Ladia,
Please share these changes and tweaks with the group, maybe we could all learn from your findings.
What was your average monthly heating bill before the changes were made? After?
First I measured temperature exiting from all ports of the heat accumulator in both heating and cooling mode. There was significant temperature difference between top and bottom discharge pipe in cooling mode. The cooling loop was originally connected to the same pipe as heating headers getting higher than desired temperature. After relocating the Toff to the bottom port (return to the HP) performance of the AC improved significantly.
The original control system provided only temperature control in 5 zones while the HP operation was controlled by temperature in the accumulator. Therefore the HP was needlesly running for about an hour or more/day even when there was not demand for heating or cooling.
Switching between heating, cooling or standby had to be done manually. It didn't provide temperature control of hot water that often overheated and popped overheat protection in water heater. When the weather got cooler and AC stopped operating there wasn't hot water until the protection was reset.
Therefore I bought small PLC (LG because it comes with programming software), 24V transformer, 10 relays, two dual temperature controllers, 1 60A contactor, terminal blocks etc and small cabinet. All together for about $500. The PLC has 24 discrete inputs and 16 discrete outputs.
All thermostats are connected to PLC inputs, all zone pumps and zone actuators, desuperheater pump, water heater, HP start request and reversing relay are connected to PLC output. One of the two loop temperature regulators controls heating and cooling temperature, one loop in the second controls HW heater temperature (desuperheater pump). The thermostats in the HW heater are set to lower temperature than the desuperheater loop therefore the electric heat is always turned off as long as the HP keeps the water hot or anytime when the HP is running. HP starts only when there is a demand for heating or cooling. Switching between cooling and heating mode is automatic. The PLC also controls recirculator of the hot water and turns all pumps on for 1 minute/day to prevent sticking. It also keeps track of number of starts and time running in each operating mode but I didn't analyze that part yet.
Beside relocation of chilled coolant for AC I added ports for possible future heat exchanger to heat HW solely by the HP and use electric heat just in the case HP fails.
Added ports and valves in the HW (desuperheater) loop used for descaling of the desuperheater heat exchanger. Added air trap consisting of 3 feet of vertical pipe Teed to suction of the outside loop pumps. The pipe has a valve in the top to let the trapped air out. It was needed only first few months of operation.
I also installed thermometers on every manifold and pressure gauges to outside and inside loops.
I would make just a guess that the total house electric bill decreased by 20 to 25 USD/motnh (about 10%). 10 USD comes from the heating and 15 USD from HW.
