Hire a mechanical engineer for heat pump?

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abqguy
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Hire a mechanical engineer for heat pump?

Post by abqguy »

[Topic is now in Personal Finance (Not Investing) - mod mkc]

Hello everybody, I'd like to upgrade the A/C in my house. I'd like to get a heat pump, to provide cooling and heating. (I'd like to eventually install solar panels too.) Currently I have evaporative cooling, also know as a 'swamp cooler', which works OK in my desert climate. I have a gas-fired furnace. My house was built in the 1950's, it's a single story, and it's about 1750 sf.

I met with an HVAC installer, and his questions lead me to believe that this is going to be a complicated installation. I am thinking, maybe I should hire a mechanical engineer to design the system? This way, I'd get consistency across all the bids I am going to receive, and each contractor would not have to 'reinvent the wheel' as far as designing a solution. I'd be sure the system was well-designed.

Has anyone else hired a mechanical engineer for something like this?

Here's why I think my situation is complicated: it seems to boil down to the ductwork:
- the existing ductwork is in a tight crawl space under the house. Right now it only connects to my gas-fired furnace. (The cooling simply blows in from an opening in the ceiling in the middle of the house.)
- the heat pump would need to be sized to account for the capacity of the ductwork, as well as the cooling/heating needs of the house.
- I'd really like to use crawl space for the ductwork, rather than putting ductwork on the roof, which would void my membrane-roof warranty
- I'd like to retain the existing furnace, and its connection to the ductwork, in case of a failure of the heat pump- though this is negotiable
- the only place to put the air handler for the heat pump is the furnace closet, so this would mean tearing out the furnace
- the exterior walls are mostly of concrete block, so it will be difficult to do penetrations
- for the new system to work well, there would have to be a provision for 'make-up air' flowing back to the air handler. There is no ductwork now for this.

The good news is there is space outside my house to put a concrete pad and the heat pump. But where to place the heat pump air handler, and how to connect it to ductwork in the crawl space, is the problem.

Does this sound like a job that warrants a mechanical engineer? Thanks for any thoughts.
hicabob
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Re: Hire a mechanical engineer for heat pump?

Post by hicabob »

You want an experienced hvac installer, not a mechanical engineer.
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NateH
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Re: Hire a mechanical engineer for heat pump?

Post by NateH »

I have a degree in mechanical engineering and I would take your money and hire an HVAC person to re-duct your house to get the cooling flow high enough for the heat pump specs, then take the rest of the month off while HVAC person does everything.
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chinchin
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Re: Hire a mechanical engineer for heat pump?

Post by chinchin »

If anything you would want a civil engineer.

But I would go with HVAC tech.
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iamlucky13
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Re: Hire a mechanical engineer for heat pump?

Post by iamlucky13 »

I'm also a mechanical engineer. This is a very broad field, and most of us have nothing to do with HVAC. Even the mechanical engineers who design the HVAC components like pumps, condensors, valves, etc, I suspect don't have expertise in designing installations. Maybe someone with more direct experience relevant to your situation will chime in, but just in case, I'll give my 2 cents:

There is a specialization within mechanical engineering for HVAC engineering, which is primarily focused on complex commercial or industrial systems. A friend of mine went this route and as of when I last talked to him, mostly works on very large, complex factory systems, both for HVAC and for process temperature control. A home should not need an HVAC engineer's expertise. Even with complex installation challenges, the same considerations should still apply for system sizing and selection.

I believe there are also HVAC system designers who can either work with the engineers to help with the specifying components and determining layouts for large commercial and industrial projects but generally stay away from the detailed calculations, or can work with installers or construction firms to design systems for smaller commercial buildings with an intermediate level of complexity.

I would think this latter category could help with a complex residential system design, but I don't know how you go about getting engaged with an HVAC designer who works on a consulting basis.

While working with a designer to arrive at a specific design that you could have different installers to quote could help with consistency between quotes, I do not think this would end up being the most cost-effective solution. I would still lean toward working with an HVAC installer, but one with experience retrofitting older homes, and if they identify parts of the project they can't perform themselves, like large penetrations in load-bearing walls, get clear details from them about what else needs to be done, and bring in another contractor to do that work.
Jeepguy
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Re: Hire a mechanical engineer for heat pump?

