Allison: I guess that makes
Allison: I guess that makes sense. I was thinking that 200 Btu/hr was a bit high for direct latent load from an occupant. But 45 Btu/hr/person seems low for showers, cooking, etc. That amounts to 1 pound of water per day per person. Hmmm

Roy, the latent loads for

Roy, the latent loads for cooking, showers, and other moisture-generating activities are built into the 200 BTU/hr latent load that’s assigned to each person in the house.  Manual J says 45 of the 200 BTU/hr covers those things.

David: But you don’t have
David: But you don’t have any other latent loads like cooking, showers, or laundry?

This is a bit off-topic but I
This is a bit off-topic but I’m sure Allison won’t mind 🙂

I didn’t neglect latent loads… It’s shown at the bottom of the report (550 BTU/hr = 800 BTUH for 4 occupants minus 250 BTUH for infiltration). The infiltration is negative because the ASHRAE coincident wet bulb for my location is slightly less than the assumed indoor wet bulb in my model. We typically see condensate during monsoon (July through mid-September).

Regarding ventilation… my house, which tested out at 0.52 ACH50, definitely does not meet ASHRAE 62.2, but that’s another conversation!

Thanks David, those are
Thanks David, those are interesting numbers. My previous house in Texas had a west-facing patio and it was miserable. The house before that in Minnesota had a north facing patio and it too was miserable since the sun moves quite a bit north of west in Minnesota late in the day in the summer time. My current house has an east-facing patio which was a requirement when we were house hunting this time. I don’t think that anyone can deny that west-facing glazing is a disaster anywhere, so thanks for pointing that out. I am glad that Manual J figured out to use hourly window loads. But back to internal loads. It appears that you do not have any mechanical ventilation. Do you know if your house meets ASHRAE 62.2 minimum ventilation requirements? Also, you appear to have neglected latent loads which is probably OK in Arizona. However, I am curious, do you ever see condensate leaving your indoor coil drain pan?

@Roy, I uploaded my home’s
@Roy, I uploaded my home’s load breakdown here: http://optimalbuilding.com/files/kc_williams_rev4.pdf. As you can see, ‘internal’ is 2nd largest component of the cooling load, after windows of course. My windows would have been larger but I have engineered overhangs that fully shade all south glazing in summer, plus I modeled ‘closed blinds’ on all windows that get direct sun, and I only have one west facing window (I put my garage on the west side of the house). Interesting side-note: As of the 8th Edition of Manual J, windows loads are analyzed hourly based on orientation and shading. This means solar gains on east windows don’t directly contribute to a room’s peak load.

MJ recommends 500 BTUH for a laundry (accounts for residual heat from washer & dryer ops, which is fairly conservative) and 1200 BTUH for a ‘standard’ kitchen. I used those numbers plus I modeled 4 occupants @ 230, so internal gains = 2620, or 28% of my sensible cooling load. And yes, internal loads are assumed to be present during peak cooling hours.

David and Allison: This is
David and Allison: This is interesting. I will admit that I have never done a Manual J load analysis. Could each of you take your super-efficient home case and give an actual breakdown of the design cooling loads (Btu/hr, not percent)? As for laundry (washers and dryers), they do consume a lot of energy, especially if you are all electric, but a lot of that energy goes down the drain or out the dryer exhaust, thus is not all internal load. Does Manual J assume that they occur at peak cooling load times?

Avery, yes, the sensible

Avery, yes, the sensible cooling load for this house was less than 11,000 BTU/hr.  The internal gains added up to 3,290 BTU/hr.  We typically use 1,200 for the kitchen, 900 for the living room, 500 for offices and laundry rooms, plus the standard MJ occupant loads.  So in this case, I think we had 1,200 + 900 + 500 + 3×230 = 3,290 BTU/hr, which is almost a third of the sensible load for the house.

@Avery, the largest internal
@Avery, the largest internal loads are typically in the kitchen and laundry (range, oven(s), refrig, dryer).

BTW, my own home, which I completed last year, has a design cooling load of just under 1 ton @ 100F outdoor / 77F indoor. It’s in SE Arizona. I installed a 1-ton Carrier 18VS with four zones. The home has 3,300 conditioned floor area, although part of that consists of a fully-below-grade finished basement, which only has a small cooling load (mostly from egress windows).

I’m curious about the source
I’m curious about the source of these internal gains on your pie chart. Title 24 defaults for half a watt per square foot, so even in a 2000 SF house the default would be 1kW which is all of 1/4 ton. I’m working on my living room setup with a big screen TV and a home theatre sound system on, and the UPS powering all this and my Dish receiver says it’s drawing 200w. My iMac on a different UPS says 56 watts. The “mini-IDF” in the side bedroom, 9 cameras, a Mac mini, and the router is 67W on its UPS. My smart meter is reading nearly 800w right now, but I think most of that is not an internal load because the hot tub’s pump is running presently. I do have the lights off, but they’re all LED, so even having several of them on would add 100-150W at most.

So are you showing us a house for which the total cooling load is sub-ton?