Advice Sought for a High Performance New Construction in Houston
My wife and I are in the early phases of designing a new house in Houston. We have started working with an Architect, and we hope to engage a builder here soon. I've spent about three years reading and getting educated on building practices and energy efficiency (e.g., I have read a lot of what Joe Lstirubek has written), and I would appreciate getting some advice from the Pros here before we get too much farther along with the design and to help educate me about how to know when I've got a great HVAC contractor vs. when I've got someone who knows enough to put the right words on the bid, but whose team does the same-old-thing when it comes down to installation.
Some quick project "specs" (goals, really):
- Tight construction - hopefully ~1ACH50, my limit is 2.0 ACH50 -- think "quality" and "attention to detail" here, not just "energy savings".
- Lots of glass, and, unfortunately, a lot of it West-facing (SHGC will be <0.25 for these, hopefully <0.20) due to lot orientation and building setbacks.
- ~3,000sf on 2 levels - public spaces downstairs, private spaces upstairs. We will most likely want at least 4 zones.
- We will probably have a high reflectivity and high emissivity roof, but that is probably for a different discussion (e.g., energy savings vs. damage resistance/durability vs. lifecycle costs)
- DHW will most likely be gas - either tankless or something like an AO Smith Vertex 100
- Man J and Man D will be a must.
We will have a big challenge with heat gain from the western afternoon summer sun (overhangs only go so far and no trees on that side yet), but the rest of the day should be fairly moderate. As I understand it, we will have two basic paths to consider for HVAC, each with advantages and disadvantages:
- Air Conditioner and Gas Furnace
- Heat Pump (little need for 'emergency' heat given the market and our climate)
The Air Conditioner + Furnace option will be standard construction for a lot of Houston homes, so it should be relatively cheap. However, the gas furnace isn't free, so the heat pump might have all-in costs that are lower, plus a heat pump saves me a roof/wall penetration.
Further complicating the picture is the need for dehumidification and fresh air intake. We can go with an ERV or a damper for the air exchange, but the more interesting question (to me) is whether a VRF or other continuously variable system will eliminate the need for a dedicated dehumidifier, or whether we would still want a dehumidifier even with a system like a ducted/split Mitsu VRF, Carrier Greenspeed or Lennox XP25.
For t-stat, I'd like to be able to change the temperature setpoints from a phone/tablet while we are in the house, rather than have to get out of bed, but I also hate the idea of having to pay a subscription charge to do this.
I'm willing to pay for performance (comfort, control), but I don't want to overpay, and I am especially concerned about paying for anything oversized. Since some of these options are manufacturer-specific, that will need to inform which contractors we ultimately look at when we get to that point. However, for now, I want to be sure that we are asking the right questions in the right ways.
Thanks for any thoughts!
FIRST , APPROXIMATE MANUAL J
High Peak HEAT GAIN may not even be a significant issue
Originally Posted by Bear_in_HOU
MAYTAG or Carrier Greenspeed obviously deserve consideration
( although that may lead you to one unit with Several zones).
Houston ~3,000 SF on 2 levels
House dimensions : 52 x 30 ?
T-stat set Winter 72'F ___ Summer 76' F __ ?
Wall _ R-15 __ ?
Ceiling R-30 ___ ?
U-value _ 0.40 ?
S.G.H.C. ___ 0.37 ?
_______ Window Areas
____ First __ ... _____ Second
____ Floor __________ . Floor
Total 260 ? _________ 170 Sq Feet ?
N _______ ,,,,,,,, ______ Sq Feet
S _______ ......... ______
E _______ ------ ______
West ____ __ __ - ______
A.C.H. 0.2 (air change per hour)
Minimal duct heat gain even at R-4 or so.
Supply Air 54'F