I'm trying to evaluate a daily energy saving in emoncms. I have 2 heat exchangers on my hot water system to recover waste heat from showering. (Called Recoh-vert's)
Theoretical energy required to heat water is :
Volume x delta temperature x Heat Capacity of water (4.187) [totalised over a day as KW]
from this I want to deduct actual power consumption of the Electrical hot water tank [totalised over a day as KW]
and I hope to be left with a figure that is the saving as a result of the heat recovery.
So with that as a theory, my setup is 2 EmonTx's one at the cold water input with a single temperature feed, and another with Hot water output temperature from the tank, ct&Vac for heating power and a pulse counter input from a water flow meter rated at 20 pulses per litre.
Assuming my other recent post can be answered about totalising daily water volume using KWh/d, I have 2 questions:
1. Can I multiply daily figures together? I need to multiply daily volume by daily delta temp (handily max&min functions in emoncms are daily) by a constant of 4.187, then subtract a daily power.
2. and as a final challenge, is there any way of using yesterday's value as opposed to today's? My hot water is set to turn on at 1am to heat he tank up on cheaper electricity overnight!
Re: Emoncms: Calculations on Daily Figures & Daily pulse count
So, having thought long and hard... (Sadly just as I'm about to fall asleep, these things come to me!):
1. Get the emonTX to send litres per second multiplied by 4187 (the HC of water in J, not KJ) - this makes the integer maths better at the litres/second is likely to be about 0.2 max, which isn't very integer friendly. 1J/s is a Watt
2. In emoncms:
a. subtract cold from hot
b. multiply by 0.01 (for deg C)
c. Max value it [the sensors take a few minutes to get an accurate reading of the liquid temperature in the pipe as they're thermally bonded to the outside of the pipe, so Max will get this to be close enough]
d. multiply by the (litres/second x HC) input
e. Log if required as Shower energy consumption (instantaneous in Watts)
f. deduct power (ct x volts) from tank [this will be a big +ve number when the shower is on, then when the power to the tank comes on at 1am, the number will be very big -ve
g. [hopefully] kwh/d function will give a small +ve number daily representing the saving in units per day after it has integrated the +ve and -ve numbers
3. if I set the timezone so that the daily counters roll over at 6am then that might allow yesterdays's water heating to be totalled with the electricity used by the tank in the small hours of the morning..?