Shop Heating

[RJSakowski]

..............................
I was talking with my HVAC guy in Elk Rapids a few weeks back and he strongly recommends heat pump technology (mini-splits). What he told me was using any kind of fuel to heat air or water gives a max of ~97% efficiency, where heat pumps can hit ~300%.
.............................


John

The rest of the story re: heat pumps is their maximum efficiency occurs when the temperature difference between the heat source and the heat sink is near zero. As the temperature difference increases, the efficiency drops rapidly. A heat pump using a geothermal source is the best bet as ground temperature is fairly constant year around. At my location, the temperature is around 54ºF so heating a shop to 65º is still fairly efficient. Properly utilizing ground heat requires some rather sophisticated equipment. One way that it is done is to use a deep well as the source with a closed loop for the refrigerant. There are open loop systems as well but there is a risk of contaminating the ground water. Another way would be to use a large buried tank.

Simple electrical resistance heating is 100% efficient. The problem is that it is relatively expensive and best used in low demand situations like mild climates or low use areas. My attic workshop has both a mini split heat pump and baseboard resistance heating. The workshop is normally isolated from the rest of the house and isn't heated unless in use. The space has the chimney from our wood furnace running through the center and this will keep the space at around 55 - 60º when unoccupied. I use the resistance heating to bump the temperature up to 65 or 70º when I want to work up there. If the outside temperature is above freezing, I will use the heat pump to maintain the working temperature; otherwise. I use the baseboard heating.

 

[jwmelvin]

The real question is 'Why do I care how efficient it is?'. For the same technology, more efficient should mean less cost, but comparing electric heat pumps to combustion heat is apples to oranges, given that it is unlikely your energy sources cost the same.

That’s a useful position but I think it means only that you’d like to compare heating options by BTU/hr/$. That’s not really so hard to do.

 

[RJSakowski]

That’s the beauty of the Carnot cycle. It moves heat, rather than using an energy source to provide heat directly. So it can move more heat energy than it requires in electric energy. Air conditioners and heat pumps can achieve greater than 100% “efficiency” when you define efficiency as the heat added or removed from the room divided by electricity consumed.

A heat pump operating in refrigeration mode is always less than 100% efficient. Operating in heating mode, it is more than 100% efficient although for large temperature differences, the efficiency is not much greater than 100%. Also, the actual efficiency depends upon design and will always be less than the theoretical efficiency.

The real question is 'Why do I care how efficient it is?'. For the same technology, more efficient should mean less cost, but comparing electric heat pumps to combustion heat is apples to oranges, given that it is unlikely your energy sources cost the same.

Well put. The bottom line is what is the cost in $/Btu.

 

[matthewsx]

wow, your dad skipped 2 grades. very impressive. Not many men fly across the country in a small plane. Yes many do, but many don't.
that's a tough task navigating and flying at the same time across the country. Is he still around?

Sadly we lost him in 2018, I do my best to keep his memory alive and live the best life I can with what he taught me.

I do have the two machine tools and workbench in the photo....

John

 

[vtcnc]

Small shop in VT. About 16x24. Installed a 12Kbtu mini-split. Haven't been through a winter yet with it. Ask me in February when it starts to warm up a bit how it works out. For cooling in the summer, it was the best.

 

[rabler]

. The bottom line is what is the cost in $/Btu.

Maybe. I’d compare that to time to recoup the installation cost. (Is $ total cost or just energy cost?). A simple resistive baseboard heater is cheap. Heat pumps are costly and have ongoing maintenance. And unlike a home, heating probably isn’t 24/7

Rather than apples to oranges, maybe we’re comparing technical jargon to marketing jargon

 

[woodchucker]

So got a question, my son went to get paperwork for the permits, and his local town was not helpful... surprise surprise.
He was trying to get an electrical permit for the new sub panel and another for the mini split. They want him to calculate the whole house.

Do you need a permit usually for a mini split?

 

[matthewsx]

So got a question, my son went to get paperwork for the permits, and his local town was not helpful... surprise surprise.
He was trying to get an electrical permit for the new sub panel and another for the mini split. They want him to calculate the whole house.

Do you need a permit usually for a mini split?

We did not, I ran the electrical for ours.

John

 

[rabler]

So got a question, my son went to get paperwork for the permits, and his local town was not helpful... surprise surprise.
He was trying to get an electrical permit for the new sub panel and another for the mini split. They want him to calculate the whole house.

Do you need a permit usually for a mini split?

Personally, I suspect they do some of these things to steer you toward hiring an electrician over DIY. I suspect they get tired of people wanting the permit office to walk them through the whole design.

 

[woodchucker]

Personally, I suspect they do some of these things to steer you toward hiring an electrician over DIY. I suspect they get tired of people wanting the permit office to walk them through the whole design.

he is hiring an electrician to put the sub panel in, the guy is reluctant to pull a permit , and he's a licensed electrician. That panel will be off the cut off switch by the meter. His house has an outdoor cut off switch... I have not seen that before seems weird.