Heating a small shed

[Old McDonald]

This seems to be the best part of the forum to pose my problem.

 

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

 

I presently use a permanently switched on fan heater at floor level and 1.5kW on a very low setting is sufficient to maintain 14º to 15ºC. It operates only infrequently during the day. The temperature does drop on cold nights (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.

 

I am in the process of switching electricity tariffs so that I have a reduced rate from 00.30 to 7.30 a.m. I am also contemplating installing solar panels on the house roof next year, although it may not happen – a lot of other expenditure needed on a big old house bought last year. I do not have the land for a windmill. 

 

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. These lights are used in summer too. 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. The ideal wormery temperatures would be 20/25ºC but they are doing OK.

 

I wondered whether it would be feasible and economic to have an oil filled radiator on during the rest of the time, charging a battery when electric costs are lower and using that to power the radiator. The usual several kWh storage batteries coupled to PV panels is not economic without the panels. I have a radiator in the house that I could use, and replace with a new one, so the radiator is not quite free. What I have and do does not warrant much capital expenditure.

 

Comments? Suggestions?

[SteamyTea]

Welcome.

 

Have you considered a night storage heater, some of the more modern ones have fans built in. Saves having a battery if some of the power comes from the PV.

There is also air to air heat pumps. These can be quite cheap to run.

 

Usually worth working out the heat losses of any building, even a shed, then you can size a heating system to be in the most efficient window, most if the time.

 

Really comes down to how much you want to spend.

 

Do you know much about LED grow lamps? Often thought about buying some, but don't know enough about plants and getting the best growth out if them.

 

[ProDave]

Air to air heat pump aka air conditioning unit, you get about 4 times as many kW of heat as it consumes kW of electricity.  You can buy one for under £1000 and they are (just) possible to DIY install.

 

Unless your whole house is using storage heaters, I question of the night rate saving is worth it as the day rate will be higher than normal.

[Radian]

1 hour ago, ProDave said:

Air to air heat pump aka air conditioning unit

 

Absolutely! It's got to be perfect in an application currently served by a fan heater. 4 to 5 times the heat energy for the same electricity or 1/4 to 1/5th the cost to keep the same temperatures. 

[Old McDonald]

On 12/11/2022 at 12:31, SteamyTea said:

Welcome.

 

Have you considered a night storage heater, some of the more modern ones have fans built in. Saves having a battery if some of the power comes from the PV.

There is also air to air heat pumps. These can be quite cheap to run.

 

Usually worth working out the heat losses of any building, even a shed, then you can size a heating system to be in the most efficient window, most if the time.

 

Really comes down to how much you want to spend.

 

Do you know much about LED grow lamps? Often thought about buying some, but don't know enough about plants and getting the best growth out if them.

 

A night storage heater is not on my consideration list - Purchase cost, weight, immobility, installation cost, etc. I do not presently have PV and may never have it. I have had storage heaters earlier in life, never liked them then, and whilst they are improved, they still have operational drawbacks.

 

I have a lot of experience of air conditioning units. Over 18 years in Portugal (until last year) every main room in the residential part of the house had one. They do not last too long if in regular use, and whilst they are very good at cooling, they are not good at heating. They may well be efficient in terms of power used, but their heat output is poor. In any event the shed is not suitable to have one installed, and the delivery and installation are not cheap. I am too old and decrepit to do very much myself. That is why I retired and moved here.

 

It would take a big A/c to keep temps up overnight and I doubt it could be achieved. They are not as good as all the hype about them when it comes to heating – very good at cooling though. They constantly have to go into defrost mode when outside temps are low. I admit it was colder in Portugal overnight in winter than it was here last winter, but temps were still low enough to have caused numerous defrost interruptions to their operation. I think this might be the reason they wear out so quickly.

 

There is some heat loss, since it is a shed that was built to suit the site. Insulation is still fairly good, hence the min temp over the last year. I know there is the odd spot that could do with being improved because the sheets used were not exceptionally good fits, and I will probably use cork and/or sheep’s wool to push a bit into them, but it is not really a priority.

