Residential One-Family dwelling Calculation

[tadavidson]

Hey Guys I'm trying to do a service calculation for a new home 3498 heated. It has two 3 ton heat pumps with 10 kw heat strips, The owner wants two water heaters in series (thats my first request for this I'm curious).. I came up with 384A. I've not calculated one in a while, accustomed to smaller homes 200A will cover.

 

[bob]

Hey Guys I'm trying to do a service calculation for a new home 3498 heated. It has two 3 ton heat pumps with 10 kw heat strips, The owner wants two water heaters in series (thats my first request for this I'm curious).. I came up with 384A. I've not calculated one in a while, accustomed to smaller homes 200A will cover.

Section 220 is your instructions. You need to know the sq. footage
and the other loads. This location has a caculator to check you caculations.
I have 2 wh in my home. Usually one is at the bathrooms and 1 in the utility/kitchen area. It saves
you from hauling that hot water across the total length of the house.
http://www.electricalknowledge.com/SFDLoadCalc.asp

 

[tadavidson]

Thanks for the response Bob War Eagle. Great tool at that site. I still uncertain about a couple of items. Have you ever heard of connecting water heaters in series? Would you think both heat pumps would be added heat and A/C. Why do you think the bath rooms require a dedicated circuit for each but then are not calculated an allowance?

Series I took meaning electrically?

 

[MAS2006]

Suggest on demand unit instead, they last longer and save on your energy bills. I heard of using solar water heater to preheat supply to water heater.
Find out the reason he wants it hooked up this way. How far are the points of use from water heater location? Small on demand units are available for example remote bathroom locations.

 

[bob]

Thanks for the response Bob War Eagle. Great tool at that site. I still uncertain about a couple of items. Have you ever heard of connecting water heaters in series? Would you think both heat pumps would be added heat and A/C. Why do you think the bath rooms require a dedicated circuit for each but then are not calculated an allowance?

Series I took meaning electrically?

Heat Pumps can run both the compressor and electric strip heat at the same time.
210.11(C)3 requires a seperate ckt for the bathroom.
As for connecting the water heaters in series, I don't understand the queston. You need a ckt for each WH.

 

[haskindm]

You would not hook the water heaters in series electrically. Each will need a dedicated circuit. The water heaters would be plumbed in series. The second water heater would receive water that had already been heated in the first heater and would just maintain the temperature. I agree that a better solution may be several on-demand heaters.

 

[bthielen]

An off-peak electric hot water system typically requires one of two options. 1. Two water heaters connected in series to provide a minimum 100 gallons of hot water storage.

2. One water heater set to very high temperature and a mixing valve on the heater's output to temper the water to a safe level.

Perhaps this is why they request two heaters.

Bob

 

[tadavidson]

Why do you think the bath rooms require a dedicated circuit for each but then are not included as others (microwave )calculated seperately in the total calculation? With the use of hot curlers, blow dryers, shaving creme heaters, small space heaters (many women like them in the winter) possombilly used at the same time. 4 baths with a powder room.

 

[haskindm]

The "load" for the bathroom circuit is included in the 3VA per square foot calculation that is included in all residential calculations. There is no fixed load in the bathroom that could be figured like there is with a microwave. The loads that are used are of a limited duration. I believe the 20-amp requirement was an attempt to reduce nuisance tripping. This is a design issue and probably should not be part of the NEC (my opinion, and certainly open to debate). The single 20-amp circuit serving multiple bathrooms may still not be adequate, but then the NEC does not promise that an installation is adequate, only that it is safe - see article 90.