HVAC question...or two

[hunterdan]

HVAC wisdom needed.

We are at the point of doing HVAC and just thought I'd see what peoples thoughts are regarding our current plan.

After doing a good bit of reading reviews and searching HVAC forums we have decided we like the Bosch system.
Home is a single above grade floor with vaulted ceiling (17') and a walkout basement with open stairway between upper floor and basement.
Bosch offers an inverter compressor heat pump in a 3 or 5 ton unit.Basically, the system does not run wide open when operating if not needed. It runs at a variable speed depending upon demand lengthening life of components and reducing energy demand. The contractor I'm planning to use plans to put the air handler/return above our closet upstairs. It will be a dual zone/split system with electric doors to upper and lower floor ductwork via upper and lower floor thermostats.
I know that every home needs calculations for "R" factors for walls,windows...but with the Bosch 3 ton unit it works with any home needing 1.5-3 ton unit. Mine needs about 2.5-3 so it will be the 3 ton.
My main concern now is that the contractor correctly figures the cubic feet per minute and such for each room or living area and the correct placement of the return.
He says he plans to install one return upstairs. It will be about 2/3 up the 17' vaulted wall dividing our living room from our bed/bath area. He also plans to install the registers for heating/cooling on that same wall....one about 8' away on each side of the return and a few feet lower on the wall.
Here's a link to a thread here on the forum which better describes the home
House build start to finish

Reason for one return is that the stairway is open to the basement

Any opinions appreciated as this system will be installed next week.

Thanks, Dan

 

[CasterTroy]

Need a little more info

What's the CFM per sqft you're dumping into this spaces? What size diffuser per drop? Drum diffuser? or simple 2-way? What's important is throw. If the diffuser just pukes out air it will short-cycle and you'll have issues in cooling in the summer, and in winter you'll have massive cold spots. Where the diffuser washes is important. Is he aiming for those big windows?

I know that every home needs calculations for "R" factors for walls,windows...but with the Bosch 3 ton unit it works with any home needing 1.5-3 ton unit.

More to it than that (of course) Keep in mind if the unit is oversized then you've created a humidity problem as it's cycling on and off constantly.

Ideally you want a unit that's JUST capable of meeting design day requirements....because you'll ONLY see those design days 5-20 days in a whole year, so the REST of the time is shoulder cycle.

Not a residential expert, but I've stayed in a residence overnight so maybe a little has rubbed off on me.

 

[hunterdan]

Yep, he is supposed to start figuring the cfm's tomorrow. Not sure about drum or 2 way diffuser but I'll check. Supposedly as far as unit size...the bosch with inverter compresor makes itself fit in homes needing a 1.5-3 ton unit. Here's a bit of info on the system. It's from an hvac forum where the members were all impressed with the technology and features.


"I can't remember who makes the cabinet, it might be Medea, but I do remember they said that it has a Mitsubishi inverter with a crazy number of real speeds to modulate from. I think they tried to get domestic manufacturers to make it, but they couldn't find anyone willing because it has too much potential to kill sales of their own modulating units.

Every other inverter driven unit I've installed is 100% proprietary compatibility only - indoor, outdoor and controls all must match or no go. The Bosch unit is compatible with anything, as long as it's a TXV coil. Single speed PSC fan - no problem. A/C only application has two wire low voltage connection, heat pump four. It doesn't communicate in any other way and it doesn't care where the fan speed is, all modulation is done based on suction temp and pressure.

The control board has minimal adjustments, the main one is what temp you want the suction to return at: 37f or 47f. It has a 3 digit trouble code reader, but you can only display the codes once and then they disappear. They said they didn't include memory because they wanted to keep the cost down of the unit, and from the preliminary number our supplier gave us, they did a good job of that.

