ACREX - 2013

Watch the video ACREX - 2013 on YouTube

I was in the ACREX-2013 exhibition held at Bombay Exhibition Center on 7th,8th & 9th in Mumbai. Watch the video above to get a feel.

Rules of Thumb in Refrigeration Engineering

The rules of thumb article below is a part in series of lecturers of Prithvi Datta (UK) ] he used at

Colleges of HE & FE in United Kingdom with practical experimentation for promoting innovation and

modification in R&HVAC Engineering.Thousands of Trainers of Trainees and students of courses from

Apprentice Mechanic to Ph.D. had appreciated the series to master skills for Experimental Studies

and Techniques.

Part 1

During my professional duties as Lecturer in R&AC in a Humberside college of HE&FE we

were using R12,22 or 502 for following use of Rule of Thumbs. I tried to use R410A for the

following example using limited data available to me at that moment.Selected R410 for this

application with COP of 8.33 is good example.

why some refrigerant cannot be used without waste of energy and operational and capital

losses.Phase & State of Refrigerant at important specific points within as simple

Refrigeration Cycle working in UK with R410A working at ambient temp. 25 deg for

refrigeration duty of - 20 deg. C (ignoring pressure drop caused within the pipework).

Refrigeration Cycle should be studied at 12 specific point in the cycle

with R410A working at ambient temp. 25 deg for refrigeration duty of - 20 deg. C Refrigeration Cycle should be studied at 12 specific point in the cycle

Ability to forecast State and Phase of Refrigerant at these 12 points and mastering P-h

Chart using these 12 points can allow true professionals to raise energy efficiency of

Refrigeration Systems and gain best of trouble shooting skills.

High Side of Cycle                   

Point Position                   State.        State.    Phase of Refrigerant
       
1. Inlet of Compressor               3               -18       Superheated Gas

2. Outlet of Compressor            25              80       Superheated Gas

3. Inlet to Condenser              25              70       Superheated Gas

4. 1/8 of Condenser               25               40       Saturated Vapour

5. ½ of Condenser                 25               40       45% Vapour +55% Liquid

6. 7/8 of Condenser               25               40       100% Saturated Liquid

7. Outlet of Condenser          25               33       Subcooled Liquid

8. Inlet of Metering device     25               32       Subcooled Liquid 

Low Side of Cycle                   

9. Outlet of MD                    3                -28       Liquid with Flash Gas

10. inlet of Evaporator        3                 -28       Liquid with Flash Gas


11. ½ of Evaporator            3                 -28       45% Liquid + 55% Vapour


12. Outlet of Evaporator     3                 -22       Superheated Gas

Please visit the site for the next post for the Part-2 of the Rules of Thumbs.

5 Wrongs At ACREX-2013

It is not only HVAC industry that should support energy conservation brigade but the trend in the whole world in any industry is such.There should be a strong movement in this direction.
 
Go Green - Environment friendly and the buzz word being "Dedicated to Eco Friendly Environment".
What rubbish !Ask ACREX-2013 organisers and visit the stalls of the companies you will find the vast difference between what is being propagated on the paper and what is the ground reality.
 
I was in ACREX-2013 exhibition held at Bombay Exhibition Center on 7th,8th & 9th in Mumbai.
I have attached the theme photo of the ACREX-2013 bill board that says "Dedicated to Eco Friendly Environment". The reality is far from the spirit of the theme.
 
The reasons are below:
 
1) I visited the stalls of the most big compressor manufacturers for the compressor requirement on "Natural Refrigerant" and couldn't find even a single manufacturer who could supply for the requirement.
 
2) We often talk of Renewable source of energy - Solar.The harsh reality is that most of the manufacturers are not ready to switch to this technology because of the captivity of their mind sets.
 
3) Companies are still using conventional HFC's and not ready to switch over.
 
4) No clear long term perspective from Small & Medium scale HVAC players.
 
5) No clear R&D guide lines on renewable source of energy use in present day environment.
 
I hear Australia has developed some of the solar energy concepts in HVAC and one of them I featured on my blog here and also at:
http://harshbardhanlive.wordpress.com/
where the energy being consumed is only 34 watts.
 
The need of the hour is to switch to more natural sources of energy and going green will be only possible when we change our mind sets and not merely on the bill boards as on ACREX-2013.

Feel free to comment on my post may be if your observation is different from mine I could change my outlook!

Energy Efficient - Solar Split Air Conditioner

 
Frazer Goodman has developed the next generation Split Air Conditioner that runs on Solar Power and consumes only 0.34 Watts.

