Control motor speed?

[Sizz]

I'm leaning towards ditching the HLT entirely. The plan is to use a RIMS style electric heater as an inline tankless heater which will supply strike and sparge water at the desired temperature automatically. One possibility is to control the flow manually via ball valve and have the electric element under PID control. This seems fairly straightforward and one disadvantage is possibly limiting your throughput by having the valve unnecessarily closed too much. The other option is to have the element full on and control the flow, either by pump speed or valve control. Can you hook up an SSR to an AC motor and modulate it via PID like the heaters? I know it works on dc motors.

[rmcghie]

For a 10 gallon batch with 20 pounds of grain at 1.25 quarts per pound, you will need 25 quarts of water, which will weigh approximately 50 pounds. To raise the temperature of this much water from say 65F to 165F will take (50x100) or 5,000 btus. At 50% efficiency a 100,000 btuh burner would take 1/10 of an hour or 6 minutes to heat the water. So far OK. However, a 100,000 btuh burner is a damn big burner and I think you will have substantial difficulty trying to build a 50% efficient water heater to heat such small quantities of water. If an electric element is used instead and assuming 100% efficiency it would take a 17570 watt element to heat the water in 6 minutes. At 240V this would take a 75 amp circuit. With a 4800W element (240V @ 20A) it would take 22 minutes to deliver the 25 quarts of 165F water, assuming that there was no heat loss while you waited the 22 minutes. Stay with a HLT.

[Sizz]

I did calculations based on a 5500w element and got similar results, 17 minutes (math at the bottom). Since the water is directly heated in a small insulated vessel, efficiency should be high. Hopefully, the only significant loss would be the heat absorbtion of the mash tun which is compensated for by overshooting the temperature and rercirc heating during the HERMS mode.

I don't quite follow why you recommend a HLT. Are you saying 22 minutes to heat strike water takes too long? I'd still have to wait that long for the HLT to warm up. If anything, inline heating of the water is more efficient because I don't have to heat up two vessels. Heat loss during the fill up is easily corrected since the system will be hooked up in HERMS mode after the mash tun is filled. Recirculation is started and dough in won't occur until the water is at temperature.

My main concern is if this heater can supply sparge water consistently and at an appropriate rate. Fly sparging is supposed to be a slow process anyway (quart per minute max - palmer). I'm hoping the PID control will keep the temperature consistent.

Code: Select all

Heat capacity of water is 4.184 joules per ml per deg K

25 qt * (946.353mL/qt) = 23,659mL
delta K = 347.039K - 291.48K = 55.56K

power required = 23,659mL * 4.184 j/mL K  * 55.56 K = 5.5e6 joules

1 joule = 1 watt second so for a 5500w element:

time= 5.5e6 watt-seconds / 5500 watts = 1000 seconds = 16.7 minutes

[Backyard Brewer]

There was a thread on HBT about a making an instant heat hot water heater. The basic idea was to cut the bottom off of a cornie keg, removing all the rubber and stuff a dual coil of copper tubing into it and place a propane burner at the opening. The cornie just acts as a chimney of sorts and concentrates the heat on the coils. His initial tests could produce near boiling water by adjusting the flow rate. Obviously great care had to be excercised around the device to keeo from getting burned but it sounded like it showed some promise.

As far as modulating an A/C motor; unless they are made to be variable speed, A/C motors do not like to be varied. If you reduce the voltage to one you'll burn it up. The voltage drop causes a current increase which causes a heat build up that'll kill it. I don't know about modulating it with a PWM type circuit but I doubt that would be good for it either. A proportional valve on a mag-drive pump would probably be your best bet, or go with a DC current pump. One of my buddies uses the ShurFlo RV pumps. They're food safe, rated to 170* and 12VDC. They draw about 8 amps though so you need a pretty good power supply for them.

Derrin