Letter I hate having to send (leo g)

leo g_13

that lately our company has been called upon to try to "rescue" some homeowners poorly installed systems. these systems have been installed by "professionals". here is the latest letter that i just sent out. OUCH!


"Dear E####,
I have some questions regarding the heating. Do you have a gas line (either propane or natural) for your house? Do you know the total amperage that you have in your electrical service?

I have run the heatloss numbers every wich way but loose, and there is no way that the system as installed can heat your home during cold weather. I am sure that you know this as you experienced this for yourself this past winter. What I have come up with is on the design day, which is the estimated coldest day of the year, your home would loose about 90,000 BTU's per hour. The system as installed (I am assuming that it is installed to RHWHA guidelines), can only produce about 62,000 BTU's per hour. Leaving a deficit of roughly 28,000 BTU's per hour. The electric heater that is installed presently, according to the manufacture, can produce about 48,000 BTU's per hour, or just a bit better then half of what is needed for design day, let alone less then what the tubing in the floor could hypothetically release.

By my figures, we would need to have another 5.6 Kilowatts of heat energy installed for the main floor solarium and 2.2 Kilowatts of heat energy for the top floor great room as supplemental heat to be able to keep your home warm during design days. All in all, i estimate that it would take about 130-140 amps of electrical energy to sufficiently heat your home on design days. Right now you are using about 75 amps of electrical energy. This is why I am wondering about the size of your service, or if you have any type of gas available.

I will be talking with my electrician friend in the next few days, and will pick his brain to see if there is some sort of "magic" that he knows of, but please don't get your hopes up. Sorry to be the bearer of sad news, but let me delve further to see if we can find a way out of this situation.

yours sincerely,
Leo Galozo,
NRG Hydronic Technologies"




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DaveGateway

Is that amp figure right?

2.2KW= 2200 watts/120 volts = about 19 AMP
5.6KW= 5600 watts/120 volts = about 47 AMP

jim lockard

I don't know

2,200 watts divided by 240 volts =9.16 amps 5600 watts divided by 240 volts = 23.33 amps 9.16+23.33 = 32.49 amps @ 240 volts. 1 watt = 3.41 Btu's so. 90,000. Btu's divided by 3.41 = 26,392 watts.
26,400 watts divided by 240 volts = 110 amps @ 240 volts.
lets see what others think. J. Lockard

Steamhead

Leo, I don't mean to nitpick

but when writing to customers, we really need to check spelling. For example, in "your home would loose about 90,000 BTU's per hour" the correct spelling is "lose". And in "according to the manufacture", it should be "manufacturer". A spell-checker would not normally pick these up since the spellings you used would be correct in different circumstances. I've actually won jobs when lower bidders have misspelled words like that.

Dan wrote something called "Quote with lots of paper" which emphasizes the value of good presentation- I'll let you all know where it is when I find it, if someone else hasn't found it first.

Oterwise, yor leter iz verry wel ritten.

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leo g_13

Thanx

you're right on! and to think that i went over that letter about four times before sending it! DOH!

leo g

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leo g_13

yes,

but i was adding the extra 20% for the right size breakers. I was taught that the load should be 80% of the breakers capacity.

leo g

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jim lockard

Now Leo

We are not talking about the over current protection or the wire size or the electrical load calculation of the home or derating. We are discussing the POWER consumption of 90,000 BTU'S
Leo I understand you can divide the load as you wish
and the power consumption will still be 90,000 BTU's Best Wishes J.Lockard

Lurker_2

you know

> you're right on! and to think that i went over

> that letter about four times before sending it!

> DOH!

>

> leo g

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 286&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_



I can't read well on the screen. I always have to print it out to see stuff like that

Lurker_2

you know

I can't read well on the screen. I always have to print it out to see stuff like that

Steamhead

Maybe it's your monitor

About a year ago, I upgraded to a Sony 18-inch LCD unit (which was a display model selling for half the cost of a new one) and realized it was a lot clearer than the CRT unit I had before. It is also much easier on my eyes, though part of that is due to its increased viewing area. You might want to test-drive one at your local computer or office-supply store. Sony units tend to be quite good- also expensive, but sometimes you can find one on sale like I did.

