[jcl333]

IF IT AIN'T SIMPLE, It will not work.! Is This Simple?

If you have simple solution to this, now is the time. I welcome it.

-JCL

 

[BALloyd]

I haven't read the entire thread but you likely have humidity problems because your equipment is massively oversized for new construction.

I am cooling my 2015 built 2700 square foot house with a variable speed 2 ton unit similar to that Bosch. At 100F, it doesn't run the full hour and keeps the house at 73F.

24000 btu for a modern 700 square foot basement is nuts, even in heating and you are talking about adding more. Unless of course you have no insulation

Has anyone actually done a proper load calculation.?


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[jcl333]

I haven't read the entire thread but you likely have humidity problems because your equipment is massively oversized for new construction.

It's a 3-ton unit, which can theoretically go down to 26% on the modulating/inverter compressor, that would mean it could go down to less than 1 ton.
That is assuming it can actually do that of course. I am not saying you are wrong, but I think that is what my installer was thinking.

I am cooling my 2015 built 2700 square foot house with a variable speed 2 ton unit similar to that Bosch. At 100F, it doesn't run the full hour and keeps the house at 73F.

Yeah, I wish my guy installed the 2-ton unit.

24000 btu for a modern 700 square foot basement is nuts, even in heating and you are talking about adding more. Unless of course you have no insulation

Ok, this system is not for the basement, that is separate, this is for the 2nd and 3rd floor (2 zones), totaling 1400 SF (700/floor).

Has anyone actually done a proper load calculation.?

They might have, but at the time I was not as closely involved as I am today. The guy that I got came highly recommended, so I just trusted that he knew what he was doing.

And, to be fair, we are in a bit of a heat/humidity wave here right now. Also, this was before I replaced the windows and had the ERV installed.

What would you suggest at this point? Are you saying I need to rip out this unit and put in a 2T one? That would be really expensive. If a dehumidifier can "fix" the current issue for far less money, it may even do better in the end. Even the 2T unit likely would not run under all conditions where you might sometimes want dehumidification.

You may be correct in your assessment, but I still need to figure out what I do now.

-JCL

 

[BALloyd]

Your outdoor unit should be able to be programmed to run as either a 2 ton unit or 3 ton unit.

Based on the indoor coil number, I would suspect you have a 2 to 2.5 ton indoor coil.

While the outdoor unit may modulate down low...it's not a full communicating system, so your indoor unit is likely only running at 2 different speeds, maybe 3.

Separate Dehumidification would be the way to go



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[jcl333]

Your outdoor unit should be able to be programmed to run as either a 2 ton unit or 3 ton unit.

OK, do you think it would be a good idea to do that, even if I do get a dehumidifier?

Based on the indoor coil number, I would suspect you have a 2 to 2.5 ton indoor coil.

Is that the way it is supposed to be? Is the coil I have the one meant to go with the outdoor unit from Bosch?

While the outdoor unit may modulate down low...it's not a full communicating system, so your indoor unit is likely only running at 2 different speeds, maybe 3.

I am curious about statements like this. What are these full communicating systems out there, are they better? Are they expensive?
And you say the indoor system is only running at 2-3 different speeds. As far as I know, it is just a coil with refrigerant running through it and an ECM fan blowing over it. The controller modulates the fan based on refrigerant temperature and maybe some other factors.

I guess I am just frustrated. I was told that this Bosch BOVA was one of the most advanced systems available at any price, and this was installed in 2021. I am not cheap; I told the guy I wanted the "best of the best" and I wanted it done right. I checked his references, asked for examples, everything I could. Even other HVAC guys I talked with said he was the man I wanted. And I won't say it was cheap (I know I am not allowed to mention prices on here).

I am not angry with you, just frustrated. I am not an HVAC tech, but as an IT guy who went to school for Electrical Engineering, almost all of these central heating systems are primitive to me. I realize they have to go through mass production and make a profit, but it seems to me that technology is good enough now that we could make a better HVAC system, and still be affordable. I will bet you the people on this board could design one. The only one I have been impressed with so far are these mini-splits, like my 33 SEER(!) Fujitsu's, that is impressive.