It only comes in two sizes, 3 tons and 5 tons. The idea is that if you have a 2 ton application, just flip some dip switches and limit the capacity. What's really surprising is how cheap it is. I'm not going to start listing prices here, but when comparing it to any domestic unitary manufacturers modulating heat pumps, its no contest. I'm an American Standard dealer, and it was even cheaper than any of their two stage cooling only scroll condensers (in any size)

I'm not trying to sell these units (except maybe to my own customers) but I was just looking for someone who might have one of these systems running in the field. For all I know it may turn out to be the biggest piece of crap ever, but on paper it looks pretty freakin incredible. I bought the demo unit they had and am waiting on their coil to be delivered so I can get a matched system with an AHRI rating that will qualify for our local utility rebate. Would love to hear from anyone with more info on it."

and some more info from another site;

The Best from Bosch: Inverter-Driven Split Heat Pumps


We’re always on the lookout for exciting new products here at Able, and recently we found one that has our employees and customers alike buzzing with anticipation. We love to find products that provide excellent utility, products that fill a niche perfectly, and that’s what we have with Bosch’s new Inverter Ducted Split Air Source Heat Pump.

We all know that when it comes to comfort, nothing can match the consistency of an inverter compressor. Inverter-driven heat pumps are an ideal comfort solution in nearly any application and Bosch’s IDS system is no exception; it employs a top-of-the-line fully-modulating inverter designed by Mitsubishi.

Typically, when your thermostat makes a call for heating, it activates your furnace which then runs until your home is slightly above the desired temperature. After that, the furnace deactivates until the temperature has fallen below your desired temperature. This results in a system that keeps your home near the desired temperature rather than at it.



With an inverter-driven heat pump, you completely eliminate this short-cycling on/off cycle. The inverter can make precise adjustments to ensure that your home is being kept at the exact temperature you want. Furthermore, in addition to providing more dependable comfort, invert-driven systems also reach their target temperatures more quickly.

A vast improvement to the comfort provided is not the only benefit of an inverter-driven system, they also consume significantly less energy. This means lower energy costs, and since heat pumps are used in all seasons, those savings are year-round. These heat pumps are so efficient that they even qualify for up to $600 in rebates from ComEd!

Since Bosch’s inverter heat pump is compatible with any coil that has a TXV valve, adding it to your home is easier than most retrofits. The inverter heat pump is the perfect replacement for traditional air conditioners. Not only does it provide high-efficiency cooling, it also handles most heating applications better than a furnace.

Bosch’s IDS system also supports dual-fuel applications. This means that you can pair it with your existing furnace for the best of both worlds. The high-efficiency heat pump will handle the lion’s share of the work, keeping your home consistently comfortable even as conditions outside change. When it gets really cold, your furnace will kick in to provide additional warmth as needed.

If that’s not enough to love, there are plenty more reasons to get behind Bosch’s BOVA heat pumps. For starters, it’s quieter than the competition at only 56 dB. We’ve had several contractors install and start-up these units only to wonder if everything was running properly on account of the low operational noise level

 

[hunterdan]

and a bit more;


What is the Bosch Central Air Conditioner?
The Bosch Inverter Ducted Split Air Source Heat Pump is one of the newest, high-performance, high-efficiency heat pump systems that was introduced just last year.

Boasting of variable speed inverter drive, this innovative solution introduces precise temperature cooling and heating, enabling high energy-savings, enhanced comfort, and maximum convenience.

Available in four sizes, this groundbreaking system exhibits excellent capacity levels that range from 2-ton to 5-ton, giving you enough options whatever application you need it for.

High Energy-efficiency, Superior Performance
Bosch Inverter Ducted Split Air Source Heat Pump features an array of advanced, powerful capabilities, but if we’ll try to sum up these strengths, it would be these:

• Superior performance
• Low energy consumption
• High savings
• Maximum comfort

That’s right, this heating and cooling solution is a veritable model of high energy-efficiency and superior performance that have become the hallmark of some of the most advanced heat pump systems that are available today.

And where do these high-efficiency and superior performance come from?

Like the current crop of high-efficiency, high-performance systems, this latest comfort solution from Bosch is powered by a highly sophisticated inverter-driven compressor technology. This means that it runs using a variable speed inverter drive that adjusts the speed of the compressor, enabling the system to only use the exact energy needed. As a result, these are what you get in return:

• Precise temperature and humidity control
• Energy-efficiency
• Quick heating
• Intelligent control
• Quiet operation

Precise Temperature and Humidity Control
Designed for precise temperature and humidity control, Bosch Inverter Ducted Split Air Source Heat Pump facilitates consistent room temperature. It utilizes a variable speed system that modulates the compressor by adjusting the power output based on the heating or cooling load. This means that you’ll get the exact temperature that you need or the most precise cooling/heating load that you set.

