Siemens POWERS HU 186 Owner's manual

POWERS
TM
Controls
Technical Instructions
Document No. 155-027P25
HU 186-1
February 14, 2005
HU 186 Room And Duct
Hygrostats
Figure 1. Room Hygrostat.
Figure 2. Duct Hygrostat.
Siemens Industry, Inc.
Description The HU 186 Room and Duct Hygrostats are pneumatic instruments sensitive to slight
changes in relative humidity. They feature adjustable sensitivity and bimetal temperature
compensation to minimize temperature effects. The room hygrostat comes complete with
standard cover and wall plate. The duct hygrostat is shipped inside the duct mounting
box.
Product Numbers See Table 1.
Application The sensing element of the HU 186 hygrostat consists of a highly sensitive hygroscopic
membrane. Typical applications include comfort control of hospitals, schools, and office
buildings. More critical applications include the control of humidity in museums or
computer rooms.
Figure 3 shows a typical application of a room type hygrostat. The duct hygrostat would
be used when humidity sensing is to be done with a duct sensor. For most applications,
the best location for a duct sensor is in the return air duct.
Figure 3. Application of Room Hygrostat.

Technical Instructions HU 186 Room and Duct Hygrostats
Document Number 155-027P25
February 14, 2005
Page 2 Siemens Industry, Inc.
Table 1. Product Numbers.
Product Numbers Model Maximum
Dry Bulb Temp.
Control
Range (rh)
Direct Action
Reverse Action
186-0013 186-0019 Room 135°F 20 to 90%
186-0087 186-0088 Duct
- 186-0090 140°F 55 to 95%
- 186-0091 25 to 65%
Specifications
Operating
Physical
Direct or Reverse Acting Range See Table 1
Maximum Operating Temperature See Table 1
Sensitivity (adjustable) 1/4 to 4 psi per 1% rh
(1.7 to 28 kPa per 1% rh)
Normal Supply Pressure 15 to 25 psig (103 to 172 kPa)
Maximum Supply Pressure 30 psig (207 kPa)
Air Consumption 20 scim (5.5 ml/s)
Effect of 10° F Temperature Change Shift of 1% rh
Effect of 5 psi Supply Pressure Change
(mid-sensitivity) Shift of 1% rh
Air Capacity (time rating per 155-202P25
(TB-113) 0.7 min/vol unit
Dimensions, Room Type See Figure 9
Standard Room Cover Finish Desert Beige
Dimensions, Duct Type See Figure 10
Air Connections Barb fitting for 1/4-inch
(6.4 mm) OD Poly Tubing
Accessories Membrane Element Kit 186-062
Restrictor Plate Kit (Pkg. of 10) 180-893
Calibration Tool (Pkg. of 5) 192-632

HU 186 Room and Duct Hygrostats Technical Instructions
Document Number 155-027P25
February 14, 2005
Siemens Industry, Inc. Page 3
Operation
Reverse Acting
The action consists of a combination of force-balance and flappernozzle characteristics with
internal feedback.
A decrease in humidity causes the membrane sensing element to shrink. The contracting
element, which is attached to the element lever, exerts greater force on the nozzle lever
through the sensitivity adjustment assembly. The nozzle lever closes off the nozzle, building
up pressure above the relay diaphragm. Movement of the diaphragm closes the exhaust
valve and opens the supply valve ball. Supply pressure passes into the control pressure
chamber below the diaphragm. The control pressure increases until its upward force on the
diaphragm is balanced by the pressure in the chamber above the diaphragm plus the bias
spring. The valve spring then closes the supply valve and a new balance point is reached
until a humidity change upsets it. Because of the bias spring, the minimum control pressure
is about 1/2 psig.
Direct Acting Here the basic sensing and lever movement is the same as described above. See Figure 4.
However, the nozzle is in a different location; it's on the opposite side of the nozzle lever.
Thus a decrease in humidity results in the flapper pulling away from the nozzle and
decreasing the control pressure.
The element and nozzle levers pivot on flexure pivots to minimize hysteresis. A bimetal link
on the element lever compensates for ambient temperature changes.
Figure 4. Hygrostat Operation.
Calibration The hygrostat is factory calibrated to pass a control pressure of 9 + 4 psig at approximately
40% rh. The factory sensitivity setting is centered to give approximately 2 psig per 1% rh.
Item numbers shown in parentheses are called out in Figure 5.

