Heating a tiny shed

[OldMcDonald]

I have a wooden garden shed about 6m x 4m with walls and ceiling reasonably well insulated. I use it for several purposes – seed house, vegetable production, 8 stacking wormeries, wine cellar and some general storage. It is quite full, so little empty air space, or spare floor space.

I presently use a permanently switched on 1.5kW fan heater at floor level on a very low setting and it is sufficient to maintain 14º to 15ºC (just below 60F) most of the time. It operates only infrequently during the day. The temperature does drop on cold nights (only very slight frosts now and again), but a max/min shows it has not gone below 12.3º in over a year at distance from the heater. That is acceptable for everything in there. Daytime requirements will be less than the 1.5kW.

I am in the process of switching electricity tariffs so that I have a reduced rate from 00.30 to 7.30 a.m. My idea is to continue using the fan heater during the lower rate electricity time as well as making use of this time for my LED grow lights. I want the fan in use because it blows warmer air around the wormeries when on and this raises their temperature above the ambient air temperature in the shed and they are doing OK.

I wondered whether it would be feasible to charge a battery for the 7hrs when electric costs are lower, then use that stored power for an oil filled radiator even for part of the remaining time. This is the only question I want to be answered, and I ask it because I have no experience of using battery storage. Just think cents instead of pence, and the prices are 16p and 33p/kWh. I would need to buy an inverter and battery, but have a radiator that I could use.

I have posted the foregoing information on dedicated sites, but nobody has answered the question, they just want to tell me all sorts of things I did not ask and make suggestions for alternative heating methods – all of which I either cannot have or do not want. If it is not feasible then I will just stay with what I use at present and experiment with the radiator on a low setting and time switch for during the day.

Please do not waste your time on giving me other ideas. What I have and do does not warrant capital expenditure. The shed is organised in such a way that fixed storage heaters, fires, stoves, heat pumps etc. cannot be used. It needs to be small and mobile, hence the radiator idea.

 

[34Willys]

I have read where people use the TESLA power wall, grid tied, and charge it over night when the rates are low, then switch over to the battery when rates are high. These are wealthy people, so...
The answer is yes, but you need to do the math. I don't know the formula, but power consumption by the radiator, storage size and type of batteries, inefficiency of inverter and converter to charge....
ROI may take a lifetime.
Batteries and inverters are pricey.
We are currently off grid, so dealing with similar issues constantly.
Sorry not much specifics.
Patrick

 

[ponytug]

We have AC batteries, and for heating I would not recommend it. Resistance heating takes a great deal of power. I would consider whether there is something that is in the shed that could soak up the heat overnight and radiate it during the day. We once did something similar with 55gallon drums in a greenhouse to keep it warm overnight. Could you put five or ten gallons of water on top of the radiator? A couple of cement blocks?

Given the small cost difference in the rate, I rather doubt that there is going to be a solution that pencils out if you need to buy anything, but perhaps a rescued immersion heater and drum from a skip...

All the best,

Peter

 

[LouNY]

Heat mass storage would likely be your best bet.
As an example a group 31 Diehard Marine Platinum battery at well over $200 is rated at 885 CCA, 1000 CA,
with a 200 minute reserve which ends up being a 100Ah battery.
So, it ends up to this;
1200 watts hours,

If you need to convert amp hours to watt hours, you can do this by multiplying the battery's amp hours by the battery's voltage. Using that equation, the number of watts a 12 volt 100Ah battery can provide in an hour, would be calculated like this: 100 amp hours x 12V = 1200 watts hours or 1200 watts for one hour.

So not much when used on a resistance heater.

 

[Rockbadchild]

sorry but I have to... I am too curious of your reasoning... why not just have the oil radiator instead of both system? what disadvantage you see with the oil system because if it's just for the fan you could have just a fan on batteries for the peak hours that take minimum power and there is oil radiator that don't need any power.

 

[HawkinsHollow]

It is worth a shot!
I think if you made sure you used the cheap electricity to get the radiator up to temp I could see the battery lasting a while. Even better, if you could figure out a way to heat it up to MAX temp using the cheap electricity then turn it to low for the rest of the day it could last even longer. There is a way to figure out all of this info. but you might need a meter like a kill-a-watt or equivalent to determine power draw over the day then scale your batteries up accordingly. But honestly, you have to wonder would the investment in batteries, inverters, timers, etc. just make it as cost efficient to pay the man for the pricier electricity. Good luck, let us know how it goes.

