HVAC solution and calculation emergency help needed 1

[jakaodrz]

Hi and greetings to all of You.
As e new one I have a serious problem:

1. I have 2 systems to compare: The one is 100% fresh air (input), with build in coil recovery energy loop on exit side. The second is a system with 20% of fresh air with no energy recovery device on it.

How to make a decision which one is a better (this HVAC system are two different solutions for our pharmaceutical factory with class 100.000).
I've searched thru this forum, and find something, but as a new, i did not understand your units (american vs euro), and the way you calculate the difference between this systems.
The only thing I have to do is to calculate (formulas and suggestions)energy needed for heating (cooling) input air, to make a constant temperature of app. 22 degrees centigrades, and RH of 50%.

Maximum summer and winter temperatures are -20 and +40 degrees centigrades.

Also I've DL PSYCHROMETRIC ANALYZER, and tried to calculate it, but it do not include the energy of energy loop.
I have to mention that this is only for this time and no need for further comparement than this one.

Any help is a very big help to me.

Thanx in advance.

 

[sethuME]

hi
i dont think that 100% fresh air is needed for the class 100000 area.because going for 100% will increase your cooling load.

 

[ChrisConley]

Regardless of how you deliver outside air, the system will require the same amount of energy to cool and heat the air. The only way to decrease this energy is to use heat recovery.

If your space requires 1000 cfm (cubic feet per minute) of outdoor air then it will take 97,200 Btu/hr to heat that air from -20 to 70 F. If you mix 1000 cfm of OA with 9000 cfm of return air, it will still take 108,000 Btu/hr of additional energy to heat the air back to 70 F.

Which system is better? Tell us more about what you are trying to do, use whatever units you feel comfortable with; we can convert. How much air or air changes are you trying to do. Are you heating or cooling with the air, or is this just for ventilation.

 

[HVAC68]

Why are you trying to use a 100% fresh air and then using a heat recovery system ? Is 100% fresh air a process requirement ?

As ChrisConley has said, units are not a problem - we can convert.

HVAC68

 

[friartuck]

The amount of fresh air will depend on the occupancy and the process.

generally you can recirc a lot of the air to reduce the energy costs. This is much more effective/efficient than having a heat recovery loop and 100% fresh air.

On a lot of clean room projects we have seen, the fresh air is only about 10% to 15%.

I'm not sure how ChrisConley works out that the fresh air component does not affect the energy use. If you recirc 100%, then the load is simply the heat gain from the space. If you bring fresh air in, you have to add this component, which could be far greater than the room load. (hence recirc air is a good method of reducing the overall load)





Friar Tuck of Sherwood

 

[HEC]

Another thing to consider in this is filter loadings. Although only trying to maintain Class 100,000 standard, filtration of return air may be cleaner, than filtration of outside air. Of course this depands upon the process in the room. Dusty processes wouold be better with once through.
Energy usage will be a large part of the design choice, however also consider other aspects of the operation such as filters, replacement or cleaning, overall facility air flow requirements and pressure gradients, etc, etc.

Regards
Hutton4eng@picknowl.com.au

Mark Hutton

 

[jakaodrz]

First at all. Thax for everyone for a quick answer.
Second:
1.Chris Conley: I don't think that it is the same coling/heating energy that we are using for the both systems.Why? Because I think energy needed for 100% fresh air is not the same as the one for 20%.
2.OK, let's say ( TO ALL):
I need 100 metercubic/minute for all rooms.
Temperature for rooms is 25 degrees C, with 50% RH.
a. The 100% fresh air system: I need a load of 100 metercubic/minute for all rooms. What is needed energy (in kW) to make needed air, if we suppose that outdoor air is with -15 degrees C, thru winter ? And needed energy in summer, with outdoor air of +36 degrees C ? Also a use of coil type of energy recover is included in a system of exsaust air from the factory.
b. The system with 20% income and 80% recirculating air. The same calculations are valid (100 mcc/minute for rooms, -15C in winter and +36C in summer).

I need just fact (formulas) how can we calculate it but fast.
Just have to mention that this is a need for deciding what type of system to use in our new pharmaceutical factory, and the first criteria is economic side of energy used for both systems, and the second the maintenance of the system. The factory is class 100000.
Also, results using Psychrom program from Mcquay shows me that needed energy isn't same. But this is just for a drybulb type. With energy recover I do not know the results.

Greetings.

 

[ChrisConley]

Friartuck,

I didn't say that the fresh air component didn't make a difference. What I said was that regardless on how you deliver 1000 cfm you have to heat/cool it the same amount.

If we are moving air to provide a level of filtration, or course it will be less expensive to provide 20% outdoor air.
I'm comparing a DOAS (Dedicated Outdoor Air System) with heat recovery to a recirc system with the same fresh air requirements.