I have dealt with at least 15 different HVAC companies in the last 20 years. I have never once seen any of them ask to do a blower door test, or measure CFM out of a vent (I did see one measure the temp out of a vent), and the most recent HVAC company that installed my ERV did not even balance it. It takes 10 minutes with a differencing manometer. I would have hired them for the next 10 jobs if they treated me right (I am a landlord as well and have other properties).

Sorry for the rant. But you guys here must certainly be familair with the need to vent, right? :grin2:

Separate Dehumidification would be the way to go

OK, so sounds like we are all on the same page. Maybe not so simple, but necessary?

-JCL

 

[jcl333]

Hello all, here is an update.

I finally caught up with my HVAC guy, he is very busy. I talked with him on the phone, and I sent him the diagrams.

Here is what he had to say, although he hasn't seen the crawlspace yet, he will come out and see it:

For adjusting the Bosch BOVA to remove more humidity, he suggested the following steps:
1. First, disconnect Y2 between the zone controller and the AHU, so it will take longer to reach setpoint and remove more humidity
- I am trying this now, I disconnected Y2, and set both zones to 68F to see how low the humidity will go
- I can tell the Y2 trick is working, the air handler is much quieter, suggesting it is not going into Y2

2. He will come out, and lower the AHU fanspeed, which should help as well, also make it quieter
- He also thinks the compressor will respond automatically to the lower fan speed

3. If all of the above is not enough, he will adjust the compressor down to maybe 1.5 tons, so that it take even longer
- Even with these changes, he said it may not be enough, I may still need a dehumidifier (but it is still worth doing the above first)
- Hopefully these changes would not adversely affect heating performance in the winter season


For the other questions:
- He thinks the idea of using the crawlspace as a plenum is OK on a sprayfoam house built in 2014, but he will take a look
- He was a little concerned that we would be able to find a suitable backdraft damper for the AHU
- So, overall he is open to the idea


On the duhumidifier itself:
- He actually brought up the Santa Fe units, and said they had to stop selling them due to too many problems with them
- Main problem he said was coolant leaks
- The are so compact it is very hard to do any service on them
- He suggested the Aprilaire unit, which isn't perfect either, but reliable and easy to get parts for
- It is still very hard to work on, you sort of have to hope it doesn't break
- His main concern is how loud the dehumidifier might be when placed in the crawlspace


I think his ideas on the Bosch BOVA are good.

What do you all think?

-JCL

 

[teddy bear]

The starting point is the a/c. My understanding is that the Bosch a/c makes an effort to maintain a specific coil temperature. To max dehumidification with a/c, set the cooling coil temperature to 43^F. The compressor will increase or decrease capacity to maintain the coil temperature. The total capacity of the a/c is controlled by the indoor cooling coil air flow. A 43^F coil temperature will remove enough moisture to maintain <50^F dew point air to the home which will remove 3 lbs. of moisture per ton of cooling. The is an important start point on maintaining <50%RH in a home. During significant cooling loads, the rate of dehumidification of the a/c should be adequate to meet your needs. The key is to slow the air flow through the cooling coil to enable the compressor to maintain the 43^F coil temperature to remove max humidity. As the sensible cooling dehumidification declines and the %RH rises above 50%RH, a dehumidifier is required to remove the moisture the a/c is unable to.

With the fresh air and occupants, you will need (.5 lb per occupant and 3 lbs. per 100 cfm of fresh air) per hour from the dehumidifier and the reheat provide to the a/c to operate longer. My guess for the dehumidifier capacity would be 120-155 pints per day provided you get the a/c adjusted ideally. Your a/c will remove a couple of lbs. of additional moisture with reheat from the dehumidifier.

Regarding reliability of all dehumidifiers, all have had coil problems. The quality of copper coils have decline because recycled copper and the chemical pollutants in homes. Santa Fe has changed the material that their coils are made of and extended their coil warranty to 6 years. Fresh air change has improved the life of the cooling coils of the a/c and dehumidifiers.
Santa Fe is the most efficient dehumidifier.

Install key issues. Route the ERV and house air to dehumidifier return. The supply of the dehumidifier must be routed in the a/c supply,not the a/c return.