Post by Jeepguy »

hicabob wrote: Tue Jul 09, 2024 5:33 pm You want an experienced hvac installer, not a mechanical engineer.
+1
gutterman
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Re: Hire a mechanical engineer for heat pump?

Post by gutterman »

My son is in college studying to be a mechanical engineer. He did a cooperative education program for a semester where he worked for an engineering firm designing HVAC systems. He told me he learned quickly he wanted to find a job where he did not sit in front of a PC all day doing CAD.
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Re: Hire a mechanical engineer for heat pump?

Post by Jack FFR1846 »

I have a friend who does HVAC designs. These are only for commercial buildings as systems for houses are so well known and small that a "design" per se isn't needed. Running X amount of ducting per linear foot of Y size for heat/cooling and Z amount of ducting for returns of R size are standard and well known.

Of concern: You have no return ducts. Regardless of your heating system type, you need returns. Otherwise your heating system will not work correctly. For a system without ducts, how does the air get back into the system? Inside the house, you'd literally have drafts. Outside the house, this would be an extremely inefficient system.

A good HVAC contractor is who you want doing this system. They'll figure things out and can also give you alternatives. I have a wood furnace and oil furnace in my house and the interface is quite simple and fail proof. I'm sure they'd figure out something similar for your system.
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NYCaviator
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Re: Hire a mechanical engineer for heat pump?

Post by NYCaviator »

abqguy wrote: Tue Jul 09, 2024 5:22 pm
- I'd really like to use crawl space for the ductwork, rather than putting ductwork on the roof, which would void my membrane-roof warranty
- I'd like to retain the existing furnace, and its connection to the ductwork, in case of a failure of the heat pump- though this is negotiable
- the only place to put the air handler for the heat pump is the furnace closet, so this would mean tearing out the furnace
- the exterior walls are mostly of concrete block, so it will be difficult to do penetrations
- for the new system to work well, there would have to be a provision for 'make-up air' flowing back to the air handler. There is no ductwork now for this.
.
Sounds like you'd be an excellent candidate for a mini-split system. I wouldn't be too concerned about drilling into the walls; it can be done, especially if you already have a crawl space. Do you have an attic?

The problem you run into with trying to retrofit new ductwork in a very old house is that it can be a major project and very expensive (if even possible). When you say "make-up air" do you mean a return duct?

Having just had a heat pump system installed, the air handlers are bigger than a traditional furnace and A/C. Ours barely fit. Are you sure it'll fit in the closet your furnace is currently in, with enough room to spare? (especially if you don't already have an A/C condenser)

I'd look at a mini split system and keep the furnace as a backup if you want (though it's not necessary with the new systems unless your desert climate gets VERY cold). It'll be more efficient and likely cheaper to install. If my house didn't already have central air, I'd definitely go 100% mini split. They are pretty awesome and you don't have to run the system in parts of the house you aren't using.
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Re: Hire a mechanical engineer for heat pump?

Post by Dude2 »

Isn't it a thing nowadays that if you have issues with ducting, you go the "mini-split" route. Instead of having one central unit that pipes the air to each room (and associated returns), you end up with a unit in each room (or placed into key rooms). They install it on the wall up high, and there is an associated outdoor unit for each one. It is widely used outside the US and claimed to be more efficient. One problem is for people with HOAs, it can be difficult to get approval to install those outdoor units on the opposite sides of the walls, tending to have rules in place that force you to put your main outdoor AC unit in the back of the house.
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abqguy
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Re: Hire a mechanical engineer for heat pump?

Post by abqguy »

My thanks to everyone who has weighed in so far. I was not considering mini-splits, due to concerns about esthetics, and the difficulty of drilling through concrete block walls.

But it seems like the crucial factor is the difficulty of providing for return air ducts. My house has a flat roof, so no attic and no ability to run return air ductwork up there. I'm not part of an HOA, so there aren't constraints about where to locate compressors etc.