 

[quark]

The best heat recovery systems operate at an efficiency of 90%. So, you have to cough up 10% more energy cost.

Further, for room pressurization and fresh air requirement, you have to bleed off required quantity from rooms either if you go with recirculatory system or fresh air system. For a conservative comparision you have to deduct this energy component also(i.e approximately 10% volume rate of air is not available for energy recovery).

Regards,

 

[jakaodrz]

TO: ChrisConley

Let's do this problem together:
as you know, 2 system are in valuation.

The problem why I'm asking a formula (a simple one), to calculate input energy is that "somebody" is telling me that using 100% fresh air is cheaper than using 20-80% combination.
The 100% system have in
a)input side:intake section, filter F8, Run around system recovery (heating) with eff. of 30.4%, Centrifugal fan belt driven, diffusor, filter H13 and sound attenuator.
b)output side: sound attenuator, filter F7, run around system recovery (cooling), and outlet section with centrifugal fan belt driven.

I was told, that, if I'm using this type of HVAC solution, with combination of cooling plant with air compressors ventilation (dry){Correct me about my explanation of cooling plant}, my energy savings will be big, according to GMP requirements we are looking for. The controlled values are temperature, humidity and pressure. According to T, and RH of the output, also including outside conditions, the system needs (do not needs) some additional air preparations of intake air. The out take air is not needed any more, but for colleting of waste energy.

The point is, comparing to recirc system, where additional preparation of out take air is a must (filtration, dehumidification, heating, cooling), the control points are much more then the other, I will save money in start and the payback is much shorter. Lower energy costs ? In a future there is a chance to upgrade do class 10000 with only adding terminal HEPA filters and nothing more?

To help You, the conditions of the placement of the plant is on around 423 m (1391 ft, with approximate 65% of sunny days, and temperature variations from -20 to +40 C.

Thanx,

I'm just confused.

 

[quark]

Didn't get what you mean by cooling plant with air compressor ventilation. Nevertheless, 'somebody' is playing wrong.

 

[jakaodrz]

To: Quark

Ok, I know that the best heat recovery systems work at 90% eff., but the eff. of included recovery system is around 30% (technical factory written info).

It's filled with ethylen, with med.flow of 3.72 l/s, medium in 14.46C, med.out -1.42C. Air in -10C, air out 0.34C (this is for heating side), with 111 Pa pressure drop. capacity 233.28 kW. Medium press drop 45.34 kPa.
The cooling side is: air in 35C, 40% Hum., out 16.01 with 88% hum, air pressure drop 156 Pa, capacity 656 kW SHR. Medium ethylen, flow 33.298 l/s, med.in 5C, med.out 10C, medium press drop 32.79 kPa.


QUOTED:
"Further, for room pressurization and fresh air requirement, you have to bleed off required quantity from rooms either if you go with recirculatory system or fresh air system. For a conservative comparision you have to deduct this energy component also(i.e approximately 10% volume rate of air is not available for energy recovery)."

I do not understand well this: You mean that the quantity of air taken from rooms in both situations is the same, but additional processing of recirc air is a must in system 20-80%.
It is OK, I know that, but still the question is : how much energy will be used in both situations expressed in kW (let's say for 10000 m3/h) in both ways: with 100% fresh air, and with 20-80% recirc air system?

Thanx.

 

[quark]

I will try to simplify the things.

First, for room pressurization, say, you may require 10% of air flowrate. So this will be directly exhausted from the rooms and you won't get it back in the AHUs. This is compensated by fresh air intake in the second cycle.

When we consider 100% fresh air system, you will have only 90% appearing at the heat recovery unit. Considering 30% efficiency of the heat recovery system, you need not cool or heat 30% of 90% of total air flow(or 27% of total air flow).

When you use a recirculatory system with 10% fresh air, you should cool/heat 10% volume rate from ambient conditions to coil ADP and 90% from room condition to ADP.

With a heat recovery unit, it is (100-27)= 73% volume rate from ambient condition to coil ADP. So, compare 63%(i.e73%-10%) flowrate with ambient condition to ADP vs 90% flowrate with room condition to coil ADP.

Regards,

 

[jakaodrz]

TO: qUARK

Cooling plant (Cold water 5/10C) from Carrier-France type 30GX 082-358 or 30HXC 080-375.
Air cooled liquid chiller capacity 2x1000kW.
The coorect name is: Screw compressor water-cooled Liquid Chillers and air-cooled liquid chillers.

This is what a meant of cooling plant.

greets

 

[jakaodrz]

To: Quark
Ok, I'll quote your message and do it step by step:


"First, for room pressurization, say, you may require 10% of air flowrate. So this will be directly exhausted from the rooms and you won't get it back in the AHUs. This is compensated by fresh air intake in the second cycle."

First: This is for recirculating system or it is for both systems?
Let's say: 1000m3/h - 10% = 900 m3/h, right ?

