VarSpd 14seer a waste for my basement?

[shorton]

Hi guys:

I need some professional input. I've shopped around having my basement unit installed, and I've received wildly varying opinions. I'm a Mechanical Engineer and have a decent handle on the technicalities, several times it has been more than the estimators. But I got some input that made me uncertain of my choices.

My basement and home is tight. Real tight. I won't bore you with the details, but suffice it to say it is dry enough to lay hardwood. It's a walk out basement, rear wall only now below grade. HVAC calc gave conservative numbers for very low load (<1 ton IIRC). I have ~1700 ft2 and will have about 9 ducts to the floor plan.

It will be a split unit. Lines were installed when the house was new, ready to add the basement unit later.

The house has radon and a radon mitigation system. I'd like to add an ERV to supplement that system for peace of mind.

That's the parameters.

The least experienced techs want to put in a 2 ton unit becasue they say they need the airflow. I think 2 tons will be too much and the unit will satisfy too quickly leading to poor comfort.

I figure the 1.5 ton will be better as I already don't have squat for a cooling load, and as the basement is insulated to the max and in a fairly mild climate (Tennessee) I don't have much heat load, either. I figure it would be better to have less flow at each duct and have them run longer than to have an oversized unit.

On the other end of experience, a former factory rep wants to put in a 1.5ton variable speed 15/14 seer unit. Says I need the variable speed becasue of the basement.

What unit is going to give me the best comfort levels, and efficiency in this well insulated, tight, waterproof basement?

Thanks!

[BaldLoonie]

York makes a 1 ton unit. You want a unit to run & run down there to keep the humidity down! Even then you might one of Teddy Bear's dehums, and they make a model that lets you bring in outside air too.

[BaldLoonie]

York makes a 1 ton unit. You want a unit to run & run down there to keep the humidity down! Even then you might one of Teddy Bear's dehums, and they make a model that lets you bring in outside air too.

[shorton]

What about the low CFM of a one ton unit? That's the reason the others were insisting I needed a 2 ton.

Is "teddy bear" a brand or a user here? Can you point me to a site where I can see what they have?

[Random Guy]

Less than a ton for the just the basement, or for the whole house?

You might want to look at mini splits.

[beenthere]

The amount of air flow required is not determined by the number of supplies you plan.

If your basement only needs 1 ton. Then douobtful you need more then 400 CFM.

How many rooms are you going to have in this basement.

[bob_scheel]

Hi guys:


The house has radon and a radon mitigation system. I'd like to add an ERV to supplement that system for peace of mind.

On the other end of experience, a former factory rep wants to put in a 1.5ton variable speed 15/14 seer unit. Says I need the variable speed becasue of the basement.

What unit is going to give me the best comfort levels, and efficiency in this well insulated, tight, waterproof basement?

Thanks!

Does the load calc include the ERV infiltration? I would go w the 1.5 ton variable because of the ERV and also because w a walkout its likely that you will have outdoor parties that move indoors at times. And adding some xtra bodies will push up your load numbers. Not to mention going back and forth thru the door while BBQ'ing etc.

[beachtech]

teddy bear = thermastor.com :)


its funny where the name for the santa fe line came from :D ssshhhh i am not tellin :p

[shorton]

Does the load calc include the ERV infiltration? I would go w the 1.5 ton variable because of the ERV and also because w a walkout its likely that you will have outdoor parties that move indoors at times. And adding some xtra bodies will push up your load numbers. Not to mention going back and forth thru the door while BBQ'ing etc.

Thanks guys. Looks like you need more information to help. Here is some more, please ask if I there is anything else.

Bob: There will be little to zero in and out via the basement rear doors. We have a side porch and a upstairs rear deck that gets that activity and is where the grill is. We never use the basement exterior doors, unless we are moving something into or out of the room. There is a normal exterior type door that leads to a buffered non conditioned room, then another door to the downstairs garage. Any in-out activity is throught those 2 sets of doors. Very little infiltration. The house is built tight. Very tight. Tyvek wrapped with sealed nail heads and taped seams. All windows sealed with expanding foam, etc. What happens when an engineer oversees it. Too tight :).

The main room is to be a large home theater room, but it only has 4 seats. We are not the entertaining type, we rarely have more than 2 people in the basement at any time. We have 2 kids they may have some friends over, but this is an exception, not the rule.

There is an office that has PC's etc. so a little extra heat from those maybe.

I was pretty careful on entering the data for the loads, I used a trial version of HVAC-Calc that has about expired. And, I can't change from the default outside temp values which are extreme. It reported:
SG=8089 BTUH
LG=2274
HG=10363
Total Heat Loss=24269

Here is a copy of it in pdf:
http://www.companypostoffice.com/scott/hvac1.pdf

I accepted the recommended infiltration in the program. I did not add any forced.