So I guess I need to get educated about mini-split systems, and how to minimize the appearance problems. My house has simple stucco'd walls, and having tubing running across them is not appealing.
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firebirdparts
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Re: Hire a mechanical engineer for heat pump?

Post by firebirdparts »

The normal way has always been to insert the heat pump indoor coil in the ductwork downstream of the furnace. You wouldn't buy an air handler, just a box with a coil in it. They make a brain to cut the heat pump off when the furnace comes on. The furnace functions as "stage 2" but it takes out the heat pump when it comes on. The furnace fan gets told to turn on during A/C.

Sounds "involved" on the control side, but that's a very normal installation. Should be common knowledge.

There could certainly be reasons why you can't fit the indoor coil where you want to, but they'd have to be pretty strange. I suppose, depending on the climate, there could be a situation where the furnace is "really tiny" and its fan and ductwork are too small for your desired huge a/c. We don't have that kind of info in this thread.

You can certainly take the furnace out if you want to, but you didn't seem to go there.
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zeeke42
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Re: Hire a mechanical engineer for heat pump?

Post by zeeke42 »

Dude2 wrote: Wed Jul 10, 2024 7:31 am Isn't it a thing nowadays that if you have issues with ducting, you go the "mini-split" route. Instead of having one central unit that pipes the air to each room (and associated returns), you end up with a unit in each room (or placed into key rooms). They install it on the wall up high, and there is an associated outdoor unit for each one. It is widely used outside the US and claimed to be more efficient. One problem is for people with HOAs, it can be difficult to get approval to install those outdoor units on the opposite sides of the walls, tending to have rules in place that force you to put your main outdoor AC unit in the back of the house.
The multi-split units that can run 3-5 indoor units per outdoor are more common in whole-house retrofit projects. They're not as efficient as the 1:1 mini splits because the outdoor units can't ramp down as far, but they're still quite good. We have two systems, each consisting of an outdoor unit, a 'branch box' in the basement, and 4 indoor wall units. 8 separate outdoor units would be insane.
rogue_economist
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Re: Hire a mechanical engineer for heat pump?

Post by rogue_economist »

Not sure a mechanical engineer is the right person, but you probably don't want HVAC installer. They don't have the background to design anything they just nail and screw things in place that other smarter people designed.

I'd look for an HVAC engineer to get it done right.
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abqguy
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Re: Hire a mechanical engineer for heat pump?

Post by abqguy »

Again, thank you everyone for your comments.
firebirdparts wrote: Wed Jul 10, 2024 10:32 am The normal way has always been to insert the heat pump indoor coil in the ductwork downstream of the furnace. You wouldn't buy an air handler, just a box with a coil in it. They make a brain to cut the heat pump off when the furnace comes on. The furnace functions as "stage 2" but it takes out the heat pump when it comes on. The furnace fan gets told to turn on during A/C.
This would not be possible with my furnace. The furnace blows down into a plenum, which is located in the crawl space. The plenum then branches out into the various ductwork. Installing the heat pump in the crawl space would be really difficult, as would be any future maintenance.

But it is interesting to know that this is how a typical install might work.
talzara
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Re: Hire a mechanical engineer for heat pump?

Post by talzara »

abqguy wrote: Tue Jul 09, 2024 5:22 pm Does this sound like a job that warrants a mechanical engineer? Thanks for any thoughts.
iamlucky13 wrote: Tue Jul 09, 2024 10:59 pm I would think this latter category could help with a complex residential system design, but I don't know how you go about getting engaged with an HVAC designer who works on a consulting basis.
rogue_economist wrote: Wed Jul 10, 2024 11:18 am Not sure a mechanical engineer is the right person, but you probably don't want HVAC installer. They don't have the background to design anything they just nail and screw things in place that other smarter people designed.
Green building contractors sometimes contract out the HVAC design separately. They use the HVAC contractor only for the installation, not the design. That's because they build houses so efficient that HVAC contractors can't believe it.

If you can find one in New Mexico that builds single-family houses, they may be willing to refer you to the person they use to do HVAC designs.
talzara
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Re: Hire a mechanical engineer for heat pump?

