VT DIRECT EXPANSION DRYERS

Almost every area of manufacturing requires compressed air as a fundamental part of the production process. This has resulted with approximately 10% of the whole electrical consumption for UK industry being used to generate compressed air.

A typical compressed air system wastes approximately 35% due to leaks and these leaks are mainly due to corrosion that has been caused by wet compressed air. Further financial losses are incurred due to product spoilage and equipment downtime caused by wet compressed air. So why put up with it?

The Vortex Technology (VT) range of compressed air dryers can efficiently and effectively remove moisture from the air stream and therefore increase profits. The patented ‘monobloc’ design provides a simple and compact heat exchanger that reduces pressure drop across the dryer, thereby increasing overall efficiency. Every VT dryer is fitted with a monobloc heat exchanger, therefore every VT dryer affords the same level of efficient protection for your compressed air system.

Minimal energy consumption is vitally important in today’s competitive marketplace and purchasing a VT dryer will help you drive down your energy costs by minimising pressure drop and lowering absorbed power.

Direct expansion or chilled mass?

There are two basic type of refrigerated air dryer, chilled mass and direct expansion. All VT dryers use the principle of direct expansion as this provides precise control of the refrigeration temperature. Therefore a VT direct expansion dryer ensures a constant 3 deg C pressure dewpoint for fluctuating air flow rates that vary between 0% to 100% of rated dryer capacity.

The alternative is a chilled mass dryer, this is sometimes referred to as a ‘cycling dryer’. The refrigeration circuit in this type of dryer is used to cool a ‘third party’ material such as sand, glycol or aluminium chippings. The refrigeration compressor then switches off when a minimum set temperature such as 3 deg C is reached. The compressed air heat exchanger is immersed in this chilled mass and secondary heat transfer takes place between the chilled mass and the compressed air. Slowly the temperature of the chilled mass creeps towards an upper set point such as 10 deg C and then the refrigeration compressor switches back on again to cool the mass back down again.

Spot the difference?

Direct expansion dryers provide a constant pressure dewpoint within the normal operating parameters of a refrigerant control system. The control system used on all VT dryers ensures a constant pressure dewpoint of 3 deg C. The chilled mass dryer as described above would provide a cycling pressure dewpoint that fluctuates between 3 deg C and 10 deg C. Bearing in mind that you are buying a dryer to provide you with high quality compressed air, why settle for a less than ideal pressure dewpoint?

Energy consumption should also be considered. The refrigeration compressors fitted to all VT dryers are sized to handle the maximum rated flow for that particular dryer. By design the refrigeration compressor fitted to a chilled mass dryer has to be larger.

Why?

Because not only does the refrigeration compressor have to cool down the compressed air passing through the dryer, it must also have sufficient additional capacity to cool down the (now warm) chilled mass from 10 deg C to 3 deg C.

The effect of this can be considerable. If we look at a theoretical 5 kW direct expansion dryer, the most that this dryer will consume is 5 kW, even when operating at full load. A cycling dryer will also consume 5 kW to cool down the same volume of compressed air, plus another 2.5 kW or so to cool down the chilled mass from 10 deg C to 3 deg C. This is why the refrigeration compressor in a chilled mass dryer has to be bigger. On the plus side, the chilled mass dryer will switch off when it has reached the minimum temperature of 3 deg C, despite having consumed 50% more power whilst it was running.

In fact a direct expansion dryer will consume less power than a chilled mass dryer when both are operating continuously at full load. In reality the overall energy differences between both types of dryer are minimal, unless the chilled mass air dryer operates at only 25% to 50% of its rated capacity. However, the answer to this is fairly simple, buy the right size dryer in the first place.

We should not lose sight of the fact that a typical refrigerated air dryer consumes less than 2% of the electrical energy consumed by the matching air compressor. Therefore better savings can be realised by focussing upon the air compressor and distribution system.

One of the greatest energy savings of all is to avoid air leaks and to reduce pressure losses in the distribution system. Corrosion creates leaks and causes high pressure drops in pipework. Every 140 millibar (2 psi) of pressure drop is equivalent to 1% of the power consumed by the compressor.

Corrosion.

Steel needs two components to cause corrosion, moisture and oxygen. Compressed air contains both of these, therefore pipework will inevitably rust from the inside out unless preventative measures are taken. Screwed threads are the first point of attack as plating or painting has been removed by the action of cutting the screw threads. The two interfacing pipe threads set up a small electrolytic effect due to trace acids in the compressor condensate, thereby accelerating the effect of corrosion.

Rusting commences on ferrous metal when the relative humidity (RH) of air exceeds approximately 30%. At this point oxidisation is slight, however serious corrosion commences when the RH exceeds 60%. It therefore seems logical that keeping the RH of the compressed air at or below 60% would be desirable.

Consider two identical factories, one using a VT dryer and the other using a chilled mass dryer.

Using a VT dryer with a 3 deg C pressure dewpoint, the RH of the compressed air will vary from 45% during the winter months to 33% in the summer months. This assumes a typical factory with standard working conditions and ventilation.

Using a chilled mass dryer with a pressure dewpoint that cycles between 3 deg C and 10 deg C, the RH of the compressed air will vary from 72% in the winter months to 53% in the summer months based upon exactly the same parameters. Therefore installing a VT dryer will offer greater protection against rusty pipework than a dryer with a cycling dewpoint.