To better understand how this works, just imagine the traditional system with a standard compressor. Let’s say you will use this system for heating. When you “turn on” the unit, the system will run at its maximum capacity until it reaches the level of temperature that you set in the thermostat. When the temperature is achieved after running at full power, the compressor stops and turns itself off. When heating or cooling load inside the room changes, the system (the compressor, specifically) runs again. Basically, this “turn-on, turn-off” cycle results to temperature fluctuation which contributes to inefficient energy-use.

In contrast, by using the variable speed technology, Bosch Inverter Ducted Split Air Source Heat Pump is able to adjust its operating speed and consume just the exact amount of energy needed to reach your desired level of temperature without any impact on the level of comfort.

Energy-efficiency, Big Money Savings, Lower Energy Bills
High energy-efficiency translates to lower electricity bills. With its highly efficient inverter drive system, Bosch Inverter Ducted Split Air Source Heat Pump is able to adjust its output level at a range between 25% and 110%, giving you more opportunity for higher money savings. Take note that this solution also boasts of 18 Seasonal Energy Efficiency Ratio (SEER) and 9.5 Heating Seasonal Performance Factor (HSPF) ratings.

Quiet Operation
With the sound level of the unit while running kept to the minimum, you would have complete peace of mind. Take note that this heat pump is a split system, which means it consists of an outdoor compressor/condenser unit and indoor air handlers.

You must understand that the noise that we often hear and associate with air conditioners and heat pump systems normally comes from the compressor. By using Bosch Inverter Ducted Split Air Source Heat Pump, you have a system where the compressor unit is placed in a suitable area outside the house. Thus, the sound of the running unit that you’ll hear from inside, if there will be any, is kept to the minimum.

Also, keep in mind that we’re not talking here about a run-of-the-mill compressor system. With this heat pump solution from Bosch, what you get is a highly advanced compressor unit that is very stable and operates with the lowest frequency and vibration. Now, add the fact that it uses the so-called silent blade and modulating comfort technologies that enable you to control the fan speeds and modulate the sound in the process.

With an average sound rating that comes as low 56 dBA, especially in its 3-ton and 4-ton units, this system is, in fact, considered as one of the quietest cooling and heating solutions today.

Quick Heating
With a frequency-adjusting compressor and exceptional air coil design, Bosch Inverter Ducted Split Air Source Heat Pump exhibits highly efficient heat transfer and dehumidification capabilities, enabling the system to quickly reach the maximum desired temperature. When needed, you will also have the option to add electric heat to the air handler.

Intelligent Control
Aided by a compatible thermostat, Bosch Inverter Ducted Split Air Source Heat Pump features intelligent control capabilities that enable the system to efficiently and effectively adjust the temperature according to your desired level of comfort.

Why Use Bosch Inverter Ducted Split Air Source Heat Pump?
While there are many similar solutions available, there’s no doubt that Bosch Inverter Ducted Split Air Source Heat Pump stands as relatively better in terms of capabilities to provide higher level comfort, temperature consistency, cost-savings, price competitiveness, control, and ultimate convenience.

For your home application, a purchase of this unit makes you eligible for a residential limited warranty, which includes an attractive 10-year protection for all original parts of the system that were incorporated during manufacture and a 1-year warranty for parts that were bought from Bosch and integrated as replacement in the field.

 

[Mac5005]

What’s the return on the investment of this type of hvac system vs conventional?

 

[shawn]

HVAC wisdom needed.

We are at the point of doing HVAC and just thought I'd see what peoples thoughts are regarding our current plan.