Post by talzara »

abqguy wrote: Wed Jul 10, 2024 3:28 pm This would not be possible with my furnace. The furnace blows down into a plenum, which is located in the crawl space. The plenum then branches out into the various ductwork. Installing the heat pump in the crawl space would be really difficult, as would be any future maintenance.
It sounds like you have a single return system. Your utility closet is the return. Does it have louvers on the door to let the air in?

If you remove the furnace, you should be able to install a heat pump air handler where the furnace is. You don't have to change anything else. You don't have to add return ducts. You can keep it as a single return system. You just have to be willing to remove the furnace.

Albuquerque has a heating-dominated climate. Because the city is a mile high, it's about as cold in winter as Richmond, Virginia. It would be best to install a low-temperature heat pump that can work in that climate. A ducted mini-split will probably be the best choice.
Agg97
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Re: Hire a mechanical engineer for heat pump?

Post by Agg97 »

abqguy wrote: Tue Jul 09, 2024 5:22 pm [Topic is now in Personal Finance (Not Investing) - mod mkc]

Hello everybody, I'd like to upgrade the A/C in my house. I'd like to get a heat pump, to provide cooling and heating. (I'd like to eventually install solar panels too.) Currently I have evaporative cooling, also know as a 'swamp cooler', which works OK in my desert climate. I have a gas-fired furnace. My house was built in the 1950's, it's a single story, and it's about 1750 sf.

I met with an HVAC installer, and his questions lead me to believe that this is going to be a complicated installation. I am thinking, maybe I should hire a mechanical engineer to design the system? This way, I'd get consistency across all the bids I am going to receive, and each contractor would not have to 'reinvent the wheel' as far as designing a solution. I'd be sure the system was well-designed.

Has anyone else hired a mechanical engineer for something like this?

Here's why I think my situation is complicated: it seems to boil down to the ductwork:
- the existing ductwork is in a tight crawl space under the house. Right now it only connects to my gas-fired furnace. (The cooling simply blows in from an opening in the ceiling in the middle of the house.)
- the heat pump would need to be sized to account for the capacity of the ductwork, as well as the cooling/heating needs of the house.
- I'd really like to use crawl space for the ductwork, rather than putting ductwork on the roof, which would void my membrane-roof warranty
- I'd like to retain the existing furnace, and its connection to the ductwork, in case of a failure of the heat pump- though this is negotiable
- the only place to put the air handler for the heat pump is the furnace closet, so this would mean tearing out the furnace
- the exterior walls are mostly of concrete block, so it will be difficult to do penetrations
- for the new system to work well, there would have to be a provision for 'make-up air' flowing back to the air handler. There is no ductwork now for this.

The good news is there is space outside my house to put a concrete pad and the heat pump. But where to place the heat pump air handler, and how to connect it to ductwork in the crawl space, is the problem.

Does this sound like a job that warrants a mechanical engineer? Thanks for any thoughts.
I’m a mechanical engineer with an HVAC specialty, mostly commercial-side. Sounds like you’re in a desert environment Arizona, NM, Utah, etc. My suggestion would be to find an HVAC company that does both residential and small commercial work. They will have the people who can assist with designing and installing your system.

Lots of different options these days for heat pumps…traditional heat pumps, mini-splits, VRF, etc. My general rule is to find somebody honest first-and-foremost, and then figure out if they’re competent to help with your design/installation. Also, pay attention to refrigerants. R-410a is getting phased out and the alternatives, while “better” for the environment have other issues such as being flammable/combustible.

HVAC is very location-dependent when it comes to the install side. The theory / engineering side is more generic with “climate zones”. You want local knowledge.

Agg97
TheDDC
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Re: Hire a mechanical engineer for heat pump?

