Heating and cooling a 30x60

[flynlow8740]

I am considering building a shop, a 30x60x14 pole building. Since I'm starting from scratch I'd like advice on insulation, heat and AC. I'm in Mississippi, so AC would be used more, but I'd like a heat source to leave on all the time to prevent freezing, during our occasional cold snaps, and to be able to warm it up when I'm out there. AC would be part time, only when I'm there and days when the humidity is enough to wet everything. My electric rate is .08 per kWh. Natural gas isn't available, but propane is. It's currently about $2.40 a gallon. Also, please advise on venting and anything else you think I need to know, this is my first large construction project. Thanks in advance!


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[flynlow8740]

I've been looking at window unit AC. What are the pros and cons? I can get the BTUs I need cheaper than a split system.


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[theoldwizard1]

Perfect for a mini-split heat pump !

With that size shop, you are going to need at least 2 air handlers. t will be hard to get warm/cool air from one corner to the opposite corner. If you are going to have an enclosed area (office, etc) you will need an extra one for there.

The good thing is that these can be "slaved" together (operate on one thermostat) or operate independently all from the same compressor.

Not the cheapest to install, but likely the cheapest to operate !

 

[pseudorealityx]

Window units...

Pros: Cheap, easy to install

Cons: Typically not sealed well, limited capacity, limited distribution, no real filtering capability, no gas heat available, "commodity item"


They do work, and are better than portables.

 

[flynlow8740]

For heat I was looking at "hot dawg" style heaters. I was thinking one big one or two small ones, probably would use ceiling fans. It will be heated full time, but it's not hard to keep from freezing here and that's my main concern. I will warm it up while I'm in there. For AC is a 25,000 BTU split really that much better than a 25,000 BTU window unit? Maybe it's just me, but in my experience, heat pumps **** for heating. My house has one and we use space heaters because the heat pump just runs all the time blowing cold air. Is it my system?


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[CNGsaves]

If you rarely have any freezing cold temps being in Mississippi, then I'd just go with normal forced air system (electric) like you'd have in house as what you really want from system is the "CONDITIONING" part of system to eliminate humidity in the air for your climate. You've got low electric rate so your heating bill won't be significant, whereas you will be spending your monthly money for electric on conditioning and cooling.

Insulation and sealed shop will be key to keeping your electric bill down.

You will want to plan your ductwork and air handler location to maximize best conditions where you'll be working most of the time. Thus, you may have zones like "shop" and "office" depending on how you configure the shop and walls you install. Dampers in the ducts could scale down cooling in the "shop" area, if you were instead working mostly in "office" area, or vice versa.

 

[pseudorealityx]

For heat I was looking at "hot dawg" style heaters. I was thinking one big one or two small ones, probably would use ceiling fans. It will be heated full time, but it's not hard to keep from freezing here and that's my main concern. I will warm it up while I'm in there. For AC is a 25,000 BTU split really that much better than a 25,000 BTU window unit? Maybe it's just me, but in my experience, heat pumps **** for heating. My house has one and we use space heaters because the heat pump just runs all the time blowing cold air. Is it my system?


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If your heat pump blows cold air, then it's not working, and you should have it fixed.

You should understand that heat pumps aren't going to supply 110 degree air like a furnace is, but in Mississippi, you don't want/need that. But a modern heat pump, at ~30 degrees outside, which is your average low in winter in Mississippi, can still give you a 20 degree temperature rise. So the air going into your return duct is 65 degrees, and it will spit out 85 degree air. Now 85 degree air isn't going to 'feel' super hot, but that's ok, and that's why it's running so much. In addition to that, a heat pump should be provided with an electric strip heater as an auxiliary heater. This is used both in the situation when the temperature falls low enough that you cannot get enough heat, and also when the unit is in defrost mode.

Fwiw, even if the heat pump is only helping out "a little", it's still going to be 2-3 times MORE efficient than those space heaters. So ANY heat you get out of the heat pump is worth it.

 

[flynlow8740]

What is the advantage of electric heat over propane? I was thinking I could heat cheaper with it and it would feel warmer faster when I go out there in the morning.


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[pseudorealityx]

If you're talking vs. an electric unit heater, the propane is more efficient, but more expensive, and obviously you need to keep supplying propane.

Your correct in that typically you can get MUCH more heat out of any fossil fuel than a an electrical heater assuming typical house/garage electrical service sizes.

 

[theoldwizard1]

Window units...

Pros: Cheap, easy to install

Cons: Typically not sealed well, limited capacity, limited distribution, no real filtering capability, no gas heat available, "commodity item"

Noisy, limited to location. EXPENSIVE TO OPERATE !

Maybe it's just me, but in my experience, heat pumps **** for heating.

It is you or more specifically the heat pump you have installed in your house.

Modern (past 7 years or so) mini-split heat pumps are very efficient and some still operate at 100% efficiency down to 5F ! Because the heat is generated right at the air handler, you get hot or cold exactly where you want it. This is also a negative for multiple small rooms, like a house. For large, open rooms/buildings you need multiple air handler, at additional costs.


It is a classic, "You can pay a lot up front (mini-split), or you can pay a lot more, month after months, later (window/PTAC) !"

 

[theoldwizard1]

Your correct in that typically you can get MUCH more heat out of any fossil fuel than a an electrical RESISTANCE heater assuming typical house/garage electrical service sizes.

Electrical resistance heaters are 100% efficient. The power you put in, is the heat you get out. A good heat pump will run over 300% in heating mode because it is moving the heat available (even below freezing on some models) from outside to inside.

 

[flynlow8740]

Assume I'm in the shop 3-4 hours 3-4 days per week. Will I really see a difference in comfort and the power bill on cooling with a split vs window units? Let's say 2 18000 btu window units and a couple ceiling fans.


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[pseudorealityx]

See a difference? Yes.

Enough of a difference to pony up thousands of dollars in additional expenses? That's up to you.

 

[flynlow8740]

Ok. Thanks for the replies everyone!!


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[930dreamer]

Are you ok with closed cell foam insulation for the shop? This would seal all the draft area's in the building.

 

[slice]

I have 30x40x14. Near galveston tx. 4 ton two speed compressor. Variable speed blower. 16 seer. I pay .10 kW. No prob cooling in summer. I use heat pump. Top summer bill. 75. Top winter bill 125.

 

[Deltarat]

I live in the Ms Delta and have a 30x50. I have 2 25k widow units -$500 each- and it will keep it in the low 70s when it is in the 100s. It also reduces the humidity and keeps out the SKETTERS, which is a big concern here. I have a NG 75k hanging Mr Heater-$500- and and I work in a T shirt all winter.
I have the bubble foil insulation which is not the best.
I just put a new 5T system in my house and the 3t compressor I removed was fairly new and my heat and air guy is looking for me a good used 3t air handler to put it in the shop. Hopefully it will be more efficient and lower power bills.
My electric bill runs $60 a month average and gas about $50 average on level pay. We have a heater in the den we use a lot that is on the gas meter with the shop and my wife's beauty shop is on the light meter.
Let me know if you have any questions.