Trying to design a super efficiant heater

[cbiblis]

I am tring to design a super efficient heater for my incubators. So far the only idea i have found was a resistor heater found in telescopes. Here is what i have so far.
I want to run the heater on 120v ac. So if i'm doing this wrong please let me know, or if you know of a more efficient way to heat the incubator please let me know. The incubator is basically 8 cu/ft area heated.

I propose to use 10@ 18ohm 10w ceramic resistors.
(I want to use 10w cause there cheap and easy to get.)
18 x 10 = 180 ohms
115/180 = 0.64 amps
0.64a x 115v = 73.6 watts
73.6/10 =7.36 amp each resistor which is less than 75% of the max

I was also wondering about a spray head spraying the heater to raise the humidity in the incubator.

 

[KMoffett]

Resistive heaters are all 100% efficient. All power is converted to heat. (until they glow...then some is converter to light ) The iInsulating material on the heater affects heat transfer rate, but it's still all heat. The fastest transfer rate is with open nichrome wire elements. In making you incubator more efficient there are two factors: insulation and circulation. Insulation reduces heat loss, and circulation puts the heat where you need it.

Ken

 

[cbiblis]

nichrome wire is hard to come by with the specs i need to make it work. Also the idea behind the resistors is to use the insulation to store the heat to reduce cycle times. Do you agree with my assessment?

 

[Externet]

Ken said it right.
You cannot make a more efficient heater; you can make a more efficient chamber.

Disemboweling toasters and many heaters yield nichrome wire. Light bulbs on a dimmer is to consider.

Any mass added in the heat chamber will reduce cycling; be a piece of lead, a potato, or a cup of water.

Miguel

 

[cbiblis]

Here is the thing, correct me if i'm wrong but a ceramic heater it more efficient then a strait nichrome wire due to the storage of heat. I have compared the KWH on a nichrome heater and the KWH on a ceramic heater and the difference was 40% more efficient. This is why i am considering the ceramic resistors instead of the nichrome.

 

[MikeMl]

Here is the thing, correct me if i'm wrong but a ceramic heater it more efficient then a strait nichrome wire due to the storage of heat. I have compared the KWH on a nichrome heater and the KWH on a ceramic heater and the difference was 40% more efficient. This is why i am considering the ceramic resistors instead of the nichrome.

A Watt is a Watt is a Watt... it matters not Watt the heater is made of

 

[KMoffett]

Here is the thing, correct me if i'm wrong but a ceramic heater it more efficient then a strait nichrome wire due to the storage of heat. I have compared the KWH on a nichrome heater and the KWH on a ceramic heater and the difference was 40% more efficient. This is why i am considering the ceramic resistors instead of the nichrome.

Can you post links to where you saw these spec's?

Ken

 

[dougy83]

Resistive heaters are all 100% efficient.

So what's the heating efficiency of a heat pump then?

 

[Nigel Goodwin]

So what's the heating efficiency of a heat pump then?

The better the pump, the lower it will be - the idea is to pump, not to generate heat.

 

[Boncuk]

Also the idea behind the resistors is to use the insulation to store the heat to reduce cycle times. Do you agree with my assessment?

The idea of an incubator is achieving a very accurate temperature of 37.5deg/C.

Using heaters storing heat (like high power ceramic insulator type resistors) you'll get a temperature overshoot every time heating is disabled (accumulative heating). Depending on the incubator size the temperature increase might get as high as 2deg/C over the desired temperature reducing hatch rate.

Using a microcontroller and software enabling the MCU to look ahaed (tendency) activation of heaters can be interrupted by a using a certain lead time. This lead time will only be valid for a certain temperature difference (between amibient air and incubator air). A better solution is using proportional heater control and probably a long period (1 to 2.5 minutes) integral part.

I have designed an incubator control circuit controlling heat, humidification and egg turner. After some experiments I kicked out the integral part since proportional control suffices with an accuracy of ±0.2deg/C.

Using a triac or SSR to switch on and off the heater shouldn't be a problem. There won't be burnt contacts (like using a relay) and switching is done silently no matter how many cycles you apply.

For comparison look at high quality soldering stations. They cycle like hell and do it for 10 to 15 years without having to replace any part.

Boncuk

 

[indulis]

You might want to consider a PID controller for the heater(s).

 

[Hayato]

Here is the thing, correct me if i'm wrong but a ceramic heater it more efficient then a strait nichrome wire due to the storage of heat. I have compared the KWH on a nichrome heater and the KWH on a ceramic heater and the difference was 40% more efficient. This is why i am considering the ceramic resistors instead of the nichrome.

I think that you are confusing the things up.

Efficiency is what do you need to spend to get what you want.

Every heater has an efficiency of 100% or near it, because the whole energy is being converted to heat.
Remember: P = U²/i

Now, with a ceramic casing you are going to have more inertia. It will take long to heat and it will take long to cool. But the ammount of heat energy transfered to the incubator is the same.

 

[crutschow]

So what's the heating efficiency of a heat pump then?

If you look at heat out versus energy in, then a heat pump is always more than 100% efficient.

 

[DSGarcia]

Deleted by poster (I misspoke).

 

[cbiblis]

Ok then, i will consider what has been said thanks for the input.

 

[cbiblis]

Ok guys I'll give in to the nichrome 60 wire. I found a place that sells by the foot. I ordered it today. Here is the question now. The incubator needs to run at 99.5 degrees. Most of the incubators out there are running 60 ohms taking 225 watts to run. Can i gain efficiency with more resistance? I will play around with length when i get it but i was wondering if there was a formula floating around that would tell me were to start. I wonder if with the proper setting the wire could be set to heat to 99.5 degrees and stay constant at that temp. Then the only thing the thermostat would have to do is to keep it from exceeding the set temp. What do you think about that? My idea is that there wouldn't be start up spikes that gobble up power.

 

[MikeMl]

You can only gain "efficiency" by reducing the heat lost from the box, i.e. improve the "R Value" of the insulation. In the limit, if you could insulate the incubator with 24"-thick styro-foam or urethane insulation, you could heat it with a Watt or two. A 2 Watt light bulb in a 20 quart styro-foam beer cooler will keep the inside of the beer cooler at ~75degF even though the ambient temperature is well below freezing.

 

[cbiblis]

I like the beer reference. Now your talking my language. LOL

 

[cbiblis]

I think that the problem is the two vent holes in the box that keep the oxygen level high and co2 levels down. I was thinking of a circuit using a o2 sensor that would turn on a air pump to inject fresh air through the heat element. What do you think about that one?

 

[Boncuk]

Measuring CO2 will be some kind of extravagant.

All you need is a set of holes behind the fan (which is required for equal air distribution anyway) and put a sliding door over the holes to regulate fresh air.

Drill some vent holes near the bottom of the incubator box to force excessive air (overpressure in the box) out where it is supposed bo be cooler than the heated air in the upper region.

About like this:

Boncuk