After doing a good bit of reading reviews and searching HVAC forums we have decided we like the Bosch system.
Home is a single above grade floor with vaulted ceiling (17') and a walkout basement with open stairway between upper floor and basement.
Bosch offers an inverter compressor heat pump in a 3 or 5 ton unit.Basically, the system does not run wide open when operating if not needed. It runs at a variable speed depending upon demand lengthening life of components and reducing energy demand. The contractor I'm planning to use plans to put the air handler/return above our closet upstairs. It will be a dual zone/split system with electric doors to upper and lower floor ductwork via upper and lower floor thermostats.
I know that every home needs calculations for "R" factors for walls,windows...but with the Bosch 3 ton unit it works with any home needing 1.5-3 ton unit. Mine needs about 2.5-3 so it will be the 3 ton.
My main concern now is that the contractor correctly figures the cubic feet per minute and such for each room or living area and the correct placement of the return.
He says he plans to install one return upstairs. It will be about 2/3 up the 17' vaulted wall dividing our living room from our bed/bath area. He also plans to install the registers for heating/cooling on that same wall....one about 8' away on each side of the return and a few feet lower on the wall.
Here's a link to a thread here on the forum which better describes the home
House build start to finish

Reason for one return is that the stairway is open to the basement

Any opinions appreciated as this system will be installed next week.

Thanks, Dan

Did you read the rest of the thread on hvac talk?

 

[hunterdan]

Did you read the rest of the thread on hvac talk?

No...what did you find.

 

[Fabrik8]

I wonder how the Bosch stacks up to something like the Bryant Evolution variable speed units that keep coming up in my research..?

 

[braxton357]

Nothing to add other than just had Perkins install a new trane system --sized correctly for the house with a variable speed air handler--so it isn't something new or even that much more expensive than conventional if all you're after is consistent cooling and humidity control.

And you may not be into it but I've been installing mult unit heat pump mini splits in rentals and people love them. They are dead silent and super efficient, not to mention you can have any room be whatever temp you want.

 

[hunterdan]

Decided to go with the Bosch Nova inverter system. They installed ductwork and air handler today. The air handler is about 170lbs and seems to be nice quality. I read a bunch of reviews and watched a number of vid's but also called a HVAC supplier in Charlotte and he said Bosch would be his next system. He also said parts have not been a problem when needed.

 

[hunterdan]

HVAC finished. Installer impressed me. I gave half down at contract signing and he showed up two hours later with materials including air handler. They started the next day and finished all interior work in a total of 2 days. He took off thanksgiving and the weekend but showed up Monday with the outside unit and installed it. Lastly he taped all the registers and did a pressure test on the ductwork. PM for his info.

 

[shawn]

Where is the insulation going to go?

 

[rockcity]

They are all required to do a leak test. The inspector will ask for it during your final so don't lose it.


I'm not sure I'd pay anyone $ up front, even people I know.

 

[hunterdan]

Where is the insulation going to go?

walls and vaulted roof.

They are all required to do a leak test. The inspector will ask for it during your final so don't lose it.


I'm not sure I'd pay anyone $ up front, even people I know.

Just depends on the job, person and amount of money for me. I also do my homework and find out where they live and check reviews/references.

 

[shawn]

vaulted roof

So, underside of roof sheathing? How are you going to prevent condensation and rot?

 

[hunterdan]

Baffles are going in the roof before the insulation. They let any interior air that makes it to the roof escape through the full length eve vents. From what I've read older houses like my 100 yr old farmhouse did not have rot issues due to good ventilation. It has no insulation either but is still a solid structure even in the attic.
Houses today are built so tight with self sealing wraps on the outside, spray insulation, sheetrock and sealer/primer paint....that they can promote condensation and rot.
Here's some good info on the topic;

Thermal Windows, Inc.

 

[shawn]

Baffles are going in the roof before the insulation. They let any interior air that makes it to the roof escape through the full length eve vents. From what I've read older houses like my 100 yr old farmhouse did not have rot issues due to good ventilation. It has no insulation either but is still a solid structure even in the attic.
Houses today are built so tight with self sealing wraps on the outside, spray insulation, sheetrock and sealer/primer paint....that they can promote condensation and rot.
Here's some good info on the topic;

Thermal Windows, Inc.

That doesn't work. Baffles are only good for about 4ft before they prevent air movement on the underside of the sheathing. If you want to do insulation in the rafters, you need to do continuous insulation on the top side of the sheathing to move the dew point outside of the wood structure. Otherwise you'll have daily wetting on the underside of the sheathing which will eventually rot the sheathing and rafters.

Alternatively, you could frame a new substructure below the rafters to support fiberglass batts and the ceiling. If I had to guess, if you do the math, it probably needs 6-8" clear vertical height under the sheathing before the insulation to get enough air movement. And then ridge and soffit vents to get some convection currents to carry away the moisture that comes from vapor drive.

