Honeywell HM700A1000, Installation Instructions Manual

HM700A1000

3

33-00118—01

How the Humidifier Works

The HM700 is an atmospheric steam generator that uses heat 

generated by electrical current flowing between submerged 

electrodes to generate steam. The HM700 is designed for on-

demand air humidification via a steam distributor.

STEAM GENERATION

• Once the unit receives a demand signal and the safety loop 

between terminal 1 and 2 is closed, the humidifier closes 

the contactor and measures the electrical current.

• If the demand is lower than the actual output the inlet valve 

is kept closed and output is reduced by letting the water 

level in the cylinder decrease by evaporation.

• If demand is higher than the actual output, after a brief 

delay the fill valve is activated and water flows into the fill 

cup. Water from the fill cup flows into the bottom of the 

cylinder through a hose connected to the drain valve 

housing.

NOTE: The cylinder is gravity fed from the fill cup. If 

backpressure from the steam line is too high it 

will cause water to back up in the fill cup and 

flow down the overflow line to the drain.

• As soon as the water in the cylinder comes in contact with 

the energized electrodes, current flows through the water. 

The resistance of the water to the electrical charge 

generates heat and in turn steam. The electrical current 

(and steam output) increases as the level of water 

increases, as more of the electrode becomes submerged. 

The unit continues to fill until the current matches demand 

or the high water sensor detects a high water level.

• The HM700 repeats the fill and boil down cycle repeatedly 

to match output to demand.

• Over time minerals in the water will adhere to the cylinder 

electrodes. The humidifier will automatically fill to a higher 

water level to maintain full capacity during the life of the 

cylinder. Eventually because of scale formation it will no 

longer be possible for the humidifier to reach its full 

capacity. The HM700 software monitors this condition and, 

when detected, will stop operating and flash the yellow 

LED in a repeating sequence of 4 flashes.

DRAINS

• As steam is produced, minerals are left behind, increasing 

the conductivity of the water. The HM700 patented auto 

adaptive cycle will monitor the water conductivity and 

perform drains to maintain the water at optimal conductivity 

for peak performance.

• The auto adaptive cycle ensures cylinder life is maximized. 

It does this by keeping the tightest control and most 

efficient use of water during the entire cylinder life.

STEAM DISTRIBUTION

Steam generated by the humidifier may be introduced into the 

air in several different ways. The most common method for 

adding the steam into the air is to mount a steam distributor 

tube in a supply air duct.

STEAM LINE

The steam line between the cylinder steam outlet and the 

distributor serves two purposes: it is used as a conduit to 

transfer the atmospheric steam from the humidifier to the 

distributor, as well as providing a means to remove 

condensate. See “Steam Lines and Condensate Return 

Instructions” on page 8 for information on selecting steam 

lines.

CONDENSATE RETURN

Whenever steam is distributed condensate is formed in the 

distribution system. Insulating steam lines is one important 

way to reduce the amount of condensate formed. Steam lines 

are sloped so that condensate does not collect in the lines and 

create a restriction to steam flow. The condensate must be 

collected and removed from the system so that it does not 

build up and leak into the duct. Condensate can be returned to 

the HM700 fill cup to reduce water waste or can be fed to 

drain.