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beenthere: The basement will have 1BR, 1 office, 1 home theater room (16x32), 1 playroom, 1 full bath, 1 workroom.

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beachtech: Thanks, Id' have never guesed that one :)

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Baldloonie: For what it is worth, the basement is unusually dry. It has 6" of washed gravel under the slab, Certainteed's form-a-drain footer vent system, 4 feet of washed gravel topped with geotextile on the subgrade sides. Slab is cut and cuts, corners, all cracks sealed with urethane caulk. The 600cfm radon fan pulls about 1/4" of pressure under the entire slab 24x7. It woudl do better except for the external drainage "communicates" air into the system. No gutters drain onto the ground (all are piped). Due to the extensive drainage, I almost have trouble keeping my bushes alive due to the dry soil. Plus it's a poured concrete basement, 3/8" of RubberWall (long story on why it is so thick) on the outside along with a few inches of styrofoam on top of that. I even have a bead of bentonite between the wall pour and the footer.

So this is not the average basement. Any humidity is coming from internal sources and ambient air. Not from the fact it's a basement per se. I understand the cool conditions and ambient humidity are not to be discounted, but wanted to point out the construction makes it quite dry. Dust remains dry under a piece of 4 mil plastic laid on the slab floor.

This system is just for the basement. I have a separate unit for upstairs.

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Just based on equipment and contractor availability, if a 1.5 ton will work, it would be my preference. But I want to get it right the first time.

Thanks very much to all for the time to assist.

[beenthere]

What I don't see on it, is an allowance for heat gain from the entertainment/home theater equipment.

Do you know its rating.

If it puts you over 9,000 sensible, the York 1 ton will fall short.
In which case, you would need to go to a 1.5 ton.

[bkcalhoun]

Where do you live? What are the design conditions for your area? Probably not 105* and 100 grains !!!! We don't see that in Pittsburgh,PA. That will change your heat gain considerably. Variable speed should not change how much airflow you get from your system. 400 cfm/ton is 400 cfm/ton no matter what fan blows it. If you need more air movement then use some fans. Size the unit according to the heat gain.

Lets assume your calculated value of 10kbtu cooling is correct for now. If you get a 1 1/2 ton unit you are already 50% oversized. This will more than allow for extra loads from the full bath, people, entertainment system and ERV.

2 ton is a mistake in my opinion.

[shorton]

beenthere:

I do not know the values for the AV components. They will only run a few hours at a time, but one of them is a projector. I belive it has a 250w UHP bulb. Otherwise, I don't know it's heat output. If you can give me an idea on how to determine them I will look them all up.

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bkcalhoun:

The home is in the Nashville, TN area

I don't understand what you mean by "Variable speed should not change how much airflow you get..". If the fan is on low speed, it won't be producing as many CFM as when it is on high speed. So can you elaborate so I understand what you mean?

I only have the demo version of hvac-calc. It won't let you change the outside temps or grains. If it would help, I can pay for the homeowner version. But it appeared I will be on the low side, even with the elevated (and lowered) outside temps, so I didn't buy the homeowner version.

[shorton]

Hi guys:

My HVAC-calc demo program is very old so I downloaded it again a few minutes ago. The new version appears to allow the changing of the temps to my area. I will rerun the data and produce a more accurate report, and post here asap.

Thanks, Scott

[bkcalhoun]

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I don't understand what you mean by "Variable speed should not change how much airflow you get..". If the fan is on low speed, it won't be producing as many CFM as when it is on high speed. So can you elaborate so I understand what you mean?


Variable speed is designed to give 400 cfm/ton or 350cfm/ton or 450 cfm ton depending upon what you set it to do over varying air pressures. It gives a softer startup and a slower shutdown and lower electrical usage overall in a properly designed duct system. It will also allow you to operate the unit on fan setting with the blower operating at a very low speed. Variable speed units are typially rated for total esp of .8" where conventional units are rated for .5" total esp. When variable speed units are subjected to high static pressures they adjust the fan speed to compensate. Whether it is a regular unit or a variable, basic refrigeration tells us that 400 cfm/ton is required. The startup and post shutdown airflows may be different, but during steady state operation, 400 cfm/ton is required. The exception to that relu is 350/ton for dehumidification. In order to match indoor and outdoor units, sometimes a variable speed air handler is required to achieve the rated SEER of the outdoor unit.

[shorton]

Nope, I was wrong. Can't use the new demo, it does not show the results, which is understandable of course. Happy to buy it if it will help you guys help me. But I don't want to if it's not necessary.

Thanks.