HVAC System Design- Formulae

I have been approached by lot of people to teach them system design for the HVAC&R product development and I thought it fit for them to start from basics as without  solid foundation there can be no building.So I thought of compiling the basic formulae first and then go for the system design aspects.It has taken me considerable time to compile these formulae.
I would like to thank Ms. Ashima Saxena for helping me in editing the list of the compilation.

Thermodynamic Design Formulae
Sr. No.	EQUATION	FORMULAE
1	F = m a	Newton's law of motion
2	P = F / A	Pressure
3	ρ = m / V	Density
4	W = F d	Work
5	PE = m g H	Potential energy
6	KE = ½ m V2	Kinetic energy
7	Q = m Cp( t2 - t1 )	Sensible heat
8	Q = m ( h2 - h1 )	Total heat
9	W - Q = dE	1st law of thermodynamics
10	Cpa = 1.005 kJ/kgK	Heat capacity of dry air
11	Cpw = 4.193 kJ/kgK	Heat capacity of water
12	Cpv = 1.884 kJ/kgK	Heat capacity of water vapor
Heat Transfer Formulae
13	Q = - k A dt/dx	Conduction
14	Q = hc A ( ts - tf )	Convection
15	Q=σ A Fε FA (t1⁴-t2⁴)	Radiation
16	Re = ρ V Dh / µ	Reynolds number
17	Pr = µ Cp / k	Prandtl number
18	Nu = hc D / k	Nusselt number
19	Nu = 0.023 Re0.8 Pr0.4	Dittus-Boelter
Moist Air Phase Formulae
20	P = Pa + Pv	Dalton's Law of partial pressure
21	Pv = R T	Perfect gas law
22	Ra = 0.287 kJ/kgK	Gas constant of dry air
23	Rv = 0.4615 kJ/kgK	Gas constant of water vapor
24	W = 0.622 Pv / (P - Pv)	Humidity
25	Pv = P / [1+0.622/W]	Vapor pressure from humidity
26	r = (1+W) / v	True density of moist air
27	Ps = 0.6105 exp [ 17.27 t / (237.3+t) ]	Magnus saturation pressure
28	t = 237.3 / [17.27 / Ψ - 1] where Ψ = ln (Ps / 0.6105)	Dew point temperature using the Magnus equation
29	f = Pv / Ps	Relative humidity
30	Pv = Psw - 1.8( P- Psw )( db - wb )/( 2800 - 1.3 wb )	Carrier vapor pressure
31	H = 1.005 db + W [ 2500.6 + 1.85 db - 0.023 wb]	Enthalpy
32	hfg = 2501.9 - 2.4189 t	Latent heat of water vapor
Air Psychometric Formulae
33	ma = ρ Qa	Mass flow of dry air
34	Qs = ma Cpm ( t2 - t1 )	Sensible duty
35	Cpm = 1.023 kJ/kgK	at typical air-conditioning conditions
36	Qt = ma (h2 - h1 )	Total duty
37	SHR = Qs / Qt	Sensible heat ratio
38	b = ( db0 - adp ) / ( dbi - adp )	Bypass factor
39	Qs = h A (db - wb)	Sensible heat at wet wick
40	Ql = hd A (Ws,w - W) hfg,w	Latent heat at wet wick
41	hd = hc / Cpm	Mass transfer coefficient
Room Heat Formulae
42	Q = Uo Ao ( to - ti )	Heat conduction through a wall
43	r = ro + Σ t/K + ri	Wall resistance
44	Qsg = SHGF SC  A  CLF	Solar heat gain
45	Q = U A CLTD	Cooling load temperature difference method
Cold Room Formulae
46	Qpulldown = m C dT	Pull down load
47	Qlatent = m ∆W λ	Latent load
48	Qrespiration = m R	Heat of respiration
Solar Angle Formulae
49	d = 23.45 sin ( 360 (284+n) / 365)	Solar Declination
50	LST = CT + (Lstd - Lloc)/15 + E + DT	Local Solar Time
51	E = 0.165 sin 2B - 0.126 c os B - 0.025 sin B	Equation of Time
52	B = 360 (n- 81) / 364	Parameter in E
53	h = 15 (LST - 12)	Hour angle
54	sin β = cos l  c osh  cos d + sin l  sin d	Altitude angle
55	cos φ = (cos d  sin l  cos h - sin d  cos l) / cos β	Solar Azimuth
56	cos θ = cos β  cos λ  sin Σ + sin β  cos Σ	Angle to surface normal
Solar Radiation Formulae
57	IDN = A e -B / sin β	Direct Normal Solar Flux
58	IdH = C IDN	Diffuse Horizontal Solar Flux
59	ID = IDN cos θ	Direct Solar Flux on Surface
Coil Calculation Formulae
60	dQ = hd dA ( ha - hi )	Heat flow on the c oil air side
61	dQ = hr dAi ( ti - tr )	Heat flow on the c oil fluid side
62	dQs = hc dA ( ta - ti )	Air sensible heat
63	Q = U A lmtd	Duty from UA LMTD method
64	Lmtd = (dti - dto) / Ln( dti / dto )	Log mean temperature difference
65	Q = e Qmax	Effectiveness method
66	e = (1 - exp(- Ntu (1- Cr)) / (1 - Cr exp(- Ntu (1-Cr))	Counter-flow effectiveness
67	Cr = Cmin / Cmax	Capacity ratio
68	Ntu = U A / Cmin	Number of transfer units
Steam Formulae
69	λ = 2164 kJ/kgK	Latent heat of vaporization at 2 bar gauge pressure
70	λ = 333.6 kJ/kg	Latent heat of freezing
Fluid Flow in Pipes Formulae
71	dPfriction = ½ ρ ƒ L V2 / Dh	D'Arcy Weisbach friction equation
72	1/√ƒ = -2 Log [ ε / (3.7 Dh) + 2.51 / (Re √ƒ) ]	Colebrook friction factor
73	Dh = 4 A / P	Hydraulic diameter
Duct Design Calculation Formulae
74	P + ½ ρ V2 + ρ g H = constant	Bernoulli equation
75	P1 + ½ ρ V2 + r g H1 = P1 + ½ ρ V2 + ρ g H1 + Ploss	Modified Bernoulli
76	dP = ½ ρ Vd2 [ 0.4 ( 1 - Vd/Vu)2 ]	Branch straight through dp
77	Def = 1.3 (ab)0.625 / (a+b)0.25	Effective diameter of rectangular duct
78	dP = ½ ρ V2 [ (A1/A2)2 - 1 ]	dP for ideal flow through a nozzle
79	dP = ½ ρ V2 [ 1 - (A1/A2) ]2	dP for sudden enlargement
81	Re ≈ 67 V Dh	standard air with V (m/s) and Dh (mm)

