[constantinople]

We are building a 4800 sq. ft. home with divided living spaces (generational home / elderly parents on one side, immediate family on the other). We have two master bedrooms, two kitchens, etc. We had planned on two traditional forced air systems with separate thermostats, originally located in a crawlspace. However, after seeing the cost of the crawl space, we thought of removing it from the plan, but in doing so we will have some challenges in bridging some of the vaulted ceilings where there is no attic space above. Some of the ideas suggested seemed kind of unsightly to me. This involved a self-supported duct bridge across the area that says light-well in the plans. I wondered if there was another way to overcome this situation -- such as with a ductless system. When I suggested it to my GC, he felt, while theoretically efficient, the individual units / zones would not provide enough heating in the winter. He suggested a zoning system with dampers as another option.

So…what about a ductless solution? Do people choose to install mini split systems (Mistsu Mr. Slim, Fujitsu Hybrid Flex Inverter, etc.; Daikin is not availably in my area) in new construction? I have seen lots of discussion in remodel / old construction applications, but not too much about new construction applications.

What about other solutions? I am all ears...

Suggested systems we were planning to install is:
1 RUUD 90K BTU, 4 ton, 13 seer
1 RUUD 60K BTU, 3 ton, 13 seer

A heat pump upgrade was optioned.

Any thoughts would be appreciated.

Thanks

 

[constantinople]

Well...I was hoping someone would throw in their two cents...!

The GC and I met with the HVAC Contractor yesterday and he brought up a Unico system as a possible solution to our architectural situation. If anyone has any thoughts, I'd love to hear them.

 

[Crazy4thenucks]

The best thing for an open concept design IMO is to have everything in a crawlspace inorder to keep the open concept feel. Now there is the posibility of going with a variable refigerant flow system that can heat/cool at the same time. LG and Mitsubishi have these type of systems. Basically you have a choice of head unit and how many zones you have. Keep in mind the upfront cost of these units is not small.

 

[energy_rater_La]

the crawlspace issue is climate dependent.
I have a client in north Louisiana who used the
unvented crawl as supply plenum..too many details to go into
but if properly done...it works well...vapor barrier lots of air sealing details.
other than his install...ductwork in crawlspaces are difficult to install
often are not well sealed and literally suck dirty moist air into ducts
and the distribute throughout your home.
mechanical install in crawlspace is more difficult than ducts...look
at size differences!! ducts are much smaller and flexible than equipment.


where are you located OP? climate matters.
it just seems to me that building a new house
13SEER is the least efficient equip made. why cut corners there
for something that effects your comfort every day.
when you upgrade to 16 SEER and above you get into variable speed
and two stage world. these systems operate much better
as when house is not in full use system operate in lower speed
for lower operating costs..and improved efficiency.
but when house is busy...higher speed will be able to keep up with
comfort.

are you all electric? if so look at hi eff heat pumps.
electric and gas...increase efficiency of both.

you are at the best stage to make these changes, ask these questions
and learn what will work best for you.
hvac contractor should be bidding good...better...best bid.
13 seer 16 seer 18 seer for example.
ask for this.

just food for thought...
you shouldn't have to suppliment with minisplits.
not on new construction

best of luck.

 

[constantinople]

We had planned to go the crawlspace route, but reconsidered, primarily for cost concerns. The cost benefit ratio seemed a little out of whack, so we went back to a monolithic slab. In doing so, we also were forced to reconsider the HVAC component.

The build is in mid-Missouri, so we have some substantial seasonal temperature swings: from zero in the winter to low 100s in the summer.

We will have gas service.

I will ask for some bid variables as suggested, and see what is proposed. But we still have the issue of an open floor plan with no where to put duct work. Perhaps we should go with our original plan and do a sealed crawlspace.

 

[energy_rater_La]

concrete block build??
stick build, sips or icf?

 

[DavidNJ]

First: Where is the house?

Second: Which way is south?

Third: What are you objectives: comfort, operating costs, installation costs?

Fourth: What are the rates (including delivery and other charges) for electricity and natural gas, if available?

Fifth: What is the current state of the construction? Is it started?

Sixth: What is the type if environmental sealing used? Is the attic sealed or vented?

As a general note, it would seem from most research a lot of heating system efficiency is lost in the duct work, both air and thermal leakage. As far as HV systems (and Unico is not the one I'd choose), you may find this interesting:http://www.akduct.com/

 

[constantinople]

The house is stick built.

David:
1. The house is in mid-Missouri
2. The front of the house faces south.
3. Objectives in order are: #1 - comfort, #2 - op. costs, #3 - installation costs
4. Not sure, but can check into it.
5. Construction has not started.
6. Attic is vented.

If not Unico, then what? Thanks for the link to akduct.com -- it is interesting.

 

[constantinople]

I went and pulled some bills…not sure what this stuff means:
RDG: 3581, Prev. RDG: 3560, Use: 21, Actual Reading, Rate: RS GS P, Amount: 34.99

Electric:
Present Reading: 58695 KWH, Prev. Reading: 56956 KWH, Usage: 1739 KWH, Amount: $201.49

Hope that helps.

 

[DavidNJ]

That would be expensive gas and relatively cheap electricity.