After install, small changes are possible to fine tune this complicated install.
It will be exciting.

Keep us posted.
Regards Teddy Bear

 

[jcl333]

Excellent reply as usual TB, this is really helpful, thank you. I will share your insights with my guy. Some replies below.

The starting point is the a/c. My understanding is that the Bosch a/c makes an effort to maintain a specific coil temperature. To max dehumidification with a/c, set the cooling coil temperature to 43^F. The compressor will increase or decrease capacity to maintain the coil temperature. The total capacity of the a/c is controlled by the indoor cooling coil air flow. A 43^F coil temperature will remove enough moisture to maintain <50^F dew point air to the home which will remove 3 lbs. of moisture per ton of cooling. The is an important start point on maintaining <50%RH in a home. During significant cooling loads, the rate of dehumidification of the a/c should be adequate to meet your needs. The key is to slow the air flow through the cooling coil to enable the compressor to maintain the 43^F coil temperature to remove max humidity. As the sensible cooling dehumidification declines and the %RH rises above 50%RH, a dehumidifier is required to remove the moisture the a/c is unable to.

3 lbs. of moisture per ton doesn't seem like allot, but I guess if it is running a lot / long enough.

Disconnecting the Y2 terminal as my HVAC guy suggested has had a small but noticeable effect, at one point humidity was down to 51%, right now it is hovering around 65%, but that is still much better than the 71%-86% I have been experiencing. Like you are saying, not enough to solve the problem but worth doing.

With the fresh air and occupants, you will need (.5 lb per occupant and 3 lbs. per 100 cfm of fresh air) per hour from the dehumidifier and the reheat provide to the a/c to operate longer. My guess for the dehumidifier capacity would be 120-155 pints per day provided you get the a/c adjusted ideally. Your a/c will remove a couple of lbs. of additional moisture with reheat from the dehumidifier.

So, you are saying .5 lbs. of humidity removal per person + 3 lbs. per 100 cfm of fresh air (depending somewhat on outdoor RH%, I imagine).
Probably should add some for evaporation from aquariums, going to add better covers to them to reduce this, one of them has this and it works well, losing maybe 5 gal / week on the uncovered one.
The upstairs are is where 4 people sleep, two full baths, laundry, and we get allot of chimney effect from the first floor.

Even so, you don't think 120-155 ppd is too much? Just seems like units rated that high are for much higher square footage than what I have.
I plan to use two dehumidifiers, the upstairs is roughly 1400 square feet in floor area, the basement/1st floor a little smaller than that.
The Aprilaire E080 is 80 ppd or 10 gal per day, which would be 3.33 pints/hour, a pint is roughly 1 pound, so 3.3 pounds per hour, yes? I realize there are way more variables than this in play.
Is the goal to try and "right size" the unit to what I need, or is it OK to oversize it a bit?

Regarding reliability of all dehumidifiers, all have had coil problems. The quality of copper coils have decline because recycled copper and the chemical pollutants in homes. Santa Fe has changed the material that their coils are made of and extended their coil warranty to 6 years. Fresh air change has improved the life of the cooling coils of the a/c and dehumidifiers.
Santa Fe is the most efficient dehumidifier.

OK, so perhaps make sure we get a recent model that has the new coil material?
The Santa Fe is a bit more efficient, 2.7/2.9 L/kWh vs 2.35 L/kWh, which is impressive if it is also using a MERV13 filter.
Would you go with Santa Fe over Aprilaire even if my HVAC guy really like the Aprilaire?

Install key issues. Route the ERV and house air to dehumidifier return. The supply of the dehumidifier must be routed in the a/c supply,not the a/c return.

Yes, when he comes out we are going to go over these issues and try and come up with a solution, maybe he will like one of my diagrams.

After install, small changes are possible to fine tune this complicated install.
It will be exciting.

It will be exciting to finally solve this.

-JCL

 

[teddy bear]

Excellent reply as usual TB, this is really helpful, thank you. I will share your insights with my guy. Some replies below.



3 lbs. of moisture per ton doesn't seem like allot, but I guess if it is running a lot / long enough.