Features:

Constant 3 deg C pressure dewpoint
Maximum 16 barg operation
Low pressure drop
Reliable control system
CE certified and PED compliant
Environmentally friendly refrigerants

Model No.	Flow rate at 7 barg		Conn.	Power	No.	Fridge	mm	mm	mm	Weight	LIST
	Cu.m/h	CFM	BSP	kW	Phases	Gas	Height	Length	Width	Kg	£GBP
VT15	11	7	1/2	0.15	1	R134a	345	502	363	25	435
VT20	16	10	1/2	0.17	1	R134a	345	502	363	25	435
VT30	29	17	1/2	0.20	1	R134a	345	502	363	25	435
VT50	44	26	1/2	0.22	1	R134a	345	502	363	30	442
VT70	68	40	3/4	0.25	1	R134a	479	677	410	43	584
VT100	97	57	3/4	0.30	1	R134a	479	677	410	47	653
VT130	133	78	3/4	0.50	1	R134a	479	677	410	50	735
VT160	155	91	3/4	0.60	1	R134a	479	677	410	55	770
VT220	216	127	1 1/4	0.70	1	R134a	600	700	490	66	960
VT270	270	159	1 1/4	1.00	1	R134a	600	700	490	75	1110
VT330	324	191	1 1/4	1.20	1	R134a	600	700	490	80	1159
VT430	432	254	1 1/2	1.20	1	R134a	844	550	670	120	1660
VT500	504	297	2	1.20	1	R134a	1100	695	752	150	1840
VT630	630	371	2	1.20	1	R134a	1100	695	752	170	2339
VT870	864	509	2	1.60	3	R134a	1100	695	752	195	2760
VT950	936	551	3	1.60	3	R134a	1325	700	800	250	3593
VT1100	1098	646	3	2.10	3	R134a	1325	700	800	280	4111
VT1300	1260	742	3	2.10	3	R134a	1325	700	800	350	4548
VT1500	1440	848	3	2.70	3	R134a	1420	1120	1000	450	4931
VT1700	1710	1006	3	3.40	3	R134a	1360	1120	1000	460	5311
VT2100	2088	1229	3	4.30	3	R404a	1360	1120	1000	500	5695
VT2300	2304	1356	3	4.70	3	R404a	1360	1400	1000	525	6113
VT2700	2664	1568	4	5.20	3	R404a	1460	1400	1120	560	7222
VT3200	3132	1843	4	6.10	3	R404a	1460	1400	1120	600	8042
VT4100	4068	2394	4	7.20	3	R404a	1460	1480	1500	770	9224
VT4700	4680	2755	DN150	8.40	3	R404a	1460	1480	1500	820	10790
VT5600	5580	3284	DN150	10.10	3	R404a	1800	1800	1500	940	12608
VT6300	6300	3708	DN150	12.10	3	R404a	1800	1800	1500	1000	14391
VT7200	7200	4238	DN150	14.00	3	R404a	1800	1800	1500	1050	16362

Correction Factors
Pressure (bar) Factor F1	4 1.25	5 1.14	6 1.06	7 1	8 0.96	10 0.9	12 0.86	14 0.82	16 0.8
Ambient Temp deg C Factor F2	10 0.92	15 0.92	20 0.92	25 1	30 1.07	35 1.14	40 1.22	43 1.28	45 n/a
Inlet air temp deg C Factor F3	20 0.85	25 0.85	30 0.85	35 1	40 1.18	45 1.39	50 1.67	55 n/a	60 n/a

How to select a VT dryer:

Determine your required maximum airflow

Select your correction factors for pressure, ambient temperature, inlet air temperature.

Corrected flow = maximum airflow x F1 x F2 x F3.

Example. Required airflow = 265 cu.m/h at 8 barg with an ambient air temperature

of 35 deg C and a compressed air temperature of 45 deg C.

Corrected flow = 265 x 0.96 x 1.14 x 1.39 = 403 cu.m/h

Both the VT270 and the VT330 are too small. Choose the VT430.

Performance figures based upon 7 barg working pressure, 3 deg C pressure dewpoint, 25 deg C ambient air temperature and 35 deg C compressed air inlet temperature. All data refers to ISO-7183 & 8573-1.

Standard Features:
Dewpoint indicator
Electronic condensate drain
Power on light.
Zinc plated and powder-coated cabinets
Additional instrumentation for larger models.

Optional Extras:
50 barg operation
High temperature operation
60Hz supply voltage
In-line filtration
Water cooled condensers (larger dryers only)

Air & Gas Filtration

Air Treatment

Quality Control that Matters

Filtration - get the Technical Facts

Filterworld Pricelist
Filterworld Product Range 2007

VT DIRECT EXPANSION DRYERS

Direct expansion or chilled mass?

Spot the difference?

Why?

Corrosion.

Correction Factors

How to select a VT dryer:

Air & Gas Filtration

Air Treatment

Quality Control that Matters

Filtration - get the Technical Facts

Filterworld Pricelist Filterworld Product Range 2007

VT DIRECT EXPANSION DRYERS

Direct expansion or chilled mass?

Spot the difference?

Why?

Corrosion.

Correction Factors

How to select a VT dryer:

Filterworld Pricelist
Filterworld Product Range 2007