for camping trips have peltiers in them that run off your car battery to keep them cold inside.

Maybe you could use the ice chest for your incubator, since it's already insulated. If you operate the Peltier with reverse current it should heat the chest rather than cool it.

 

[Mr RB]

I'm not quite getting why the heater needs to be "super efficient". With a reasonably well insulated cabinet it should only cost maybe $1 a week to run. How many dollars (and hours) would you spend on peltiers and extra construction, risking unreliability etc to get the $1 a week down to $0.7 a week or something?

 

[KMoffett]

Maybe you could use the ice chest for your incubator, since it's already insulated. If you operate the Peltier with reverse current it should heat the chest rather than cool it.

Many of those "ice chests" already have the option to heat as well as cool. Mine does.

Ken

 

[cbiblis]

I'm not quite getting why the heater needs to be "super efficient". With a reasonably well insulated cabinet it should only cost maybe $1 a week to run. How many dollars (and hours) would you spend on peltiers and extra construction, risking unreliability etc to get the $1 a week down to $0.7 a week or something?

I built high dollar cabinet incubators for 600-800 dollars. One of the most common questions about my incubators are "What makes your incubator different when compared to the sportsmans or the dickeys incubators other than you use walnut instead of painted 1/2" plywood" So of coarse i tell them about the increased r value between the materials, And my custom built thermos using 100ma and my 75ma turner gearmotor with motor control, and that the fan that i use is a .18A not a 1.5a exhaust fan. Also i use 3 leds for lighting (100ma) without the heater, that's 5.5 watts when everything is on. The heater uses 225watts when running. I already saved alot of wattage so far why not finish what i started and upgrade the heater. If i can state that my incubators will never use more than a 100watt light bulb then it would be a sales advantage.

 

[cbiblis]

Pack of 5 91.2W Thermoelectric Cooler Peltier TEC 12V | Virtual Village - US
Here is a place that i can get5 for 6 bucks each and rated at 91.2w at 12v. I could probably find heat sinks to slap on it for cheap from some discount computer surplus.
I would probably need help with a controller so i could set it to run continuous. This would actually make the electronic thermostat obsolete. I could use it as a backup in case there was a malfunction with the peltier.

 

[KMoffett]

Install any heater that uses less than 132.95W.

The real question is: what is the lowest wattage heater that will reach and maintain the desired, uniform, internal temperature in the cabinet.

I think you also may want to think in terms of kilowatt-hours used over time instead of instantaneous watts. I could install a 500W heater that might briefly use 500W, but would back off to a very few watts with a PWM or Phase temp controller, as soon as the cabinet reaches temp. This would also quickly reestablish temp after you open and close the cabinet door.


Ken

 

[cbiblis]

that would work great but where to begin on the circuit? It would have to handle 5 amps, have a temp sensor reading every 250 milliseconds, it would have to step down many times probably every 2 degrees. to keep from over shooting the set temp. So a digital controlled pwm? Do they make such a thing not driven via a computer? Granted this would be cool. But would it be more practical then a peltier with a Potentiometer?

 

[KMoffett]

500w was an extreme example. And yes, they do make PID solid state controllers that will deal with things like overshoot.

You are not going to be able to control a Peltier with just a pot. These are low voltage, high current DC devices that will require an adjustable DC supply, either "linear" (very inefficient...like a pot) or "switching" (more complex). Without temp feedback all your adjustments have to be by lots of tweaking...not a good selling point.

Ken

 

[cbiblis]

So what do you suggest? Other then live it the way it is. So you don't like the peltier idea? Spell out the design your proposing. Thanks for your input. Have a good turkey-day.

 

[Pommie]

I am not going to mention reverse cycle air con or heat pumps. Please do not consider them. If you do then you will be ridiculed.

Mike.

 

[tcmtech]

If you do then you will be ridiculed.

Mike.

You mean selling Eco tards with money grossly overpriced boxes so they save a few dollars in electricity over its working life time isn't worth a bit of ridicule now?

Or should we be giving him jealous praise for finding them and being able to get money out of them so easily, with a bit of smoke and mirror advertising, in the first place?

I find that taking advantage of people too stupid to use common sense reasoning and do basic math is wrong, unless I am apart of it of course!

I have mixed feelings about this project now.

 

[KMoffett]

So what do you suggest? Other then live it the way it is. So you don't like the peltier idea? Spell out the design your proposing. Thanks for your input. Have a good turkey-day.

Today I'm making spaghetti and meatballs for my wife, son, and daughter-in-law. Saturday will be our "turkey day", for all of the family.
So, I'm going to have to put off my involvement for a few hours.

Ken

 

[cbiblis]

You mean selling Eco tards with money grossly overpriced boxes so they save a few dollars in electricity over its working life time isn't worth a bit of ridicule now?

Or should we be giving him jealous praise for finding them and being able to get money out of them so easily, with a bit of smoke and mirror advertising, in the first place?

I find that taking advantage of people too stupid to use common sense reasoning and do basic math is wrong, unless I am apart of it of course!

I have mixed feelings about this project now.

You know you don't have to be an ass. If you don't like the conversation then don't involve yourself in it. I'm just trying to build a better product. I'm not trying to screw anyone over. If it's not worth the effort to use alternative heat types then i can always build a dual element thermostat to run a 180ohm nichrome wire and a 60ohm nichrome wire.(Thanks,Kmoffett for the idea) One would maintain heat the other will compensate for the loss do to opening the door being open. None the less, i ask the questions i do because i don't know enough about it to do it on my own. If you want to help tell me why do don't like an idea, if you have a better idea say it. but don't waste your time and others to ridicule someone for thinking outside of the box. Whether it be right or wrong in your perception.

 

[Sceadwian]

The thing about a heat pump is that it has to pump the heat from somewhere, if the unit is inside a building all you're actually doing is saving a little bit of energy by using a bulky expensive heat pump to steal heat from the room, which comes from the buildings heating system instead of from the electrical outlet... Absolutely zero net gain,so you're not building a better product. Heat pumps can only increase overall system efficiency if the proper temperature gradients are naturally occurring AND outside of the system that it's energy usage is part of.

You gotta think the whole thing through.

 

[cbiblis]

i see what your saying. So if some one had this unit in there house, for say. They would see that the unit is as efficient as claimed to be. However, if they where to check both the unit consumption vs. the house consumption it would more than likely balance out. So, thanks for the interpretation of the previous encrypted spouting out.