 

[MAX-24-Dean]

Daytime requirements will be less than the 1.5kW.

I wondered whether it would be feasible to charge a battery for the 7hrs when electric costs are lower, then use that stored power for an oil filled radiator even for part of the remaining time. This is the only question I want to be answered, and I ask it because I have no experience of using battery storage.

Probably not feasible? Unless you have money to burn.

Battery Amp draw. Copper cable sizes (costs) are determined based on having enough ampacity to serve the load.
1500 watts / 12 volts = 125 Amps
1500 watts / 24 volts = 62.5 Amps
1500 watts / 48 volts = 31.25 Amps

You would need to provide more information to determine actual sytem requirements.
It would be helpful to know the total Kw hour usage just to have a starting point.

If the heater used the 1500 watts at a 25% on time over the 7 hours. It would look like this.
7 hours * 1500 watts * .25 = 2625 watt hours or 2.625Kwh

So lets use 3Kwh (3000Wh) per day to size a battery.
3000Wh * 1/.90 (inverter efficiency losses) * 1/24 Volt battery * 1/.50 (maximum battery discharge)
3000Wh * 1.11111 * .041666667 * 2 = 277 Amp hour Battery Minimum.
At a 50 % on time, 6000Wh the minimum Amp hour capacity would need to be approximately 555 Amp hours.
Hope this gives you an idea as a starting point for cost approximations.

Edit: misread your post about the 7 hours. I was thinking 7 hours of needing to run the heater intermittently. But you can plug in the actual watt hours used and figure out battery sizing.

 

[OldMcDonald]

After 17 years a member of TBN you would think I should have learned to ask here first!!!!

Thanks for the responses so far. I have skimmed through them because it is getting late here and will give it more thinking time later, but I am fairly well committed for the next couple of days.

I will be back though, and thanks again.

 

[Lastkidpicked]

After 17 years a member of TBN you would think I should have learned to ask here first!!!!

I agree that there are many knowledgeable folks here, and very generous with their knowledge.

If it will save you some time, you can use my experience so you don't have to repeat it on your own.

We have a shed that is too far away from shore power to "plug it in" and are always looking for better ways to provide heat. We always come back to the same conclusion. Nothing we try is as cheap or efficient as simply plugging it into house power, and that is exactly what we would do if we could.

If you have a curious mind, and are looking at this as an engineering challenge, then go for it! But if you are simply interested in the cheapest way to heat your shed, you are probably already doing it.

 

[Egon]

Heat sink storage with the fan for circulation. No batteries as their cost would exceed that of the small circulatory fan.

There should be current system set ups that could be looked at.

Electric Thermal Storage

This may give some information of heat storage systems.

 

[copytmpmzl]

I have a wooden garden shed about 6m x 4m with walls and ceiling reasonably well insulated. I use it for several purposes – seed house, vegetable production, 8 stacking wormeries, wine cellar and some general storage. It is quite full, so little empty air space, or spare floor space.

I presently use a permanently switched on 1.5kW fan heater at floor level on a very low setting and it is sufficient to maintain 14º to 15ºC (just below 60F) most of the time. It operates only infrequently during the day. The temperature does drop on cold nights (only very slight frosts now and again), but a max/min shows it has not gone below 12.3º in over a year at distance from the heater. That is acceptable for everything in there. Daytime requirements will be less than the 1.5kW.

I am in the process of switching electricity tariffs so that I have a reduced rate from 00.30 to 7.30 a.m. My idea is to continue using the fan heater during the lower rate electricity time as well as making use of this time for my LED grow lights. I want the fan in use because it blows warmer air around the wormeries when on and this raises their temperature above the ambient air temperature in the shed and they are doing OK.

I wondered whether it would be feasible to charge a battery for the 7hrs when electric costs are lower, then use that stored power for an oil filled radiator even for part of the remaining time. This is the only question I want to be answered, and I ask it because I have no experience of using battery storage. Just think cents instead of pence, and the prices are 16p and 33p/kWh. I would need to buy an inverter and battery, but have a radiator that I could use.