Fan Laws
82	Law 1	ρ = const	Q ~ ω	SP  ~  ω2	Pw ~  ω3
83	Law 2	ω = c onst	Q = const	SP  ~  ρ	Pw ~   ρ
84	Law 3	ω  ~  1/√ρ	Q  ~  1/√ρ	SP = const	Pw ~  1/√ρ

Natural Refrigerant - Hydrocarbon

Hydrocarbons are refrigerants that can be used as an alternative to fluorocarbon
refrigerants in some refrigeration and air conditioning applications.
The term ‘Hydrocarbon’ encompasses following:
 A) Ethane (R170)
 B) Propane(R290)
 C) Butane (R600)
 D) Isobutane (R600a)
 E) Propylene (R1270)

Properties
1) Hydrocarbons are highly flammable.
2) They have a low toxicity.
3) Hydrocarbon refrigerants are fully compatible with nearly all lubricants commonly used
    in refrigeration and air conditioning systems. One major exception to this rule is
    lubricants containing silicone and silicate.

Comparison with HCFC
1) HVAC professionals have made a comparative study on the performance of hydrocarbon
    refrigerants R290, R600a and R1270 with that of HCFC refrigerant R22 and found that in
    comparison to R22, hydrocarbon refrigerants have similar or better ability.
2) An experiment on a new refrigerant blend comprising R134a (an HFC) and hydrocarbon
    refrigerants R600a and R290, with a view to finding a replacement for the CFC refrigerant
    R12 in domestic refrigerators. The experiment concluded that the blend has been identified
    as a promising alternative to be used as a refrigerant in a conventional R12 system and
    that the blend reduced energy consumption by 4 to 11%.
3) Hydrocarbon refrigerants generally are compatible with the materials used in systems
    designed for R22 and often can use the same or similar lubricants, however, their
    substitution requires significant attention to safety issues including application
    specific considerations.
4) It has been observed that no (one) refrigerant has been identified as a suitable
    alternative for most applications,though they identify that some refrigerant blends “offer
    good options”. Blends can be HFC/HFC or HFC/HC.
5) Hydrocarbons may be suitable in some applications, and may not be in others, so every
    application needs to be carefully assessed on its merits.

Safety Issues
1) As mentioned above, hydrocarbon refrigerants are flammable and therefore certain
    restrictions are placed on their use to ensure safety.
2) All electrical contacts must be sealed or non-sparking.
3) The refrigerant charge in a system below ground level must not exceed 1.0 kg.
4) Sealed systems not exceeding 0.25 kg can be sited in any location.
5) Systems with charges exceeding 0.25 kg must not be located anywhere where a sudden loss
    of refrigerant will raise the concentration in the room or occupied compartment above the
    practical limit (0.008 kg/m³)
6) Piping for systems exceeding 1.5 kg must be restricted to the room containing the
    refrigerant.
                       