Post by TheDDC »

Dude2 wrote: Wed Jul 10, 2024 7:31 am Isn't it a thing nowadays that if you have issues with ducting, you go the "mini-split" route. Instead of having one central unit that pipes the air to each room (and associated returns), you end up with a unit in each room (or placed into key rooms). They install it on the wall up high, and there is an associated outdoor unit for each one. It is widely used outside the US and claimed to be more efficient. One problem is for people with HOAs, it can be difficult to get approval to install those outdoor units on the opposite sides of the walls, tending to have rules in place that force you to put your main outdoor AC unit in the back of the house.
Yeah... Hard no. They look like crap and require more holes to be made in the outside of the house. No thanks.

-TheDDC
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Dude2
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Re: Hire a mechanical engineer for heat pump?

Post by Dude2 »

TheDDC wrote: Wed Jul 10, 2024 7:27 pm
Dude2 wrote: Wed Jul 10, 2024 7:31 am Isn't it a thing nowadays that if you have issues with ducting, you go the "mini-split" route. Instead of having one central unit that pipes the air to each room (and associated returns), you end up with a unit in each room (or placed into key rooms). They install it on the wall up high, and there is an associated outdoor unit for each one. It is widely used outside the US and claimed to be more efficient. One problem is for people with HOAs, it can be difficult to get approval to install those outdoor units on the opposite sides of the walls, tending to have rules in place that force you to put your main outdoor AC unit in the back of the house.
Yeah... Hard no. They look like crap and require more holes to be made in the outside of the house. No thanks.

-TheDDC
My last house had central air, returns in bedrooms -- nevertheless, one side of the house just did not get cool like the other side. It was just a flawed design. Whoever did the math didn't do it right in terms of airflow or size of unit. It's the classic problem. For one side of the house to be livable, you have to freeze out the other side.

In this case, I thought it would have been a decent approach to add a single mini-split in one of the bedrooms on the hot side. Of course they always tell you not to do stuff like that as the main A/C will fight with the other one and lead to inefficiencies. Another simple approach would be to add a window A/C unit, and just use it when it seemed too hot in that section of the house.

Anyway, bottom line was HOA would have said no to either of those approaches. "Looks ugly." Somebody should be working to address that issue.
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audioengr
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Re: Hire a mechanical engineer for heat pump?

Post by audioengr »

Perhaps you could use the floor mounted version of the mini-split system. Maybe the piping can be brought up through the crawl space.

https://www.mitsubishicomfort.com/resid ... lID=MFZ-KJ
inverter
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Re: Hire a mechanical engineer for heat pump?

Post by inverter »

I hired a mechanical engineer for a renovation of my parent's house in Atlanta. There are three primary "things" they will make as deliverables: Manual J, Manual D, Manual S.

A Manual J is a load calculation for your house. I would highly recommend that you do this, as it will give you common "sizing" across all of the vendors that give you a quote. Note that this is a pure "garbage in, garbage out" exercise. If you don't have the details of your building envelope -- insulation, window and door quality, etc. -- the report will be an estimate.

Manual D is duct design. This will only be helpful if you are willing to rip out all of your ducting and start over. You'll need detail pictures, or better yet architectural drawings for your home.

Manual S is detailed equipment selection. This will only be helpful if you know which brand/manufacturer you want to go with.

We did all three to the tune of about $4000 for our gut remodel. If you're just doing Manual J, which I would recommend, you can probably get it for about $500, but you'll need to do some serious homework on your home.

Reputable vendors include Positive Energy, HVAC Design Pros, Energy Vanguard.
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Re: Hire a mechanical engineer for heat pump?

Post by dbr »

I have an older home with hot water radiators (they are wonderful, by the way). We have recently installed mini-splits for air conditioning and cross over season heating. This has become very popular in our area where it is the obvious solution to getting air conditioning in houses that don't have hot air heat. There is the benefit of tying into modern heat pump technology, some of which is even usable for heating down to 0F.

Retro installation is not the neatest thing. Generally they run conduit for working fluid and electrical cabling on the outside of the house, and each unit needs an exterior drain hose. It is conventional to cross the house by installing conduit through the basement rather than around the house.

I would say the mini-split is an excellent solution for some homes. A benefit is being able to control independent zones. We run our bedroom by itself quite cool at night by turning on the one box there and not cooling anything else. The minisplit is a good solution to cooling an upstairs room that might get quite hot under the roof.

