[Woodworkers] Climate Controlled Shops

Dave Heitstuman DaveH at sphcontrols.com
Thu Jul 12 15:02:55 PDT 2018

Here is my 2 cents for whatever it might be worth.  I'm in the commercial HVAC business from the control or building automation side of things.  We are in the energy saving business :)

First of all with gas heat and DX cooling I would set the thermostat and let it rip.  (we have gas and DX in the house)  We also have cheap power here so some of this may not be practical for you.

There are basically 3 things to consider when trying to save energy and setback the temperatures.
#1 Energy cost
#2 How well your shop (or home) retains heat/cool (minimum and maximum outside air temp plays a huge factor in this)
#3 The equipment recovery time (how long it takes to warm or cool the space from setback)
#3a  How long in between trips to the shop.

Backing up, many moons ago (before I was in this racket) I was told by an HVAC tech that if you set your temperature back too far then the equipment will just run longer and harder to get the temperature back up (were were discussing heat recovery).  His theory was that it was more cost effective to maintain a temperature than it was to heat it back up.  Remember it is not just the room temp it is everything in the room (house or shop).  If you keep it at 50 then not only do you have to heat the air you have to heat the furniture and walls and.....  He had a convincing argument at the time.  Bottom line his argument was to only set back a maximum of 6 degrees (heating).
Fast forward I get in this racket and as I learn I ask questions.  The theory was pretty much debunked by just about anyone I talked to.  A few of the older techs would ponder it and respond with something along the lines that it was an interesting theory.  I can tell you that we have our controls in buildings that cannot recover from a 10 degree setback in the dead of winter due to heat loss.  We also have buildings that cannot cool themselves when the temps get into the 90's.  So this proves that equipment sizing, system design, and insulation all matter.

Most importantly I can tell you from experience what I have learned with my shop.  I primarily heat with wood.  Due to the placement of my shop getting gas to it (at the time) was cost prohibitive so I put in a heat pump with electric emergency heat.  I kept my shop at 55 in the winter and 85 in the summer.  These temps are the industry standard for setback in our area for an unoccupied building.  Let's say I go out to the shop on a 20 degree day and don't want to start a fire so I bump the heat up; usually to 70 degrees.  It is too cold for the HP to run so the strip heat comes on.  I am slightly undersized on my strip so it runs for about an hour to get the temp up the 13 degrees.  It will then cycle on and off every 10 minutes or so for awhile and then the cycles start getting longer, every 15 then every 20 and eventually if I am out there long enough the furnace runs 2 or 3 times an hour for a few minutes.  If I am working on a big project that I need to keep stabile I leave the heat at 68 and the furnace runs maybe a few times an hour for a few minutes.  I started realizing a year or so ago that this seems to support what that guy told me all those years ago.   So I am now leaving it at 62 and tracking the usage on our utility bill.  The impact seems to have been non-existent this past winter.
I recently have been living in the shop while the house has undergone a major renovation (Oh how Joe would have loved this tale).  Because of that and our bizarre spring weather I have also learned that keeping the cooling lower seems to keep the HP from running as much.  Or best case it keeps the temperature more stable since the mass is all one temperature and it does not run at night and wake me up.  This seems to have confirmed what I already had surmised, the cooling will run no matter what, so how long do I really want it to run to cool the mass?  I have dropped it to 78 or 80(?) for this summer to see what happens with our power bill.


From: Woodworkers [mailto:woodworkers-bounces at lists.sawdusters.org] On Behalf Of Chuck Steger via Woodworkers
Sent: Thursday, July 12, 2018 11:05 AM
To: A place where woodworkers talk about woodworking
Cc: Chuck Steger
Subject: [Woodworkers] Climate Controlled Shops

For those of you with climate controlled shops, I'm curious on what you leave the temperature at when you are out of the shop? I leave mine at 80 degrees in the summer and 50 degrees in the winter. I figure those temps won't ruin any finish or glue. If I'm in the middle of a glue-up or finishing, I'll leave the temperature around 70 until complete.

For those of you with HVAC knowledge ....  I always bring the temperature up or down in 3 degree increments. In other words, I'll go out in the morning and bring it from 80 to 77, then when at 77 I'll take it to 74, etc. Same with bringing the temperature up. Not sure why I do this. I guess I'm basing it on when I had a heat pump, you would not want a drastic change or the emergency strips (electric strips) would come on. I do not have a heat pump (gas furnace and regular AC) so is this faulty logic? Should I just go straight to 70 in either direction? Any advantage to a slow clime or descent?

Cave Springs, AR

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