Technical Instructions HU 186 Room and Duct Hygrostats
Document Number 155-027P25
February 14, 2005
Page 4 Siemens Industry, Inc.
Calibration,
continued
Room Type
1. Remove the cover using the calibration tool.
2. Loosen the test screw (2) 1/2 turn. Slide the rubber tubing of a pressure gauge over
the test port to measure the control pressure.
3. Measure the relative humidity near the hygrostat. See the Use of Psychrometric
Chart section.
4. If the room humidity is higher than desired, use the calibration tool to turn the
adjustment screw (1) counterclockwise to lower the humidity. A 1/4 turn of the
adjustment screw will change the set point about 10% rh
5. Cam post (4) is a coarse adjustment and should only be used if the desired set point
cannot be obtained by the adjustment in Step 4. It is primarily a factory adjustment to
obtain a parallel relationship between the nozzle lever (7) and the element lever (6).
Duct Type
1. Connect pressure gauge to control connection on duct box.
2. Measure relative humidity in duct.
3. Remove cap plug on duct cover and insert calibration tool to make adjustments given
in Step 4 above. See Figure 6.
4. Replace cap plug.
Figure 5. Hygrostat Assembly.
Figure 6. Hygrostat Calibration.
Sensitivity
Adjustment Item numbers shown in parentheses are called out in Figure 5.
1. Carefully loosen sensitivity adjustment (8) using a 3/16-inch wrench.
2. Slide the sensitivity adjustment (8) to desired position on the element lever (6).
Sensitivity will be 4 psi per 1% rh at the end nearest the element, down to 1/4 psi per 1%
rh at the end attached to the flexure pivot. See Figure 4. An overtravel spring on the
sensitivity adjustment assembly prevents damage to the nozzle on a reverse acting
hygrostat.
NOTE: When the sensitivity is changed, the element must be recalibrated for set
point.

HU 186 Room and Duct Hygrostats Technical Instructions
Document Number 155-027P25
February 14, 2005
Siemens Industry, Inc. Page 5
Use of
Psychrometric
Chart
A sling psychrometer is probably the most readily available humidity measuring device.
Plotting the wet and dry bulb temperature readings from it on a psychrometric chart
determines the relative humidity.
As an example, assume a dry bulb temperature of 70°F, and a wet bulb temperature of
53°F, measured with a sling psychrometer. Using the psychrometric chart illustrated in
Figure 7, follow the 70° dry bulb temperature line vertically until it intersects the 53°F wet
bulb temperature line. This determines the relative humidity point. In this case, the 30%
relative humidity line goes through the point; therefore, the relative humidity is 30%.
Figure 7. Psychrometric Chart.
Installation
Room Type
See Technical Bulletin 155-210P25 (TB-145) for instructions covering terminal
roughing-in through the wall plate stage. HU 186 plugs into the terminal connector
through two holes in the wall plate. When facing the wall, the supply connection will be on
the left for a horizontal installation and on the bottom for a vertical installation. Two
captive mounting screws fasten the hygrostat body assembly to the wall plate. The cover
is held in place by two button head cover screws which are tightened with the calibration
tool. Wall Plate Kit No. 180-443 is included with the room hygrostat.
Duct Type Cut an opening in the air duct. See Figure 10 for dimensions. Fasten the duct box flange
to the duct using four No. 8 sheet metal screws.
Maintenance Item numbers in parentheses are called out in Figure 8 and Table 2. Clean the
membrane element (13) with a soft, dry brush when dirt or dust accumulates. The
hygrostat should not be totally disassembled in the field. The only parts which should be
replaced are items (5) through (7), (10) through (13), and (16) in Table 2 and Figure 8.
As an initial check, make certain that there is 15 to 25 psig of clean, dry supply air. Use
a pressure gauge and rubber tubing to measure control pressure at the test screw (15).