[shorton]

Variable speed is designed to give 400 cfm/ton or 350cfm/ton or 450 cfm ton depending upon what you set it to do over varying air pressures. It gives a softer startup and a slower shutdown and lower electrical usage overall in a properly designed duct system. It will also allow you to operate the unit on fan setting with the blower operating at a very low speed. Variable speed units are typially rated for total esp of .8" where conventional units are rated for .5" total esp. When variable speed units are subjected to high static pressures they adjust the fan speed to compensate. Whether it is a regular unit or a variable, basic refrigeration tells us that 400 cfm/ton is required. The startup and post shutdown airflows may be different, but during steady state operation, 400 cfm/ton is required. The exception to that relu is 350/ton for dehumidification. In order to match indoor and outdoor units, sometimes a variable speed air handler is required to achieve the rated SEER of the outdoor unit.

Thank you for the explanation. I believe I had a fundamental misunderstanding of what variable meant. That helps. So is the refrigeration system effectively off when the varible speed part shifts into continous very low speed? Since it doesn't have the right airflow? I'm a little fuzzy there still.

With a 1.5 ton unit, and the respective 600cfm of flow needed per your description above: If I have 9 equal ducts, they would get 66cfm each. This is where the "2 ton" recommending people start saying that isn't enough airflow. It seems obvious to me that I do not need 2 tons, but I don't have the experience or skill to argue about the effects (or lack of effect) of the low airflow at each duct. Or perhaps it is the air veloicity they are concerned with. In any case, can you guys spread any light on how this would work in a simple, perfect system with 1.5 ton unit and 9 or 10 ducts?

I can find someone to do what I request for the work, but I can't seem to find anyone with the solid understanding I prefer. So far, almost everyone is doing it by "rule of thumb" and a ductalator. Which apparently tells them to use a 2 ton unit :(

[gary_g]

So is the refrigeration system effectively off when the varible speed part shifts into continous very low speed?(

Yes, that would be when you select fan "on" instead of "auto" at the thermostat.

Fan is the air handler variable speed fan.

Fan "on" circulates air in the house (at low flows with a v-s motor) without the air conditioning system running. If you had a non-vs motor, the fan would run at its normal speed, not at a reduced cfm.

Some thermostats (Honeywell VisionPro w/De-humidification) can slow the variable speed fan down while running the a/c cycle to lower the humidity in the house. This is different from running fan "on".

Take care.

[shorton]

What I don't see on it, is an allowance for heat gain from the entertainment/home theater equipment.

Do you know its rating.
I found the forumulas to calculate the loads from the AV equipment. I will get to work on the details.
http://www.engineeringtoolbox.com/indoor-temperature-humidity-d_114.html

[shorton]

Gary, thanks. That helps. I beleive I understand now.

So I'm back to the original main problem of whether or not a 1.5 ton unit will work and whether or not to use variable speed.

From your explanation it appears the main advantage of a variable speed unit is I could a) run it continously to keep the air circulating, and b) if I get a thermostat like the one you mentioned, take advantage of some dehimidification abilities of the slower that normal (i.e. 350cfm) fan of the variable speed unit. Right?

I will calculate the loads of the AV equipment. But I don't expect them to be that high. Particularly with low usage.

I do have an adjoining 600ft2 room I had not planned to condition. I use it occasionally (workshop type room), and had considered adding to electric dampers (on for in one for return). But this room is not used often. It is below grade and stays fairly comfortable without any help. I will see about adding it to the loads, too to see where that puts me. My main concern is how the basement will be comfort wise when the extra loads are not there. And to get my contractor to build it right the first time.

[shorton]

If I choose to use the ERV, how do I account for that additional load in hvac-calc? There is a box for forced ventilation, but I figure that is for non-ERV type ventilation.

Any rules of thumb for this load? Perhaps it iwll put me more cleanly into the 1.5 ton range.

Thanks again for all the input.

[ga-hvac-tech]

I used to finish basements before I moved to HVAC only. What caused me to learn HVAC was the same issue the OP has: Nobody seemed to understand how to size a unit for a basement. I had to learn the trade to do my basements...

There are a few questions I would like to ask:

1) There was mention of computer(s); how many boxes, how many monitors, how many UPS power supplies, etc? My office has a lot of electronic equipment, I had to add an extra 6" duct to keep it comfortable in the summer.

2) The person that mentioned the home theater and how much heat the equipment will produce has a point IMO. My home theater produces quite a lot of heat... not enough to cause a serious problem, but it is clear that it produces lots of heat.

Could you post the number of windows and doors, and rough sizes? THX.

IMO the one ton York would be too small... With 1700 SQ/FT, the 1.5 ton might just barely do... but if the added heat load of lots of computer equipment and a home theater, along with half a dozen warm bodies (maybe more, one never knows about these things)... the added capacity might be worth looking into.

The ERV unit will add outside air, so that air will need to be heated or cooled (possibly de-humidified) also.