The system you listed seemed pretty basic. How big is your budget?

I'd pay attention to the ducts first. There will be a lot of different opinions here. Net, you duct losses can be much greater than the difference between an 80% and 95% AFUE furnace and a 13 and 16 SEER A/C.

What windows are you using and what type of wall and ceiling construction?

 

[egads]

As a homeowner and not an HVAC pro, I would take to heart the advice to spend extra now to get the HVAC right. I would be worth having a duct designer look this over rather than have some in house person at the architects office design this. Even if i had to give up some higher end finishes that could be upgraded later. This forum is full of homeowner posts trying to find solutions to bad design. Energy is only going get more expensive.

And as a complete aside, the master closet in A would work better with a pair of pocket doors back to back. You will gain another whole wall of hanging or shelving.

 

[beenthere]

Might want to reconsider that crawlspace.

Do homes in your area sell better if they have a crawlspace, then if they are on a slab. or doesn't it make a difference.

The money you save today, may cost your more tomorrow.

 

[constantinople]

David,

2x6 exterior wall construction, 2x4 interior with drywall (did consider blue board with veneer plaster). Exterior will be hardcoat stucco in a traditional three layer application.

Windows are Andsersen 400 vinyl on wood.

Budget is always a concern, but if the benefits are substantial, we can manage it. Problem is that standard basic systems seem to rule the day in this area and I am not hearing much else. I went over the akduct site pretty thoroughly and can see some substantial benefits with that sort of system, but I am quite sure I won't find anyl installers familiar with it. I guess I can be a guinea pig...

I have another appointment this AM with a different contractor who comes recommended for challenging installs...any advice on what I should be asking for or material suggestions? I want a good system, but I am not knowledgable enough to request specific products or systems.

Thanks for all the feedback.

 

[energy_rater_La]

16 seer variable speed
with 96% gas 2 stage.

R-8 ducts..put in attic rather than crawlspae.
get manual j for sizing
have duct system designed and sealed.

ask for good better best pricing/bids.

best of luck

 

[DavidNJ]

Question: has the design heat loss and heat gain been calculated?

 

[constantinople]

I am not sure if a heat loss / heat gain has been calculated. I will have to check into that. If so, what I am looking for?

 

[energy_rater_La]

manual j

 

[DavidNJ]

manual j

Elaborating on that there are two types of programs: one that calculates the maximum heat loss and heat gain (in btu/hr) for your climate and one that calculates that plus the actually energy usage over a year in your climate. The advantage of a dual fuel hybrid (gas furnance and heat pump) or thermostat setback would showup in the second but not the first.

The Air Conditioning Contractors Association (ACCA) has a specification, Manual J, for calculating the design limits for residential structures. Its latest version, Version 8 often abreviated MJ8, can only be done with a computer. There are three certified programs to do that calculation; your HVAC contractor and maybe you GC should have one and have done it on the design of your house.

There are others, older versions of Manual J and from the Institute of Boiler and Radiator Manufacturers (IBR). Of these, MJ8 is the most sophisticated.

California has its own program requirements that insure compliance with Title 24. Different and a bit more comprehensive.

Larger buildings have a more comprehensive program that models energy usage. They are typically used on commercial buildings. They include Carrier's HAP and Trane's Trace. Another, from the Department of Energy and free, is Energy Plus. There are older ones such as DOE2, Blast (both incorporated into Energy Plus) and Energy Pro (commercial product). I'm learning Energy Plus, but it can take a while.

Most likely your HVAC contractor doesn't use that type of program and may have never heard of them.

The design load is necessary to answer the question how many systems and what size. It can indicate if zoning is beneficial and how the zoning should be configured. The energy use modeling programs would be necessary to answer the question is SEER 16 cost effective vs. SEER 13, but there rules of them for your region are probably close enough.

Your energy costs should be rechecked. At 11¢/kwh and over $1.60/therm, a dual fuel hybrid would definitely be an advantage. However, their cost effectiveness is dependent on the efficiency of the condenser.

You have a room labeled 'chapel'. If you are going to have lots of people in that room your heating and ac needs, at least for that area, could be different than a regular residence. It could require cooling when other parts of the house require heating, require more removal of latent heat (moisture) relative to sensible heat (temperature), and higher ventilation needs. That would be more a commerical system than a residential.

If you have commercial or commercial style cooking equipment, possibly to serve larger groups, you could have a requirement for make up air. In your climate, that air would have to be conditioned (heated or cooled) in the winter (in which case it is heating).

On the basics, duct efficiency could be important in delivering it. If it needs to accomodate larger groups, the budget implied in the two builder grade residential systems could too small, possibly way too small.

 

[constantinople]

David, thanks for your comprehensive post. I hadn't really thought about the chapel area possibly needing supplemental cooling to accommodate a group. Obviously I need to continue my discussions with the contractors.

I did ask about the Manual J load calculation and I was told 8.8 tons. But, how can one tell if the number is correct without doing it yourself?

 

[DavidNJ]

You need a heating and cooling from the MJ8. You also need it room by room, and ideally with a knowledge of what the biggest issues are in each room. For example heat gain can be radiant from windows. Heat loss can be though a fireplace. And of course, 40 people seated for an hour is a heat gain.