Hospitals, prisons, theaters, supermarkets, schools, hotels, restaurants, dwellings	• Refrigerant charge must not exceed 1.5 kg per sealed system • Refrigerant charge must not exceed 5.0 kg in special machinery rooms for indirect systems
Offices, small shops, small restaurants, places for general manufacturing and where people work	• Refrigerant charge must not exceed 2.5 kg per sealed system • Refrigerant charge must not exceed 10.0 kg in special machinery rooms for indirect systems
Industrial, cold stores, dairies, abattoirs, non public areas of supermarkets	• Refrigerant charge must not exceed 10.0 kg in humanly occupied spaces • Refrigerant charge must not exceed 25.0 kg for systems with high pressure side in special machinery rooms • No restrictions are placed on the charge size if all parts of the system containing refrigerant are in a special machinery room or in open air

Corporate Acceptance
1) In Europe, many models of domestic refrigerators are charged with hydrocarbon
    refrigerant in the factory. It is estimated that there are at least 100,000,000 household
    refrigerators in use around the world containing hydrocarbon refrigerants.
2) Hydrocarbons have also been used in small air conditioning systems and cold drinking
    water dispensers.
3) Hydrocarbon refrigerants are also commonly used in large process refrigeration systems
    in the oil and gas industries.

Natural Refrigerant - Carbon dioxide

The use of Carbon dioxide (R744) as a refrigerant declined for a number of reasons, including
changes in technology and the introduction of fluorocarbon refrigerants, which were seen
as ‘safety refrigerants’.

Properties
A) Carbon dioxide has an ozone depletion potential (OPD) of zero and a global warming
     potential (GWP) of 1.
B) It is generally regarded as a cheap and easily available refrigerant, and many regard
     it as an ideal refrigerant.
C) Carbon dioxide is non-toxic. It has low toxicity and is non-flammable.
D) Carbon dioxide is colorless, odorless and is also heavier than air.If enough carbon
     dioxide builds up in an enclosed space it will begin to displace oxygen and can cause
     asphyxiation in anyone present within the space. As carbon dioxide is colorless and
     odorless, a person in the space will not be able to tell unless proper detectors and
     alarms are installed.
E) As a refrigerant, carbon dioxide operates at a higher pressure than fluorocarbons and
     other refrigerants. While this presents design challenges it can usually be overcome in
     systems designed specifically in suction and discharge tubing.
F) Carbon dioxide is not compatible with commonly used refrigeration system lubricants.It
     is not suited for use with polyol ester (POE) and poly vinyl ether (PVE) lubricants, and
     it has only limited applications with poly alkylene glycol (PAG) lubricants.

Safety Issues
A) Some restrictions are placed on the size of the refrigerant charge, with additional
     allowances made for systems with detectors and alarms fitted, and as carbon dioxide is
     heavier than air the standard requires “suitable precautions” to be taken to prevent the
     undue accumulation of refrigerant in occupied spaces in the event of a leak.
B) As with fluorocarbon refrigerants, the standard also requires the system to be designed
     to withstand the refrigerant’s maximum operating pressure.
C) The International Institute of Refrigeration (IIR) identified carbon dioxide’s high
     working pressure as the main drawback to its use.


Thermodynamic Properties
1) Carbon dioxide is colorless. At low concentrations, the gas is odorless. At higher
     concentrations it has a sharp, acidic odor.
2) At standard temperature and pressure, the density of carbon dioxide is around 1.98
     kg/m3, about 1.5 times that of air.
3) Carbon dioxide has no liquid state at pressures below 5.1 standard atmospheres (520
     kPa). At 1 atmosphere the gas deposits directly to a solid at temperatures below −78.5 °C
     and the solid sublimes directly to a gas above −78.5 °C. In its solid state, carbon
     dioxide is commonly called dry ice.
4) Liquid carbon dioxide forms only at pressures above 5.1 atm; the triple point of carbon
     dioxide is about 518 kPa at −56.6 °C.The critical point is 7.38 MPa at 31.1 °C.

Corporate Acceptance
Coca Cola company stated that the company’s preliminary field tests proved the technology
to be reliable, in real life circumstances the equipment often used less energy than
equivalent equipment using HFC as a refrigerant.
Till 2006, the company was market testing a range of drinks fridges and vending machines
using carbon dioxide refrigerants.