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Matt Undy

Branch VS Service

That is conductor sizing for a branch circuit. The Capacity of the circuit for a fixed load must be 125% of that load (for a resistive load, its more complicated for motors). The service capacity doesn't automatically fall under this restriction. It is more complicated based on intermitent and continuous loads and i'm not sure which electric heat would be. An electrician would have to figure what the service can handle. BTW I'm not an electrican, I am just an EE that has done enough reading of and about the NEC to do my own work. I can recommend and excellent though slightly dated book if you would like.

Matt

Unknown

though

Before you splurge on a new monitor, maybe try increasing your monitor's resolution and refresh rate (the XXhz number). Refresh should be over 80 to be easier on the eyes if possible.
_______________________________

Northeast Radiant Technology, LLC

Robert Brown, Co-Owner, RPA certified Radiant Designer

207.899.2328
NRT@maine.rr.com

scrook_2

in kW

90,000 BTU/hr divided by 3413 BTU/hr per watt = 26.4 kW or 26,400 Watts. Dividing by 240V = 110A. To supply a 110A load the circuit size needs to be sized 1.25X load (1/.80) or greater than/equal to 137.5A therefore a 200A service would be marginal at best.

He has to supply the ENTIRE heating load, not just the deficit of 7.8kW (26,600 BTU/hr), elsewhere sited as about 28,000 BTU/hr -- close enough either way.

If he has, or can install, an alternate fuel (NG or oil or LP) then the electrical service size may not be an issue.

In practice the added electric heat, if baseboard or radiant woul dbe distributed over several smaller 240V circuits (though th etotal power is the same and the 80% of circuit overcurrent device rule still applies. 240V os th eonly way to go, except for VERY small loads, as the cost of a 2 pole breaker over a 1 pole is negligible but the cost of larger gauge wire (possibly even oversized on very long runs to meet voltage drop limits) is not; though again is makes no difference to the required service capacity. If the added electric heat is an electric boiler or furnace then a single large circuit would be req'd (say a 50A breaker & 6 AWG copper for a 8.2kW/28,000 BTU/hr circuit drawing 34.2A at 240V or for a 7.8kW/26,600 BTU/hr circuit drawing 32.5A at 240V. in both cases a 40A circuit breaker is slightly too small to meet the 125% requirement.

Matt Undy

NEC Service Calculations

Here is what I get using the NEC. I assumed it had an electric dryer, range and wter heater if it didn't have some from of gas available. The water heater load can come from the nameplate rating, the ones labeled "NEC Minimum" must be at least that. The square footage may be changed based on actual size. Other large appliances or motors woudl ahve to be added. AC wouldnt' be included becuase it woldn't be used at the same time as the heat and the heat is the larger load. The 80% of rated ampacity is for continuous loads. The total load for a residential service may be 100% of the rated ampacity of the conductors but the continuous loads may be no more than 80% of that total. A continuous load is a load that continues for 3 or more hours.

I used the common service laod calcualtion method. Some of the optional methods may work out to a smaller service size. There may be some exceptions or demand factors for electirc heat since it is only a continuous load on design day. The reason that continuous loads are restricted to 80% of circuit ampacity is to protect devices and terminations from constant heat from the load. If this only happens a few times a year it probably isnt'a probelem. You would need an electrician that knows the codes for service sizing and electric heating very well to properly size the service.

(this was a nice table until i posted it..i can e-mail you somethign formated nicely if you want).

Load Power (w)


90Mbtuh 26358

kitchen 3000 NEC Minimum

laundry 1500 NEC Minimum

1500 ft^2 *3w/ft^2 4500 Assumes 1500 ft^2 home

dryer 5000 NEC Minimum

range 8000 NEC Minimum

water heater 3500

total 51858 Watts

216.075 Amps

leo g_13

i finally

talked to the clients sparky, and he feels that the 200 amp service will be fine. so now onto the design /quote phase. as the basement is in-slab and the main and upper floors are in-joist, i am leaning towards 2 boilers to keep the control part simple and less expensive.

leo g

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MikeB34

What are you

Using? electric boiler? If so check out Argo technologies new AT.

Mike