"When we consider 100% fresh air system, you will have only 90% appearing at the heat recovery unit. Considering 30% efficiency of the heat recovery system, you need not cool or heat 30% of 90% of total air flow(or 27% of total air flow). "

Ok, if we suppose that above is corect and for both systems:
900 m3/h - 30% = 270 m3/h of total input flow to heat with recovery unit, right ? The other 730 (or 630) m3/h have to be heated with heating-cooling unit, ok ?

270 m3/h - recovery unit
730(630) m3/h - heating cooling unit


"When you use a recirculatory system with 10% fresh air, you should cool/heat 10% volume rate from ambient conditions to coil ADP and 90% from room condition to ADP."

In this case I need 100 m3/h to heat from outdoor air, and another 900 m3/h to heat-cold from room air ? What is ADP ?

"With a heat recovery unit, it is (100-27)= 73% volume rate from ambient condition to coil ADP. So, compare 63%(i.e73%-10%) flowrate with ambient condition to ADP vs 90% flowrate with room condition to coil ADP."

I'm stuck here at the last point Help.
You mean:
- 270 m3/h heated with recovery coil and 730 m3/h heated with heater in hvac, and for secure reason it is lowered to 63% of outdoor air?

You mean to compare 63% outdoor air to take heated and 90% of recirculated air to take heated ?
If I misunderstood correct me.

Greets,

 

[jakaodrz]

I'm stuck. Can somebody just say: You'll need this and this formula, or this program (free if possible ), and no fear. Job is done in a minute.

greets

 

[jakaodrz]

Or just using informations above for my problem (2-3 messages above this), and help me for right solutions.
The "catch" is in the price of both systems, which one to buy, and in my opinion is that in the system with 100% fresh air, must be something that I'm missing, which influence of the lower costs of whole HVAC solution.

That's why I'm asking for help, to do a fast calc of energy used in both system, for same quantity of air, for cooling and for heating. In fact, this became so confusing, that I do not know where to start and where to end. I've tried lot of programs (freeware, shareware,demo but no use) to find out the right one, where I can enter needed air in m3/h, to choose one, then the other system, and to read out and compare the given results (usage of energy in kW, for cooling and for heating).

So, if somebody have this type of program (it is doesn't matter whenever I know it or not), let just enter needed info which can be find in messages above, and give me a simple answer: In 1st system you'll need ...kW of energy for heating and cooling, and in 2nd system you'll need ...kW of energy. I'm not asking nothing more and nothing less.
Just to mention that this is my first contact with HVAC problem, solutions (maybe constructions) and simply I can't manage as good as you can here, experiensed engineers.

I hope You'll understand in what kind of trouble I am

Greets,

 

[quark]

Say, you have 1000cmh requirement.

With fresh air

First cool 1000cmh from ambient condition to coil condition(or Apparatus Dew Point). 10% is wasted in both cases, i.e 100cmh. So 900 cmh is present for recovery. Out of this you can avail 30% of heat, which is about 270cmh. This is as if you need not condition this much flowrate from ambient to coil condition. So what you have to treat is 1000-270 = 730cmh. - (1)

With recirculation

100cmh air is at ambient condition and 900cmh is at room condition. So you have to cool 100cmh from ambient condition to coil condition and 900cmh from room condition to coil condition - (2)

For your comparison 100cmh fresh air treatment is common. So deduct this from both options.

So, the fresh air option becomes treating (730-100)=630cmh from ambient condition to coil condition and recirculatory system option becomes treating 900cmh from room condition to coil condition.

The formulae

H1 is ambient air enthalpy in btu/lb
H2 is room air enthalpy in btu/lb and
H3 is enthalpy of air at coil exit in btu/lb

So, fresh air energy(for comparision) is 4.5x(H1-H3)x370.8cfm(i.e 630cmh) - (3)

Recirculation air energy is 4.5x(H2-H3)x529.72cfm(i.e 900cmh) - (4)

The lower value of (3) and (4) is your ultimate choice.

Hope I cleared the issue.

Regards,

 

[quark]

On a second reading, you seem to have grasped what I said perfectly except 630cmh thing, which I cleared in my third post.

Regards,

 

[jakaodrz]

Oh, thank You Quark, very much. This is a real thing. Except for one thing (quoted):

"H1 is ambient air enthalpy in btu/lb
H2 is room air enthalpy in btu/lb and
H3 is enthalpy of air at coil exit in btu/lb

So, fresh air energy(for comparision) is 4.5x(H1-H3)x370.8cfm(i.e 630cmh) - (3)

Recirculation air energy is 4.5x(H2-H3)x529.72cfm(i.e 900cmh) - (4) "

The values for H1, H2 and H3 where can be get ?
Especially in btu/lb. Also, isn't any changes if in formulae are used different valuses of units (ex. btu/lb and cmh) ?

Greets,