I have posted the foregoing information on dedicated sites, but nobody has answered the question, they just want to tell me all sorts of things I did not ask and make suggestions for alternative heating methods – all of which I either cannot have or do not want epoxy garage floor Atlanta. If it is not feasible then I will just stay with what I use at present and experiment with the radiator on a low setting and time switch for during the day.

Please do not waste your time on giving me other ideas. What I have and do does not warrant capital expenditure. The shed is organised in such a way that fixed storage heaters, fires, stoves, heat pumps etc. cannot be used. It needs to be small and mobile, hence the radiator idea.

I'm planning to convert a 12x16 ft shed into a weekend 'hunter's cabin' for when I spend time on my wooded property. Winters get pretty cold (and summers hot) here in middle Georgia so I need to get an off grid option for heating the shed. The options I'm thinking of include: either propane wall-mounted heater or a small wood burning stove. The propane heater seems easy and propane can also power a small refrigerator if I decide to get one. The wood stove means paying for installation and keeping it stoked but firewood is plentiful. Any one know what labor costs could be to get a small stove installed? Any recommendations on which would be better choice.

 

[LouNY]

Firewood is "inexpensive" it seems but then remembering to get the chimney cleaned and if you use the triple wall pipe through the building and up it adds up the cost quite rapidly.
A infrared propane requires no venting.

 

[Jstpssng]

Propane isn't cheap either and if you are planning on one of those unvented heaters, I would not want it in a well insulated building where I am going to be sleeping. A chimney is going to cost you about as much as the heater and tank, and it doesn't take much effort to run a brush through it every couple of months.

For comparison I just have a small 12x32' building I am living in until I get money to pour a foundation and build... I burn >2 cds per year and heat it with a small oil filled radiator when I'm away. That heater is on a thermostat and costs me about 10-20$ per month through the winter.

 

[dstig1]

This is the only question I want to be answered, and I ask it because I have no experience of using battery storage. Just think cents instead of pence, and the prices are 16p and 33p/kWh. I would need to buy an inverter and battery, but have a radiator that I could use.

I have posted the foregoing information on dedicated sites, but nobody has answered the question, they just want to tell me all sorts of things I did not ask and make suggestions for alternative heating methods

Thank you for the good LOL!

But seriously now - I will have you know that this request violates TBN Statute 126.34.2 "Mandatory thread drift process" and Statute 293.6.2 "Disallowance for Respondents actually reading the OP". Since this appears to be your first offense, the fine will likely be reduced. Please report to TBN court for your hearing next Monday.

 

[OldMcDonald]

Armed with the practical experience and theoretical knowledge of responders from several countries on different forums, I have reached the conclusion that my idea is feasible. Whether it is economic is a question that needs a great deal more thought.

Given all the uses of the shed, the most important is maintaining the temperature of the wormeries and containers for seeds and seedlings, each individual ideal being different.

Thinking about the problem, I suddenly recalled Fourier and his Law regarding heat (or cooling) conduction from the ground to the air above it. Many people will know of Fourier from “the greenhouse effect” which keeps earth at a liveable temperature. From farming around the world for longer than many people live I was well aware of this conduction and have used the principle, but had foolishly forgotten about it. In practical terms I can accept a lower air temperature without affecting the plants.

There is a lot of bulk in the shed – maybe two thousand litres of moist “soil”, with a fair bit of the rest of the interior being timber staging and shelves for the plants; storage boxes full of various materials; tools and equipment; water for the plants and soaking corrugated cardboard – large quantities are used in the wormeries and garden. All in all a lot of material that could lose some temperature without doing any harm.

The decomposition of organic materials added to the wormeries (vegetable waste and cardboard) means the temperature of the contents is higher than the air, and this temperature differential is further increased with warm air blowing onto the wormeries from the fan heater. There is some conduction from them when the heater is not on. I need to do some experimentation to see the effect on the soil temperatures of the wormeries and plant containers. I have 1.5kW and 3kW available on the fan heater and 750W, 1250W and 2kW on the radiator so a few combinations that can be tried on low and standard tariffs. This will take time.

The economics of battery storage will be determined by how much electricity I could save. Heat is needed for about 30 weeks a year, so a saving of even £1 a day on electricity costs is worthwhile, but it might not be possible.