Optimizing heating in a heat-pump + electric resistive system

Question

Outside, I have a LENNOX 13hpx-036-230-17 compressor:

Inside, the air handler is a LENNOX CBX25UH-036-230-1:

The air handler lists 36,000 BTUH cooling capacity, with r410a at 450psi, cust part # 79w36. I have electric backup heating. (I believe two radiant coils because there are two large (30 and 60A) double pole breakers.)

I have a few questions as a homeowner to help protect the equipment, and run it as efficiently as possible:

1. Is there any minimum outdoor temperature for operating this unit as a heat-pump, below which damage is significantly more likely to occur?
2. Is there any minimum outdoor temperature for operating this unit as a heatpump, below which is it less than 100% efficient?

i.e. I know that radiant/resistive heating strips are 100% efficient at creating heat from electricity, and heat-pumps are something like 300-500% efficient because they move more heat from outside than they produce themselves. I know that heat pump efficiency decreases as outdoor temperature drops.

3. Is there some sort of formula or table that shows the relation between temperature and efficiency?

4. Is the Heat-pump's heating capacity the same as the listed cooling capacity? (36kbtuh) What is a good way to measure this if I want to monitor its proper operation over time?

5. When should I expect it to enter defrost mode? (Is it based on a timer, temperature sensor, weight sensor, or something else?)

6. Do you recommend any sort of awning above the outside unit to keep snow and freezing precipitation off of it? Or any shielding from nearby dryer exhausts?

7. Are the indoor fans in systems like these of negligible amperage, and simply thrown on to one of the electric heating element breakers? Or is my fan likely the 30 A breaker and I have a single coil?

I would like to use my system as long as it will last, as efficiently as possible.

FOLLOWUP:

I got the original installer to come on site and help answer these questions. They showed me how to deduce what coil package was installed:

They said that my unit will sense if it is too cold to run, and shut down on its own, but my climate basically never gets that cold. Also, that my unit is always >100% efficient. Even if there's no heat to pump from outside to inside, it will pump its own waste-heat inside.

They said my unit ships with a 90 minute defrost cycle, and they adjust it to 60 or 30 minutes. I have bought and will be installing a 'demand defrost' system from Mike MacFarland/EnergyDocs: This will radically reduce the number of times my system defrosts, extending its life, and reducing wasted energy. The $135 cost should pay back in 2-4 years depending on how cold my winters are.

My installer also indicated it was common practice to put the fan on the smaller of the two breakers, as it is considered negligible power draw.

In my main panel, I have two double pole breakers for the furnace/air handler. 60A for stage 1 resistive heat, 30A for stage 2. Then an additional 30A double pole for the compressor outside.

Answer 1

1. No. You may risk damaging your unit by running it in cooling mode when it is too cold out (although some systems have safeties around this), but heating in low temperatures should not damage the system.
2. No. A correctly functioning heat pump should not ever drop below 100% efficiency.
3. This is dependent upon the specific heat pump model. Often, manufacturers provide charts/graphs describing the efficiency at different temperatures, but I do not see one available for yours. Two data points are specified; at 47f it is rated at a COP of 3.5 (or 350% electrical efficiency), and 17F a COP of 2.42.
4. No, but the heating capacity is often close, in mild weather. Yours is rated at 33,400 BTU/h at 47f and 21,400 BTU/h at 17f. Measuring this requires two temperature sensors (before and after the coil) and an accurate airflow measurement.
5. Your system defrosts on a timer, after 30/60/90 minutes of compressor run time, depending on a jumper setting. (this is less efficient than smarter systems that detect increased air pressure from from frost blocking air movement through the coils).
6. Protecting the unit from falling ice from eaves, and from accumulation of snow, is a good idea. However, make sure to leave ample space so that the airflow isn't restricted.
7. It says on the side that your blower draws up to 2.3 amps.

Answer 2

If the heat pump has an oporational temp limit it will control itself. Be careful with an awning, it could cause discharge air to recirculate. Not good. Keep the filters clean and don't use much night set-back