 

[shawn]

Houses today are built so tight with self sealing wraps on the outside, spray insulation, sheetrock and sealer/primer paint....that they can promote condensation and rot.

Your problem has nothing to do with any of those things. It's because you have insulation and air conditioning, and you live in a mixed-humid climate zone.

 

[rockcity]

I think what Shawn is saying, you need to prevent the condensation from happening and what you have suggested won't do that and, even with baffles, you'll get condensation and eventually rot, etc.

 

[hunterdan]

Here's what I read. It says in my 24" on center rafters that a 22.5" rigid baffle from eve to ridge vent would allow air flow under sheathing. I guess their wrong or I'm just not understanding how it applies to my situation. Below is an excerpt from this pretty detailed link regarding moisture,air flow...

How Important Is Using Baffles in Attic Insulation?
Rafters
If you want to insulate the rafter bays rather than the attic floor in order to make the attic a heated space, baffles are even more important for proper air circulation. Baffles establish a channel for air to circulate between the insulation and the roof sheathing. As with attic floor insulation, moisture and heat removal are the reasons for creating proper air movement. Run baffles the entire length of the rafter bay from the soffit vent to the ridge vent, then add batting insulation over the baffles

 

[hunterdan]

here's a pic of what I mean. It does not stop at 4' like a floor insulated attic but baffles continue to the ridge vent.

 

[Mac5005]

Here's what I read. It says in my 24" on center rafters that a 22.5" rigid baffle from eve to ridge vent would allow air flow under sheathing. I guess their wrong or I'm just not understanding how it applies to my situation. Below is an excerpt from this pretty detailed link regarding moisture,air flow...

How Important Is Using Baffles in Attic Insulation?
Rafters
If you want to insulate the rafter bays rather than the attic floor in order to make the attic a heated space, baffles are even more important for proper air circulation. Baffles establish a channel for air to circulate between the insulation and the roof sheathing. As with attic floor insulation, moisture and heat removal are the reasons for creating proper air movement. Run baffles the entire length of the rafter bay from the soffit vent to the ridge vent, then add batting insulation over the baffles

Be very careful applying tech and info from a west coast news source in building your NC Home.

The dew point out there (west coast) is so different than it is here, the same building principles can’t be directly applied here, that work out there.

Increased ventilation from ambient outside humid air in our(the SE) climate will increase condensation, not reduce it.

For our climate you must design and install the correct building methods so that the material that is at or below the dew point temperature isn’t a structural wood member, ie rafter or sheathing, otherwise fungal growth (rot) will occur.

 

[Mac5005]

If you want a good read to dive into information that directly applies to our climate start here.

Info-015: Top Ten Dumb Things To Do In the South

There is plenty to study on that site, just browse around.

 

[shawn]

If you want a good read to dive into information that directly applies to our climate start here.

Info-015: Top Ten Dumb Things To Do In the South

There is plenty to study on that site, just browse around.

Lstiburek FTW. That guy knows his stuff, and it's all based on case studies and actual test data. I wouldn't consider any of the other links posted in this thread to be reputable sources of building science information.

To be fair, though. That article is focused on hot humid zones. We're a bit different. The sealed attic link in the article does explain the wetting issues, though.

 

[shawn]

View attachment 258704
here's a pic of what I mean. It does not stop at 4' like a floor insulated attic but baffles continue to the ridge vent.

I think what Shawn is saying, you need to prevent the condensation from happening and what you have suggested won't do that and, even with baffles, you'll get condensation and eventually rot, etc.

Here's a good metaphor: try sucking air through a regular drinking straw, then hook six straws together end to end and do the same. Even though the ID of the straw is unchanged, you get a lot less air through the longer straw. Same with the insulation baffles. There's only about 1-1/2" of air space behind the baffles. Their job is to make sure air gets from the soffit vents into a vented attic, and that the insulation out by the joist seat doesn't interfere with that movement. Once you hook a couple of them end to end, there isn't enough air movement in the gap to carry away the moisture laden air that's there. Condensation occurs at the dew point, water destroys wood, etc. Ten years from now, the shingles at the ridge start sagging, you pull up the roof to see what's up, and find that the sheathing and rafters are rotten.