Hvac peoples

I think this touches on one of the issues (and maybe misunderstandings) of current heatpumps. Many people have gotten used to programmable setback 'stats, and then relying on Morning Warm-up to get the space up to temp during Occupied Modes (I'm using Commercial buildings terms here, but the idea is the same).

I do this at home as well.

Much like the cooler Discharge Air temps that condensing furnaces put out versus what we all grew-up with, the newer air source HPs don't supply that nice, warm (110* or so ) air that everyone seems to want still. Efficiency just means the Manufacturer is grabbing every last bit of BTU/H out of their equipment as possible, which, in many cases, means lower Discharge Air temps.

We service a couple recently renovated "green" buildings here in Minne-a-no-place with rooftop HPs, and there was a nasty learning curve with the tenants/owners at first, as everyone is used to using standard Night Setback & Morning Warm-up roputines in the BMS system. And why not? It saves money, right?

But as you pointed out, and as I mentioned, HPs don't generate that nice 110* air, so the MWU schedules didn't work, and because the end users were cold every morning, they cranked-up up the stats (more is better, right?) in an effort to get the units running hotter, faster. Guess what happens when stats are turned-up too high, and people forget about them?

Anywhoooo....With the building owner's permission our Service Techs removed the Night Setback and MWU schedules from the BMS schedules over the summer, and they're letting the buildings settle out at a constant, 24/7 temp, as the Consulting Engineers feel that not only will this ease complaints, but also will ultimately save some $$$. So far we've had about 10-12 nights where's it's gotten down to 20* or so, and as far as I've heard (knock on wood), no complaints or Service Calls!

We'll see.

What's funny is that I'm pretty sure our office situation would actually work better if we left our doors open to the shop (which is heated to 60F with a huge gas furnace and blower) and let the HP just run all night. I'm pretty sure the lockout under 10F is because the unit is cold, no air ciruclation on the flat roof and it's been in shade for 18 hrs when it tries to kick on in the morning. The boss insists on turning off the split each night which I can't imagine helps it run when the temps plummet, but since it takes all of about 4 minutes to heat our tiny spaces it probably does save some electricity most nights. When it gets below 10F, we just anticipate it and open our doors to the heated shop to take the chill off, then by 11am the pump typically kicks on and it's back to normal.

The tech behind heat pumps is awesome, but to get the most out of them they need to be used in a certain way and the building should be designed to match. Just like our cars, poor combos perform poorly.