ReplyOriginally Posted by ThirdCoastAC
....you mean W1 &W2?...... ok i can see your point some what on a straight electric heat that you would want instant heat out of register....but we are talking about heat pumps.... no?....
Professional Member
You can do whatever you want. Most heat strip packages come with one sequencer or contactor for each 10 kw of heat. A 15 kw package would have two sequencers and you can stage them if you would like. The problem we run into is people complaining the air coming out of the vents isn't warm enough so we just wire Y1 and Y2 together in the air handler. Now I'm referring more to strip heat only systems and not so much heat pumps. Even though it is code most existing heat pump systems around here don't have enough power to the A/H to get enough heat strips to stage. The technology is definitely there but the customer usually doesn't want to pay extra when what they had before worked just fine.
Professional Member*
Jason J Saylor
Johnson Controls
"You will encounter many distractions and many temptations to put your goals aside: The security of a job, a wife who wants kids, Whatever. But if you hang in there, always following your vision, I have no doubt you will succeed.”
God Speed, Jim. We'll miss you - 2-26-23
A 5KW rated single phase heater draws between 18 and 22 amps depending on supply voltage at that location.
I work on them.
240 volt 5KW=20.83 amps
240 volt 10KW=41.67 amps
240 volt 15KW=62.5 amps
Of course, very few places have exactly 240 volts. And the heaters resistance will change slightly with the temp of the heater as it varies with air flow. So the amp draw will change also.
Regular Guest
Exactly. You can't get around the physics of it. If your 10 kW strip is only pulling 20A, it is only giving you 5kW of heat unless it is being run at 480v.
The strips are normally 5kW each and more are added to get to whatever total you need.
Lower voltage will give lower amps and you take a double hit on power. As an extreme, say you connected these elements to 120v. You cut the voltage in half, the current is also cut in half, this means that the power (Power = V X I) is cut to 25% of initial value (10kW of elements would produce 2.5kW of heat).
Professional Member*
Sorry man. You are wrong. Ohm's law is correct.
Your memory is close for a 5 kw strip which is what most are. There is typically 4 each 5kw strips in a 20kw package. 2 of these strips are typically energized at a time. More than likely what you are measuring is the amp draw per element, which once again is typically 5kw, not the draw for both elements. It'll come to you over time. You just gotta learn to listen to the old guys. We were in your shoes at one time too!
Professional Member*
lady parts doctor was doing the change due to complaints in the exam rooms. he didn't have any complaints for the heat
Col 3:23
questions asked, answers received, ignorance abated
Professional Member
Yes,you are completely correct. I apologize for my shortness in my prior post. 20A per 5kw, not 10 kw. And I did mean W1 and W2. Long day at work with some very ignorant customers. Not an excuse however for my rudeness.
God Speed, Jim. We'll miss you - 2-26-23
We all have bad days from time to tome. Sometimes you gotta step away from the keyboard for a minute or so before posting.
Some days I take my own advise.
Global Moderator
Wow...........I was beginning to question my knowledge of electric but then i did the math. As stated Ohm's law and between 210-240 volts 41.66-47.61 amp difference.
I read his first post on that and let it go. And as usual you guys would not let it ride. Constant policing here. But thats a good thing. Keep everyone in check.
Good job westval !
Professional Member*
Not looking to keep anyone in check, just thinking outloud through the keyboard!Wow...........I was beginning to question my knowledge of electric but then i did the math. As stated Ohm's law and between 210-240 volts 41.66-47.61 amp difference.
I read his first post on that and let it go. And as usual you guys would not let it ride. Constant policing here. But thats a good thing. Keep everyone in check.
Good job westval !......during heating season that's the only time I get to stop and think.....
Professional Member*
If there is enough amperage to the air handler you could let the thermostat use 10KW for AUX heat and use the other 5KW for defrost. Most air handlers just need a simple wiring change to set them up that way, connect W1 to the thermostat, W2 to the white/defrost from the condenser. If the heat pump can't keep up then only 10KW of heat would be added instead of the full 15KW. If the temp dips too much with only 5KW in defrost the thermostat will bring on the 10KW aux heat for a total of 15KW. Wiring this way has some potential to save some $$$ in defrost at the expense of cooler air from the registers.
God Speed, Jim. We'll miss you - 2-26-23
Old thread, closed as too many previous posters are not Pro * members.
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