Technical Instructions HU 186 Room and Duct Hygrostats
Document Number 155-027P25
February 14, 2005
Page 6 Siemens Industry, Inc.
Troubleshooting
Control Pressure
Remains at 1/2 psig
Troubleshooting contains the most common problems and solutions.
1. Remove the cover and connect a pressure gauge.
2. Gently press the nozzle lever against nozzle. The control pressure should increase. If
not, the restrictor hole in the restrictor plate (6) is clogged.
3. Replace the restrictor plate using the replacement parts in the Restrictor Plate Kit.
See Table 2.
4. Remove the old gaskets (5 and 7) and restrictor plate (6). Reassemble with the new
kit parts, putting them in the same relative positions as the original parts. Make sure
that the gasket connecting the two holes is between the restrictor plate and the
cover.
Control Pressure
Remains at Maximum
(15—25 psig)
1. Gently push the nozzle lever (2) away from nozzle (17).
2. If the control pressure does not drop to approximately 1/2 psig, check for a clogged
nozzle.
3. Carefully clean the tip of the nozzle. Also clean the nozzle lever where it contacts the
nozzle, as dirt will accumulate and clog the nozzle opening.
Excessive Air Leakage
from Nozzle-Control
Pressure Does Not
Drop
1. If excessive air leakage occurs and the control pressure does not drop to 1/2 psig
when the nozzle lever is pulled away from the nozzle, then there is dirt on one of the
relay ball valves. See Figure 4 in the Operation section.
2. The dirt particle on either the supply or the exhaust balls can usually be removed by
moving the lever so that it alternately opens and closes the nozzle. This fluttering
action will usually dislodge dirt from the ball valves.
3. Disassembly of the body (19) and base (20) to access the relay is not recommended.
Replacement of
Membrane Element 1. If the membrane element (13) is damaged and becomes cracked or torn, replace it
with parts in the Membrane Element Kit. See Table 2.
2. Disconnect the old element by removing screws (12) and (16).
3. Attach the new element.
4. Recalibrate using the procedure in the Calibration section.

HU 186 Room and Duct Hygrostats Technical Instructions
Document Number 155-027P25
February 14, 2005
Siemens Industry, Inc. Page 7
Hygrostat
Components
Figure 8. Hygrostat Construction.
Table 2. Parts List for Hygrostat (Item Numbers See Figure 8).
Item
Part
No.
Part Name
Qty.
Material
Item
Part
No.
Part Name
Qty.
Material
I - Adjusting Screw 1 Brass 13 See 24 Membrane Element
Assembly 1 -
2 - Nozzle Lever 1 Stainless
Steel 14 - Cam Post 1 Brass with Teflon®
3 - Sensitivity Adj.
Assem. (RA)
Sensitivity Screw
(DA)
1 - 15 833-009 Test Screw 1 Bronze
4 - Restrictor Cover 1 Brass 16 See 24 Long Element Screw - Brass
5 See 23 Upper Gasket 1 Neoprene 17 186-162 Nozzle Assembly
Nozzle Assem. Mod 5
to 7
1
1 Brass Brass
6 See 23 Restrictor Plate 1 Brass 18 - Cover Screw 2 Stainless
Steel
7 See 23 Lower Gasket 1 Neoprene 19 - Body Assembly - -
8 - Restrictor Cover
Screws 2 Brass 20 - Base - -
9 - Element Lever
Assembly 1 - 21 - Lockwasher No. 8 1 Steel
10 See 24 2-56 Hex Nut I Brass 22 - Adjustment Screw
Spring 1 Bronze
11 See 24 Lock Washer I Steel 23 180-893 Restrictor Plate Kit - Incl. Items
5, 6, 7
12 See 24 Short Element
Screw 1 Brass 24 186-062 Membrane Element Kit - Incl. Items 10, 11,12,
13, 16

Technical Instructions HU 186 Room and Duct Hygrostats
Document Number 155-027P25
February 14, 2005
Information in this publication is based on current specifications. The company reserves the right to make changes in specifications and models as
design improvements are introduced. POWERS is a registered trademark of Siemens Industry, Inc. Product or company names mentioned herein
may be the trademarks of their respective owners. © 2005 Siemens Industry, Inc.
Siemens Industry, Inc.
Building Technologies Division
1000 Deerfield Parkway
Buffalo Grove, IL 60089
+ 1 847-215-1000
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Document No. 155-027P25
Printed in the U.S.A.
Page 8
Dimensions
Figure 9. Room Hygrostat Dimensions.
Figure 10. Duct Hygrostat Dimensions.