And who knows if you might end up with an 'in law' living in the basement 'apartment' sometime down the road... :)

If it were me, I would definitely go with the VS (variable speed) blower, and work some more on the 1.5 vs 2.0 ton A/C.

Did I miss something; is this gas heat and air, or a HP with backup elec heat?

[teddy bear]

Hi guys:

My basement and home is tight. Real tight. I won't bore you with the details, but suffice it to say it is dry enough to lay hardwood. It's a walk out basement, rear wall only now below grade. HVAC calc gave conservative numbers for very low load (<1 ton IIRC). I have ~1700 ft2 and will have about 9 ducts to the floor plan.

The house has radon and a radon mitigation system. I'd like to add an ERV to supplement that system for peace of mind.

That's the parameters.

What unit is going to give me the best comfort levels, and efficiency in this well insulated, tight, waterproof basement?

Thanks!

With active radon system, I suggest a make-up air ventilation for the basement. Positive pressure reduces the negative pressure on the house from the stack effect. With more positive the pressure in the basement, the radon is less likely to enter the basement space. An ERV is a balance flow device, therefore no positive pressure and you still have a 50-60% moisture load. Using a ventilating dehumidifier to introduce a small amount of fresh air into the basement is ideal. I found 50-60 cfm of fresh air stops outside air from infiltrating and slows radon infiltration. The dehumidifier part of unit will maintain the ideal 50%RH during low/no load cooling weather. With TN weather, you will not have many cooling hours in the basement. My experience with basements is that they have no cooling load, but tend be cool because of the earth temperature and heat rises. As a kind friend said: teddy bear = thermastor.com. Check out the Ultra-Aire 90H. I have June basement data on my WI 1,700 sqft. basement. This type of equipment makes a basement the most comfortable space in a home. Regards TB

[shorton]

An ERV is a balance flow device, therefore no positive pressure and you still have a 50-60&#37; moisture load.
I am all for some make up air and one of the reasons I'm lookin at the ERV. The sealing was done in great detail, and I'm not getting much leakage from the house into the radon vaccum. I may get some stack effect infiltration from other places, though. The ERV's I'm looking at are adjustable actually to achieve positive pressure, I woudl not consider one that was not.

For my education, how do you arrive at the 50-60% expected moisture load?

But I'll consider your's too. But I still need to size the unit properly. How much load does your's add during peak summer and winter situations?

[shorton]

Answers:

>1) There was mention of computer(s); how many boxes, how many monitors, how many UPS power supplies, etc? My office has a lot of electronic equipment, I had to add an extra 6" duct to keep it comfortable in the summer.

Figure 2 monitors, 2 computers, 2 UPS, 1 large AMP, 3 misc low consumption compents, one projector. Figure usage of 2 hours per day max on AV equipment. 1 computer is 24x7. Haven't had time to inventory and do a detailed calc yet.

> Could you post the number of windows and doors, and rough sizes? THX.

The square footages for them adn their construction are inthe HVAC-calc output link I posted. But ina nutshell there are 3 doublehung windows, 1 sliding glass door. 1 exterior type door to conditioned space upstairs, 1 exterior type door to semi conditioned airlocked room.

> along with half a dozen warm bodies (maybe more, one never knows about these things)... the added capacity might be worth looking into.

I want to size for the norm. Norm is 4 bodies, max is 6. I get more than 6 in my house maybe once per year, maybe.

> The ERV unit will add outside air, so that air will need to be heated or cooled (possibly de-humidified) also.

Yes, but I haven't found a way to add that load to HVAC-calc, yet.

> And who knows if you might end up with an 'in law' living in the basement 'apartment' sometime down the road... :)

If they moved in, I'd move out :) I do not wish to plan for that.

> If it were me, I would definitely go with the VS (variable speed) blower, and work some more on the 1.5 vs 2.0 ton A/C.

I still don't see this stuff approaching 2 tons. But I'm no expert.

> Did I miss something; is this gas heat and air, or a HP with backup elec heat?

Natural gas heat. No elect heat.

Thanks, Scott

[bkcalhoun]

Bear,
I agree 100%. I think all homes should have fresh air introduced. It cuts down on the changes of a downdraft from natural draft applinaces among other things.
Shorton,
controlled outside air should not change your heat loss/gain calcs. You are only controlling infiltration through your conditioning unit not increasing it. All homes have infiltration. If you can infiltrate through your ac/heat unit and exfiltrate through the envelope of your house you will be more comfortable. Field controls makes a fresh air setup I belive it is an MAS It is a barometric damper which opens when the system is running and closes when it stops. It will also open if the pressure changes in the house. What I like about it is it is automatic and the only moving part is operated by gravity which never fails.

