We currently don't have a problem, but I want to learn more about heat transfer between floors to possibly head one off later this winter.

Background:
2 story house with a small to mid sized open foyer, 2 geothermal units (one for each floor) and share 1 closed horizontal loop, daytime thermostat settings of 65 second floor (unoccupied during the day) and 68 first floor, both floors 65 degrees at night.

General Questions:

Since heat rises, is it possible that the first floor system at some point (when it is very cold outside) will not be able to keep up with demand since it wasn't designed to heat both floors?

If so, would making the temperature the same on both floors help?

Any other suggestions?

Thanks!

I have two floors with a separate system for each floor.  I have a geothermal system the heats the first floor and the heat pump from hell for the second story.  I try to minimize the temperature on the second floor when it gets very cold outside, since the genius that installed it didn't bother is install aux heater in it.  Anyway, generally the rooms at the top of the stairs are roughly 3 degrees colder than the first floor, however the master bedroom isn't anywhere near the stairs and it about at 10 degrees cooler then the second floor. It probably would get even colder, but I don't turn down the thermostat down more than 10 degrees lower than the downstairs.  So in general, heat transfer between floors without a clear pathway for the heat is very poor.


       

Don't make me come over there and install auxilliary heat so MRS. Grommit can stay warm.... :)
You neglected to mention that you save money by burning a candle in the winter to heat the master...lol
Joe

TG might benefit from some attic insulation or other work to keep 2nd floor heat from being lost.

I can experiment all I want so long as Mrs. Engineer never experiences a room below 70

My stop gap policy has been to use resistance electric heaters in master bedroom/bath when it's below 30 degrees outside.  Since the thermostat is in the master bedroom the system is off for the second floor during these times, I rely on heat from the first floor to keep the bathroom at the top of the stairs above freezing.  Although I could get an aux heater added to the heat pump, there's no way to get to the coils since it was mounted down with a wooden base.  I suspect that the coils are dirty and it's only a matter of time before complete system failure in the future.  The replacement system will address all of the current system shortfalls. It will probably end up being another heat pump since I'm still paying off the downstairs geo system.   

Does everyone agree that this is not an issue? Our first floor unit is running 3 times as much as the second floor unit (blower time monitored by the thermostats).

Where is the thermostat for the second floor unit?  If it's anywhere, where the flow of warm air from the 1st floor is going to get it it, it's going to throw off it's readings and isn't going to turn on as often as it should.  I would say at the top of the stairs would be a poor chioce for a 2nd floor thermostat location.

 

The thermostat upstairs is at the end of a SMALL central hall (the original location from when the house was built). I agree that it's a poor location and that's why we purchased Honeywell's wireless remote sensor and keep it in an upstairs bedroom. Upstairs is comfortable, but my concern is the first floor unit heating the first AND second floor to a degree (pun intended).

Just wondering if there is anything I can do (with thermostat settings) to minimize this when it gets extremely cold outside. Would identical thermostat settings on both floors help? Guess I could close some doors and vents near the foyer if I have to (to keep more heat downstairs). Guess I was hoping for someone here to come forward with a fantastic idea for us.

Geome,

I am not an HVAC expert. I have a theory. As the weather gets colder, the ratio of heat loss from upstairs to upstairs’ heat gain from downstairs will increase. This alone will require the GSHP for upstairs to run longer.

This theory is based on the assumption that insulation inside walls are the same for both floors, but because of the ceiling, an increase in ∆T between inside and outside temps, results in a greater than proportional heat loss from upstairs vs. downstairs.

Theory aside, slow-turning ceiling fans may help.

Regards,
Masoud

Thanks everyone. I also received a very informative response from engineer (Thank you!). Here it is in the hope it will help others too.

"The open foyer thermally connects both zones. Top zone will rob heat from bottom zone, and this is unavoidable unless top zone thermostat is set several degrees warmer than bottom zone.

No harm is done if one zone (bottom in winter, top in summer) runs way more often than the other as long as you are comfortable. Longer run times are good for efficiency

Set thermostats where you want for comfort. Deviate from those only if one zone falls behind and needs help from the other.

A ceiling fan in the foyer running at low speed might help to isolate the two zones."

I missed this comment before. The "Attic" is has enough headroom, so it's finished space above the 2nd floor. So basically I have a 3rd floor, so I'm very limited in what I can do to insulate above the 2nd floor.  Only half of the 3rd floor is finished heated space, but the plywood floor on the unfinished side limits what I can do there.

 

You could sprayfoam the roof sheathing.

For my part I can only suggest that one shouldn't be compared to the other.
Operating frequency or length of cycle are affected by many things, all come back to size of heating unit vs load.
IOW an oversized unit downstairs may run way less than a right sized unit upstairs.
Or
A right sized unit downstairs may run way less than an undersized unit upstairs.
Or
Free communication between zones will affect performance of each unit.
One tool that is not in my work truck is a stop watch. Many folks use time to suggest trouble (including my father in law), but length of cycle is impacted by many things and most do not indicate trouble.
J

No trouble now. However as it gets colder outside, and IF the run time percentage continues to increase for the downstairs unit compared to the upstairs unit I wanted to ask if there might be a future problem since the downstairs unit is not sized to heat the whole house. I like the idea of adjusting the thermostats per engineers suggestion if this becomes a problem.

We have 2 stage equipment. So far, the systems are still only running in first stage. I assume that if the downstairs system starts running in second stage maybe 70% (?) of the time, that it may be time to adjust the thermostats differently. What do you think? Just trying to get a handle on this (if possible).

I wouldn't worry about it unless you become uncomfortable or if aux begins to operate more often than designed.

Why not deal with things as they come. To much time in the what-if or stop watch diagnostics will make you crazy. Unless you're already a tad OCD. lol
j

I like to think of it as being proactive. Lots of people here have monitoring systems so they can respond very quickly if the notice something that isn't yet a noticable problem and either make adjustments or call for repair. This is the same, but done manually. Guess I could monitor aux as engineer suggested if no one else has an opinion on second stage run time being a possible indicator. I'd rather catch this before aux goes on due to the situation I described. Joe?

Isn't it a requirement for homeowners to have OCD prior to installing geothermal?  Maybe it comes afterwards... 

LOL. You might try letting the circulation fan run continuous as well. It would even out the heat to some extent. If it were me I would disable the aux on the lower floor unit and let it run flat out if it must to maintain the temps on the main floor, but I doubt it would on all but the coldest times. The advantage is since the upper floor isn't running as much the field should be fine, just more runtime on the lower unit.

Brock, 447 posts only qualifies a person as a basic member? What's up with that?

We have aux locked out to just above our balance point per Joe's recommendation. Not sure if the circulation fan will help or hurt since the first floor return is at the other end of the foyer on a wall near the floor - worth considering though. I think the combined loop will be fine too (a possible advantage to having 1 combined loop instead of 2 separate loops and pumps).

Theoretically, how are geothermal units and compressors rated in terms of longevity? I know on average they last for 25 years, but will its life be shorter if it runs more often compared to less often?

Longevity is less a matter of run time and more a matter of number of starts - short cycling is hard on compressors. Think of light bulbs - when do they blow out - nearly always upon being energized.

One parameter to experiment with in order to reduce short cycling and number of starts is the CPH (cycles per hour) setting in the thermostat, if so equipped. Set it as low as possible consistent with comfort. I had mine at 4, now I'm experimenting with 2, but my house has high thermal inertia. Too low CPH may allow house to become uncomfortable between cycles.

I believe 500 posts results in automatic promotion to OCD member, or something like that.