 

There is no point in attempting to make everything 100% efficient for my uses – germinate seeds; produce a few veg during the winter when outside they are likely to be blown out of the ground; keep my worms alive even if not breeding to full capacity, and keep my wine stocks at a good storage temperature. As posted, none of those justify much expenditure.

 

I know a bit about grow lamps, but there is plenty of info on the internet for those who know something about plants and their requirements. If you do not have extensive plant growing knowledge I would suggest learning in a small greenhouse, conservatory or similar before trying to use grow lamps.    

  

20 hours ago, ProDave said:

Air to air heat pump aka air conditioning unit, you get about 4 times as many kW of heat as it consumes kW of electricity.  You can buy one for under £1000 and they are (just) possible to DIY install.

 

Unless your whole house is using storage heaters, I question of the night rate saving is worth it as the day rate will be higher than normal.

As above for A/c. CH for the house is by oil (as everybody else on Orkney unless you have your own big windmill) so no other night storage heaters. As mentioned we do have one plug-in radiator that I am willing to use. The day rate is circa 33p and for 7 hours overnight is 16p.

18 hours ago, Radian said:

 

Absolutely! It's got to be perfect in an application currently served by a fan heater. 4 to 5 times the heat energy for the same electricity or 1/4 to 1/5th the cost to keep the same temperatures. 

As above.

 

................

 

Thank you all for your time, unfortunately you have not addressed the issues I raised. The fan heater will be used for part of the time because, as I posted, it serves a specific purpose; I need some heat during the day, but not a lot, and want to know if my idea of using a cheaper rate overnight to store for use during the day (when power costs twice as much) is feasible. I do not know if it is worth pursuing that idea, so I asked the forum members.

 

[ProDave]

16 minutes ago, Old McDonald said:

Thank you all for your time, unfortunately you have not addressed the issues I raised. The fan heater will be used for part of the time because, as I posted, it serves a specific purpose; I need some heat during the day, but not a lot, and want to know if my idea of using a cheaper rate overnight to store for use during the day (when power costs twice as much) is feasible. I do not know if it is worth pursuing that idea, so I asked the forum members.

You have ruled out storage heaters so I don't know what else you expect to store the cheaper night time rate?  Remember ALL the electricity used in your property gets the cheap rate at night, so the 7 night hours that fan heater is running it will be metered at the cheap rate.

 

Look again at the Air to air heat pumps, especially if you are still going to use the fan heater for some specific need as you won't be expecting the A2A unit to do all the heating.  I think you were unlucky with your previous experience with a system that did not perform well. 

[SteamyTea]

8 minutes ago, ProDave said:

  I think you were unlucky with your previous experience with a system that did not perform well. 

Or Portuguese 'heating engineers' are as shit as ours.

Not sure if an A/C unit, designed primarily for cooling is the right choice for heating.

Would have to see the specifications.

 

@Old McDonald

What is the size of this shed, and roughly how thick is the insulation?

We could do a rough heatloss calculation and then get a better idea of what is needed.

Just to clarify, I really meant to suggest that the night storage heaters were charged with PV most of the time.

There is no fundamental difference between a fan heater, a panel heater, a storage heater a heat pump solution. 1 kWh of delivered heat, at the required temperature, is the same as any other 1 kWh of heat delivered.

Why we use standardised units.

[Radian]

6 minutes ago, SteamyTea said:

Or Portuguese 'heating engineers' are as shit as ours.

Not sure if an A/C unit, designed primarily for cooling is the right choice for heating.

Would have to see the specifications.

There are units on the market that are specifically designed for both. Japan seems to be one of the most prominent adopters, hence why Daikin have such an extensive selection. I can only speak from my own experience with a couple of units that reportedly produce a nominal 4kW of heat output (~14000 BTU/h) for 1kW in. To me it seems like nothing short of magic when it fires up. Admittedly I've only experienced it heating when the outdoor temperature was around 10^oC. 

[SteamyTea]

10 minutes ago, Radian said:

~14000 BTU/h for 1kW in.

1.341 British hp if we must embrace BREXIT.

 

[Old McDonald]

Being a newcomer to the forum, I do not want to be rude, or appear ungrateful, but none of you are answering the question I asked. It is very simple. Is it feasible and economic to charge batteries at a cheap rate (in this case 16p per unit) and discharge them through a heater when the rate is twice as much (in this case 33p per unit). If the answer is no, then it is no. If it is yes, then I would appreciate comments and suggestions on the question asked, e.g. best buy for batteries.