[beenthere]

With a 1.5 ton. You want a VS blower.
With York(and most brands) you will have a wide selection of CFMs.
With York, with teh 1, or the 1.5 ton condenser you can set it to 345CFM, 406CFM, 548CFM, 645CFM, etc for cooling CFM.
(yes, with York, you don't tell it CFM per ton, you just set it to the total CFM you want).
The blower doesn't care what condenser its connected to.

A VS blower isn't limited as much as a PSC blower.

Next. Your HVAC people are thinking that supply delivers X CFM no matter how long it is.
Thats incorrect.

The bedroom may only need 40CFM, the bathromm 20CFM, the play room 50CFM, the office 75CFM, and the theater room 220CFM.(I just pulled these numbers out of the air)

The theater room would be best served with larger supplies to keep the air noise down.

Keep in mind, that just because 2 rooms have the same size supply, doesn't mean they need or get the same CFM.

[ga-hvac-tech]

Been will probably disagree with me on this, but I would lean towards the 2 ton. The reason is the heat (heat to remove) load from the electronic equipment AND the fresh air to condition from the ERV unit.

If you choose to install the dehum unit Teddy Bear mentioned (including the positive pressure fresh air that has already been conditioned), then the 1.5 ton may work.

Yeah, it sounds like I am hedging, but without looking at it (live, not pictures), I really could not give you a firm answer.

If it were me, I still would do the VS furnace.

And while I am at it, I would go with the HoneyWell YTH 9421 thermostat. You can set up the 2 stage heat and the dehum cycle from the stat.

[shorton]

With a 1.5 ton. You want a VS blower.
With York(and most brands) you will have a wide selection of CFMs.
With York, with teh 1, or the 1.5 ton condenser you can set it to 345CFM, 406CFM, 548CFM, 645CFM, etc for cooling CFM.
(yes, with York, you don't tell it CFM per ton, you just set it to the total CFM you want).
The blower doesn't care what condenser its connected to.
Thanks, I'm stil a little fuzzy on the CFM to tonnage relationship. If it turns out that my loads are 1 ton, and I set such a 1.5 ton unit to ~400CFM, does it effectively become (or produce) 1 ton of cooling? If so I could adjust the unit to "fit" my load requirement.


Next. Your HVAC people are thinking that supply delivers X CFM no matter how long it is. Thats incorrect. Among other incorrect assumptions, yes I think so too. 5 different companies. Frustrating.


The theater room would be best served with larger supplies to keep the air noise down. Exactly. But when I suggested this to the various estimators, they did not want to do this at all. They insisted I needed to keep the air velocities at some rule of thumb level.


Keep in mind, that just because 2 rooms have the same size supply, doesn't mean they need or get the same CFM.Do you mean becasue of difference in friction losses of varying duct runs and the respective damper adjustmentss right?

Thanks, Scott

[shorton]

Been will probably disagree with me on this, but I would lean towards the 2 ton. The reason is the heat (heat to remove) load from the electronic equipment AND the fresh air to condition from the ERV unit.
Well, I'm still leaning toward the ERV. I have an unusually low need to remove moisture IMO.

And I think the 2 ton will come on, go poof and satisfy. It won't run long enough to circulate the air and remove what humidity there is, especially in the summer when the cooling load is low. This AV equipment is turned on for a max long enought to watch a movie. Then it's back off. I agree with TB and almost everyone agrees the cooling load will be low. So I'll have extra capacity to deal with some increase from the occasional relatively rare use of the AV stuff. And for heat, I'll have a lowered requirement it the eq puts off some heat.

But that's why I'm here to get some more professional opinions and input since I know enough to make me worry but not quite enough to argue my perceptions, yet :).

[shorton]

Bear,
I agree 100&#37;. I think all homes should have fresh air introduced. It cuts down on the changes of a downdraft from natural draft applinaces among other things.
Shorton,
controlled outside air should not change your heat loss/gain calcs. You are only controlling infiltration through your conditioning unit not increasing it. All homes have infiltration. If you can infiltrate through your ac/heat unit and exfiltrate through the envelope of your house you will be more comfortable. Field controls makes a fresh air setup I belive it is an MAS It is a barometric damper which opens when the system is running and closes when it stops. It will also open if the pressure changes in the house. What I like about it is it is automatic and the only moving part is operated by gravity which never fails.
Thanks. MAS? Edit, found it: Makeup Air system:
http://www.fieldcontrols.com/cas.php

Your suggestion brings up another point, perhaps for a different thread, but the whole family is suceptable to fall airborn alergens. So I need to filter whatever makup air comes in significantly. I don't want to "suck" alergens into the house on purpsoe :)

[beenthere]

Thanks, I'm stil a little fuzzy on the CFM to tonnage relationship. If it turns out that my loads are 1 ton, and I set such a 1.5 ton unit to ~400CFM, does it effectively become (or produce) 1 ton of cooling? If so I could adjust the unit to "fit" my load requirement.

