politics123
Active Member
Hi Experts --
So, I have a solar H/W heater on order, and as I was buying all the parts, I got to thinking: "Why should I pay $150 for a differential controller, if, my Elk M1 can probably do the same work." I was hoping someone could double check my work/RP rules or point out any gotcha-s.
A Solar H/W differential controller measures two temperatures: at the solar panel, and at the storage tank. They are simple devices that turn on an electrical outlet (eg: for a water pump) when the temperature at the flat-plate collector ("panel") is ~10 degrees hotter than the water in the tank. It turns off the electrical outlet when the temperature at the panel is only 5 degrees hotter than the tank. They usually have two additional rules:
1) don't turn on (or turn off) when the panel is below a set limit (eg: below 90 degrees)
2) don't turn on (or turn off) when the tank is already super-hot (eg: above 140 degrees)
The way I thought to solve this:
Get the temperatures
I think: Every 2 minutes, I'm going to check the temperatures. Every four minutes, I'll either turn the solar HW system on or off, depending on the conditions.
Cost savings ($190 for differential controller + probes) + power to drive
Costs: (unknown) for relays and Elk temperature probes.
Advantages: I can turn the system off/on remotely, I can also purchase a 30amp relay for the H/W heater's heating element and have the two interact (eg: don't turn on water heater burner if the solar portion is operational)
Disadvantages: I can't think of any
Thoughts?
Issues:
I need a couple inexpensive relays and temperature probes.
-- I know Elk sells a 9100, but I don't need/want X-10 control. Anyone recommend a couple 120VAC (5-10amp) relays that can be driven from an Elk Output?
-- Any news on when the Elk 1-wire interface will be released? Other options? (the sensors have to measure the temperature of water in a pipe, and as long as they can measure the temperature of a pipe, I'll be okay)
So, I have a solar H/W heater on order, and as I was buying all the parts, I got to thinking: "Why should I pay $150 for a differential controller, if, my Elk M1 can probably do the same work." I was hoping someone could double check my work/RP rules or point out any gotcha-s.
A Solar H/W differential controller measures two temperatures: at the solar panel, and at the storage tank. They are simple devices that turn on an electrical outlet (eg: for a water pump) when the temperature at the flat-plate collector ("panel") is ~10 degrees hotter than the water in the tank. It turns off the electrical outlet when the temperature at the panel is only 5 degrees hotter than the tank. They usually have two additional rules:
1) don't turn on (or turn off) when the panel is below a set limit (eg: below 90 degrees)
2) don't turn on (or turn off) when the tank is already super-hot (eg: above 140 degrees)
The way I thought to solve this:
Get the temperatures
- Whenever every 2 minutes, get the temperatures from the panel and tank. Store the temperatures into counters and increment two counters to reflect +5 and +10 degree variables.
c_waterheater=temp_waterheater
c_waterheater_10 = temp_waterheater
c_waterheater_5 = temp_waterheater
c_panel=temp_panel
c_waterheater_10 += 10
c_waterheater_5 += 5
Toggle Output 208
- Whenever Output 208 is on
and temp_waterheater < 140 degrees
and temp_panel > c_waterheater_10
and temp_panel > 90 degrees
THEN turn on solar pump (output 207)
- Whenever Output 208 is turned off
and output 207 is turned on
and temp_panel < 90 degrees
then turn output 207 off - Whenever Output 208 is turned off
and output 207 is turned on
and temp_waterheater > 140 degrees
then turn output 207 off - Whenever Output 208 is turned off
and output 207 is turned on
and temp_panel< c_waterheater_5
then turn output 207 off
- Whenever Output 207 is turned on
then turn output 206 on for 1 minute - Whenever Output 207 is turned off
then turn output 206 off
I think: Every 2 minutes, I'm going to check the temperatures. Every four minutes, I'll either turn the solar HW system on or off, depending on the conditions.
Cost savings ($190 for differential controller + probes) + power to drive
Costs: (unknown) for relays and Elk temperature probes.
Advantages: I can turn the system off/on remotely, I can also purchase a 30amp relay for the H/W heater's heating element and have the two interact (eg: don't turn on water heater burner if the solar portion is operational)
Disadvantages: I can't think of any
Thoughts?
Issues:
I need a couple inexpensive relays and temperature probes.
-- I know Elk sells a 9100, but I don't need/want X-10 control. Anyone recommend a couple 120VAC (5-10amp) relays that can be driven from an Elk Output?
-- Any news on when the Elk 1-wire interface will be released? Other options? (the sensors have to measure the temperature of water in a pipe, and as long as they can measure the temperature of a pipe, I'll be okay)