 

I have already posted there are no intentions of spending £1000 or more on capital items. I do not want a night storage heater. I do not want a reverse cycle air conditioning unit. I have already said that fitting either to my shed, even if possible, would not warrant the cost. I also posted that installing PV may not happen, so at this stage it does not come into the question I posed.

 

I have only long ago experience of using night storage heaters, but 18 years recent experience of air to air - up to last year; only Japanese makes but several of them, including Daikin. Mitsubishi was the original choice. Fitted in 2003 and I still had two in bedrooms that were very infrequently used.

 

Regular use caused failure of units after about 10 or 12 years - no record kept, so from memory. They are brilliant at cooling a room quickly and keeping it there, but at outside temperatures near or below zero are fairly well useless for heating. Their COP drops dramatically, and worsens the more it goes down.

 

These units are extremely common in Portugal, with most homes of those who can afford them having several, usually of different sizes to suit the rooms. The companies which supply and fit are numerous, so all have a lot of competition and they would not stay in business long if they did not know what they are doing. As stated, the units are brilliant at cooling – outside temps in the mid to high 30s for long spells in summer. I did not have a bad experience with them, they performed just as well as everybody else’s. Every house has some other source of heating, invariably a wood burning fire, whether open or a stove. Wood is plentiful and often free for the effort of collecting and making into useable sizes if you do not have your own timber. Some electric heating in rooms without a fire is normal, but full scale CH is not.

 

I do understand Watts, hours, BTU, COP and so on. I do not have any experience of using stored battery power. That is why I posted in the first place. I thought somebody on the forum might have that experience.

 

I originally posted that the 1.5kW fan heater is adequate for all year round use, and so there is no need to do any calculations. I expect a lower Wattage setting on a radiator would suffice during the day and would experiment to see what is needed. Temperatures here are generally higher than the Scottish mainland. Inverness, also at sea level and a long way south, has lower mean temps than Kirkwall. Most of Japan has a higher mean and hot summers, so, as in Portugal, a/c units are required for cooling, not heating, that is why they are so popular there too.

[Jilly]

I'm not sure if this really answers your question or not, but I've got a portable battery pack thing, it was about £50. You could charge that on economy 7 tarrif and then use it to power the heater in the daytime? It's a very useful bit of kit and has other uses besides the plug socket: a torch, tyre inflation, jump starter. You'd have to keep an eye on your bills or the smart meter to see if it made much difference.

Edited November 15, 2022 by Jilly

[SteamyTea]

It is possible, but probably not practicable for £1000.

Here is an example.

https://www.amazon.co.uk/EF-Portable-Appliances-Charging-Generator/dp/B09J8C9MVF/ref=sr_1_18_sspa

 

But the huge output, is about 40 minutes of running with that storage.

Now you could cobble together your own system with a leisure batter or two, an cheap inverter and a battery charger.  The efficiency will be pretty poor, but it will work.

[Old McDonald]

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.

[Adsibob]

On 12/11/2022 at 12:21, Old McDonald said:

ideal wormery temperatures would be 20/25ºC but they are doing OK.

But this would not be good for storing wine

[Old McDonald]

18 hours ago, Adsibob said:

But this would not be good for storing wine

Yes, I know. Neither is it good for many of the vegetables. The multi-use of the shed complicates the problem.

 

See the penultimate paragraph of my post a couple of hours before yours. I keep the wine (permanently placed bins) where they receive no direct heat and are situated where the temperature does not exceed 14º at this time of year. Summer could be slightly warmer. My previous property (in Portugal) had a huge partly underground wine making and storage cellar - lagar, barrels and individual bottle "holes" (drainpipes forming a wall) for 600 bottles. One must live with what is available.

[limecc]

I've got the problem of heating an outbuilding I've yet to build for occasional use. I purchased a 8kw (yeah right) diesel heater for £120 and might run it on used cooking oil. Plenty of videos on youtube. Normally fitted to heat boats, this one's a portable suitcase heater. Extremely efficient and economical, minimal outlay.