I wouldn't set a 1.5 ton to run at 400 CFM only. That would be less then 270 CFM per ton, and would cause the coil to freeze up.
With the right control system, you can set up the system to vary its CFM by the humidity.

Among other incorrect assumptions, yes I think so too. 5 different companies. Frustrating.

Exactly. But when I suggested this to the various estimators, they did not want to do this at all. They insisted I needed to keep the air velocities at some rule of thumb level.

If the ducts are in the ceiling, you will need a higher velocity for heating. But for cooling it won't need to be as high. If they look at their ductulators, they may realize, that 4" and 5" supplies will give them their higher velocities. Instead of just using 6" supplies for everything.

Do you mean becasue of difference in friction losses of varying duct runs and the respective damper adjustmentss right?

Pretty much so, and because the bathroom won't need as much air as the bedroom.

Thanks, Scott

If you install a 2 ton, you will definitely want a whole house dehumidifier.

[ga-hvac-tech]

Well, I'm still leaning toward the ERV. I have an unusually low need to remove moisture IMO.

And I think the 2 ton will come on, go poof and satisfy. It won't run long enough to circulate the air and remove what humidity there is, especially in the summer when the cooling load is low. This AV equipment is turned on for a max long enought to watch a movie. Then it's back off. I agree with TB and almost everyone agrees the cooling load will be low. So I'll have extra capacity to deal with some increase from the occasional relatively rare use of the AV stuff. And for heat, I'll have a lowered requirement it the eq puts off some heat.

But that's why I'm here to get some more professional opinions and input since I know enough to make me worry but not quite enough to argue my perceptions, yet :).

Couple of things:

First, I would set the VS furnace at continuous fan. It will use a very small amount of electricity, yet it will keep the air circulated around the basement. The cooler (or warmer) air at the windows and doors, and the warm air from the computers and AV equipment (and the warm bodies while you are watching a movie), will be moved around and ultimately trigger the stat and start the system.

The rooms that are totally in the basement (totally IN the ground), will need less heating or cooling. The rooms that have a source of heat (computers, AV equipment, warm bodies) will need a little more air. The rooms that have exterior exposure (windows and doors) will need extra air also... I am referring to airflow.

The VS furnace should have what is called ODD (on demand dehumidification). What this does is lower the fan speed to soak up humidity when a humidistat says it is too high. This can also work as a low stage of cooling (Been will fuss about this also... LOL).

SOOO, you could have a little extra capacity for the heat loads, yet have a lowered capacity for normal operation.

And lets not forget: If there is a full bath and/or a kitchen down there, that will produce heat and humidity.

Lets think about something here: What would it be like if one skimped as much as possible, and then did not have enough air for a movie party? Not a good thing IMO.

Most of the basements I used to do were in the 1400-1800 ft area. Most of them worked well with 1.5 ton. But I also got a few call backs when an office full of electronic stuff was added to the basement.

I have a 3300 ft basement out there that required 2.5 tons. It has a full kitchen, two baths, a workout room, and a really fancy AV room. Two tons was just not enough... but that house is not as tight as yours is.

I think you need to find a qualified person to come out. Yeah, that will cost a few $$$... however I doubt you will be happy until you get that input.

Best to you on this one!

[bkcalhoun]

MAS will result in better indoor air quality. You are controlling where allergens are entering your house. They will be entering the return duct before the filter. Without it, regular infiltration comes in through doors, windows, utility penetrations etc.

[shorton]

I'm not looking to skimp. It dosen't seem to me that using a 1.5 tons unit for less than a 1 ton load is skimping. Unless the AV equipment adds a 1/2 ton of cooling load. I will calculate liberally to see.

Oversizing is the wrong thing to do though. It will casue other problems I think. And not be very comfortable, either.

[shorton]

MAS will result in better indoor air quality. You are controlling where allergens are entering your house. They will be entering the return duct before the filter. Without it, regular infiltration comes in through doors, windows, utility penetrations etc.I understand this part, and agree. Might even be decent in lieu of or to compliment an ERV.

[ga-hvac-tech]

I'm not looking to skimp. It dosen't seem to me that using a 1.5 tons unit for less than a 1 ton load is skimping. Unless the AV equipment adds a 1/2 ton of cooling load. I will calculate liberally to see.

Oversizing is the wrong thing to do though. It will casue other problems I think. And not be very comfortable, either.

Be sure you calculate in the computers... :)

[shorton]

Will do, thanks.

[teddy bear]

I am all for some make up air and one of the reasons I'm lookin at the ERV. The sealing was done in great detail, and I'm not getting much leakage from the house into the radon vaccum. I may get some stack effect infiltration from other places, though. The ERV's I'm looking at are adjustable actually to achieve positive pressure, I woudl not consider one that was not.