Disconnecting the Y2 terminal as my HVAC guy suggested has had a small but noticeable effect, at one point humidity was down to 51%, right now it is hovering around 65%, but that is still much better than the 71%-86% I have been experiencing. Like you are saying, not enough to solve the problem but worth doing.



So, you are saying .5 lbs. of humidity removal per person + 3 lbs. per 100 cfm of fresh air (depending somewhat on outdoor RH%, I imagine).
Probably should add some for evaporation from aquariums, going to add better covers to them to reduce this, one of them has this and it works well, losing maybe 5 gal / week on the uncovered one.
The upstairs are is where 4 people sleep, two full baths, laundry, and we get allot of chimney effect from the first floor.

Even so, you don't think 120-155 ppd is too much? Just seems like units rated that high are for much higher square footage than what I have.
I plan to use two dehumidifiers, the upstairs is roughly 1400 square feet in floor area, the basement/1st floor a little smaller than that.
The Aprilaire E080 is 80 ppd or 10 gal per day, which would be 3.33 pints/hour, a pint is roughly 1 pound, so 3.3 pounds per hour, yes? I realize there are way more variables than this in play.
Is the goal to try and "right size" the unit to what I need, or is it OK to oversize it a bit?

The total dehumidifier capacity 120-155. Over sizing depends on you, If you are serious of maintaining <50%RH with high outdoor dew points and a breeze and do not forget the fish tanks. You will get a little help from the ERV. How about the horizontal Santa Fe Ultra 120 and Aprilaire 80. These unit are rated at 80^R, 60% and you will be at 75^F, 50%RH. Less than the rating level.

OK, so perhaps make sure we get a recent model that has the new coil material?
Ok with me, will have 6 year coil warranty and you will have fresh air which increases the coil like of any of the coils.


The Santa Fe is a bit more efficient, 2.7/2.9 L/kWh vs 2.35 L/kWh, which is impressive if it is also using a MERV13 filter.
Would you go with Santa Fe over Aprilaire even if my HVAC guy really like the Aprilaire?

After +30 years of dehu pioneering Santa Fe dehus and talking Aprilaire into the dehumidifier bussiness, I hope you go Santa Fe, but your choice.


Yes, when he comes out we are going to go over these issues and try and come up with a solution, maybe he will like one of my diagrams.



It will be exciting to finally solve this.

-JCL

You are one of the most caring and involved home owners we have had on the site. Thank you and you ready to help you a/c company sell this concept to all, expecially if the results are there.

Keep us posted of course.

Regards Teddy Bear

 

[jcl333]

The total dehumidifier capacity 120-155. Over sizing depends on you, If you are serious of maintaining <50%RH with high outdoor dew points and a breeze and do not forget the fish tanks. You will get a little help from the ERV. How about the horizontal Santa Fe Ultra 120 and Aprilaire 80. These unit are rated at 80^R, 60% and you will be at 75^F, 50%RH. Less than the rating level.

OK, I don't mind if it is oversized. I was just wondering if it might suffer the same problem as my heat pump, that it would reach the desired humidity but then because the fan is still running after that, it would re-evaporate water that is on the coil. But, maybe not an issue since it will cycle on and off until the desired humidity is reached.

Is there a dealer you could recommend where I could buy a Santa Fe dehumidifier, so that I would be sure to get the newer models with the newer coil material? I will ask my tech if he is willing to give it a try.

I have been running an experiment. I brought my stand-alone dehumidifier from the basement up to the third floor, set it to 45% and have been running it for a couple days. It struggles, but it managed to get the humidity down to 53% and still going. Not there yet, but the room is much more comfortable even at 78F.

Here is a graph of the last week for the 2nd floor.

You are one of the most caring and involved home owners we have had on the site. Thank you and you ready to help you a/c company sell this concept to all, expecially if the results are there.

Keep us posted of course.

Regards Teddy Bear

Well, I really appreciate the sentiment, thank you.

I am going on vacation for two weeks, but when I get back I am going to meet with him and go over this information and see if we can go forward, both for the upstairs and basement systems.

-JCL