If a person want some sort of unified control of multiple spits, possibly multiple heat pumps, and then also a conventional heating system, possibly automated under one master control that might not exist yet for the home. A systems engineer would be required for that. I think for our needs the HVAC company did an excellent job of assessing a good design, sizing everything correctly, and then executing a not simple installation effectively and professionally.
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abqguy
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Re: Hire a mechanical engineer for heat pump?

Post by abqguy »

audioengr wrote: Thu Jul 11, 2024 8:19 am Perhaps you could use the floor mounted version of the mini-split system. Maybe the piping can be brought up through the crawl space.

https://www.mitsubishicomfort.com/resid ... lID=MFZ-KJ
This is a really interesting idea. It might just work. Thanks for sending this along.
dbr
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Re: Hire a mechanical engineer for heat pump?

Post by dbr »

abqguy wrote: Thu Jul 11, 2024 11:37 am
audioengr wrote: Thu Jul 11, 2024 8:19 am Perhaps you could use the floor mounted version of the mini-split system. Maybe the piping can be brought up through the crawl space.

https://www.mitsubishicomfort.com/resid ... lID=MFZ-KJ
This is a really interesting idea. It might just work. Thanks for sending this along.
I have the that floor mount unit in one room. It works fine. Note that the inputs to the unit are on the back and come through the wall of the house from the outside. The heat pump itself sits on the ground outside that location. You could in theory construct a cabinet behind the unit and bring inputs up through the floor. Don't forget minisplit units also need a drain tube going somewhere, usually just to ground outside.

There is a house on my block that actually has a heat pump set on flat roof area over the second story and then feeds inputs to rooms on the third floor and down to the second floor.
Saving$
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Re: Hire a mechanical engineer for heat pump?

Post by Saving$ »

Your instincts are correct. There are firms who specialize in designing residential HVAC systems, and you can get a design for a system far superior to what most HVAC techs will "design." Energy Vanguard is one of them. I have no affiliation with them other than being a happy customer.

Your challenge will be in:
a. Getting HVAC firms to bid on the exact design. There will be things in the design & specs that may differ from what the proposers are familiar with, and many firms don't want do anything that differs from their SOP, so they will either not propose or just ignore those things and propose on whatever scope they want
b. Ensuring that whomever you hire actually installs to the designed specs. Typically the way this is done is a combination of an owner who understands the intracacies of what was designed so they can supervise the install and watch for quality and then hiring a third party commissioning agent to supervise the some aspects of the install (charging the system, etc.) and conduct tests to ensure the system meets the requirements (cfm at each supply, static pressure, duct leakage, etc.)

Depending on your market, you may have trouble finding an HVAC installer willing to install on a job at which there will be a third party commissioning agent. However, if you find a commissioning agent, they may have recommendations on which installers do a great job. The trouble is you want to make sure there is some distance between the two firms. All of this costs money, and it is difficult to recoup on a residential system.

Your best bet might be to do some research on high performance contractors, or passive home builders in your area, contact them and ask who they use for their HVAC system.
Jeepguy
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Re: Hire a mechanical engineer for heat pump?

Post by Jeepguy »

If it were my home I would install a heat pump air handler where the furnace is, like talzara suggested.
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Re: Hire a mechanical engineer for heat pump?

Post by snackdog »

We finally fixed our myriad HVAC problems by moving to a different house with proper design, insulation, new windows, and great equipment. It is night and day. The whole house stays 68-75F year round.
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dbr
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Re: Hire a mechanical engineer for heat pump?

Post by dbr »

snackdog wrote: Fri Jul 12, 2024 3:42 am We finally fixed our myriad HVAC problems by moving to a different house with proper design, insulation, new windows, and great equipment. It is night and day. The whole house stays 68-75F year round.
When we bought the old house we live in we ran an energy audit for suggestions for what might be done to improve energy efficiency. The overall conclusion of the audit is that for the area in which I live to have energy efficient housing it would be necessary to simply raze the entire city and start over with "proper design, . . . "

Otherwise you make do with what it is.

Your observation is essentially correct.
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