For my education, how do you arrive at the 50-60% expected moisture load?

But I'll consider your's too. But I still need to size the unit properly. How much load does your's add during peak summer and winter situations?
The amount of fresh air you need is less than 75 cfm. Unbalancing a 75 cfm ERV is not very effective at creating a positive pressure. Also bringing in more outside air will cause problems with freezing up the ERV. Recovering the heat in a small amount of exhaust air is less than $50 for the year. It really will not decrease the moisture load very much. Most do not realize that changing the air in a home every 5-6 hours is will make the home damp like the outside air. A TN basement will not have any cooling load except when fully occupied. No cooling load with fresh air ventilation means you need 2-3 lbs/hour of dehumidification. An ERV total balanced reduces the dehumidification load in your fresh by 40% provided you exhaust very dry air through the ERV. You must still remove the remaining moisture in the fresh air and from the occupants. Consider your investment in the ERV, the fans operating cost, the reduction in positive pressure, and that you still need a good dehumidifier before investing in both. 75 cfm of fresh air is about 6,000 btus/hour of cooling load on a hot day. About half of the cooling load is sensible and half latent. On a normal evening, the load drops to 3,000 btus of latent heat load. This is all moisture without any cooling load. With no cooling load, a good dehumidifier is a must. The Ultra-Air dehus have custom air filtering for the blended fresh/house air that is circulated back to the space. Regardless, do not short cut fresh air because of improved air filtering. Regards TB

[shorton]

TB:

Thanks. Good information. I registered my hvac-calc a little while ago so I can get a solid load calc as soon as they send the activation code. And I have my electronics summed up. As soon as I get the numbers, I'll try to put this all together for the best choice. Stay tuned...

Thanks, Scott

[shorton]

All:

I registered my hvac-calc and reran the reports. I was liberal in everything I could think of. I wasn't sure what to put of the basement ceiling that has conditioned space above it, so I tried both "unoccupied room with R57" and leaving that item off entirely. I got the higher loads with the first one so I left it at that.

I added all of my electronic components and they came to 2500w. I used the formula of 3.4 x 2500 which comes out to 8500 BTUH. But this will be an absolute maximum and rarely in place.

I used 6 people which will be high. I tried upping it to 8 and it didn't change it much.

For infiltration, I'm not sure what to feed it. It already shows a recommended amount which I accepted. So I added another 50 CFM. I also tried upping it to 75cfm per TB's input above. That added the most jump
(19.6kBTUH)

Of course I set the location to Nashville and accepted the defaults for here.

So no matter what I threw at it, it still appears to call for a 1.5 ton unit. And since many of these things will rarely be worst case, 1.5 ton looks good. I think.

Here is the HVAC-calc output. I don't think I made any errors. Some things aren't in there, like my walls are 10" solid concrete, not block or masonry, but I chose block as the best match:

http://www.companypostoffice.com/scott/hvac3.pdf


Is the matching 45k furnace enough?

Thanks, Scott

[beenthere]

Yea, 45,000BTU furnace is enough, and then some.

If you have the time this weekend.
If you measure up/enter off the prints each rooms demesions and windows and doors.
Plus enter the equipment for those rooms. HVAC Calc will also give you a room by room CFM report.

[bkcalhoun]

If you have conditioned space above you should eliminate that line from your calcs there is no heat loss or gain.

[bkcalhoun]

Yea, 45,000BTU furnace is enough, and then some.



If you go variable speed,it will most likely be a 2 stage furnace. disable the scond stage and it will more closely match your heat loss.

CFM per room reports in hvac calc are accurate, but ignore the duct sizing it is completely inaccurate.

[shorton]

beenthere: Will do as suggested and enter all the room details. That will be good info.

--------------
bkcalhoun:

Excellent. I do plan to get the variable speed. I think the furnace is 2 stage as well.

I will remove the conditioned space from my ceiling entry in HVAC-calc.

One thing I haven't mentioned or really factored into the calcs is that in the 1700ft2 I have been using, I have a sizable chunk that will have less load. I will have a fairly large mechanical room that includes the upstairs unit, downstairs unit and a water heater. I also have a large storage area that won't need much airflow, just enought to circulate the air. It can be cooler/warmer in there without issue.

Thanks for the tips. Much appreciated.


I also ordered a hygrometer today so I can get a ball park idea of what the humidity is like in the basement now. I think it's dry, but an instrument reading would be good, even if it's not the most accurate "instrument" (Extech). Too bad I didn't start this quoting and planning in the sumer when it would have been higher.

[beenthere]

Don't need to disable the second stage. If you use a 2 stage stat, it will only call for second stage coming out of recovery.

[bob_scheel]

Your projector bulb btus are 3.4 x 250 watts or about 850 btus. Other electrical loads like electronic systems you can use the nameplate amp draw and a fudge factor of about 75% if you do not actually measure the draw.

Lights are always 100% as all of the energy remains behind as heat.

[shorton]

Thanks Bob. I took the other things at 100%. I can lower those some.

I did not add anything in there for lights. Is it normal to add the lighting loads in hvac-calc?

Thanks, Scott

[bob_scheel]

Thanks Bob. I took the other things at 100%. I can lower those some.

I did not add anything in there for lights. Is it normal to add the lighting loads in hvac-calc?

Thanks, Scott

In commercial applications yes. In residential they usually don't contribute a lot to the cooling load because at peak load they are usually off. (sunlight) But in a basement especially with such a low load you should probably figure them in.

[shorton]

Thanks, I understand. That makes perfect sense I hadn't thought about the detail of why they aren't normally included.

[shorton]

Hi guys:

I did my homework and entered all my rooms in HVAC-calc. The square footage is off a little becasue I didn't include the equipment room that contains the equipment. It's surrounded on all 4 sides and ceiling by conditioned space, and I don't want to cool it anyway, so it shouldn't do much.

I did use the CFM by room calc and then the duct sizing program. Someone above said it didn't work well, but it seemed reasonable to me. If the CFM is right anyway. The only thing odd (to me) was it spec'd a 3" duct for a small bath I have, seems small. Particularly since the estimates I received had a 6" going into each side of it (bath side and sink side).

And it put a 4" duct in a small hallway. This hallway will essentially serve as the return air path for most of the rooms so I'm thinking I could either run no duct to it, or make it smaller, and maybe add some to the bathroom. Any advise regarding treatment of a hall that is a return air path would be appreciated.

I'd be grateful if you guys would take a look for a sanity check to see if the hvac-calc reports look reasonable. I sized it with a 1.5 ton unit. The Goodman I am looking at appears to be rated for 600CFM which is what I used in the calcs. If I add a bunch of lights or extra people loads I can get it to recommend a 2 ton. But, I have several mitigating factors that I just don't think that is necessary. And, I won't have people or lights on in every room all the time.

Here are links to the reports:

Details: (http://www.companypostoffice.com/scott/hvac4-load-details.pdf)

Sorted by heatgain/summary: (http://www.companypostoffice.com/scott/hvac4-heatgain.pdf)

CFM report: (http://www.companypostoffice.com/scott/hvac4-cfm.pdf)

Duct sizing: (http://www.companypostoffice.com/scott/hvac4-duct.pdf)

I think I have a contractor who will follow my decisions regarding sizes if I choose to dictate them, but I don't think they will be very comfortable with what these calcs say. But my upstairs unit's design bites, so I'd like to participate a little closer to see that at least the basement system gets built more properly.

Thanks very much for the help.

[shorton]

Hi guys: While checking for a reply I found my links abouve were not working properly. Hopefuly no one had tried to use them yet. If you did, I have corrected the links. If anyone could take a look at the HVAC-calc recommended duct sizes I'd be most grateful.

[beenthere]

The duct sizes, are virtually all TOO small.

You don't want to hear what 151CFM will sound like going through a 6" flex.

[shorton]

Thanks. Is it becasue their recommended velocities are too high and thus lead to the smaller, noiser sizes, or becasue their calculations are simply wrong?

What is the correct velocity for flex? I think it recommends 700fpm.

Is it possible to get good duct size recommendations from HVAC-calc, applying the proper "adjustment" (e.g. specify a slower velocity, or go up one size over the recommended, etc.)?

[beenthere]

Never really used its duct sizing feature.

It based on velocity only, and doesn't give consideration to the length of duct, for static pressure.

So besides velocity noise, you will have high static pressure, which depending how high, is not good for a VS blower. Can shorten its life span, and will cause it to use more electric then a standard blower motor.

[shorton]

Thanks. The techs around here do their complete design as far as I can tell with a ductalator. Given the CFM requirements of the room as provided by HVAC-calc, is that a good tool to do the proper sizing with? Is there another tool I can use to verify their design choices?

[adrianf]

a Manual D worksheet with total equivalent lengths and device pressure drops calculated.

[shorton]

Doesn't the Ductalator use the same method as Manual D? Equal friction design?

[shorton]

I've had a lot of help here and as my complete issue is larger than the original question, the thread has drifted off topic.

I have the answer to the original question, sort of. I'm more comfortable a high effiency unit wiht a variable speed blower woudl be a good thing for this space.

So I will start a new thread to ask about the duct sizing.

THANKS!

[adrianf]

Doesn't the Ductalator use the same method as Manual D? Equal friction design?


Once you determine the available static pressure that's when you get to play with the ductulator.

[shorton]

Continued this discussion in this new thread:

http://www.hvac-talk.com/vbb/showthread.php?p=2027733#post2027733