Honeywell H1008 Automatic Humidity Control with HumidiCalc+ Software Copyright © 1998 Honeywell Inc. • All Rights Reserved Rev 1.
Automatic Humidity Control The Honeywell H1008 Automatic Humidity Control with HumidiCalc+ Software is the world’s most advanced stand-alone humidity control. Simple to install, easy to troubleshoot, it is designed to save the installing contractor time, while maximizing benefits to the homeowner.
Defining a Comfortable Humidity Level Much research has been conducted on what combination of temperature and humidity creates the most comfortable indoor environment. The 1997 ASHRAE Fundamentals Handbook1 defines how comfort is perceived as a function of temperature and humidity. Figure 2 shows a summary of the ASHRAE conclusions.
The message to take away from all this is: If you are in the business of trying to provide a comfortable indoor environment, controlling a humidifier by sensing relative humidity may not result in optimum control. Especially poor performance may result when the temperature in the living space experiences large swings, like in instances where setback thermostats are used. In these applications, a humidity control that controls based on dewpoint will result in optimum control over all conditions.
Figure 3 illustrates why condensation occurs: Inside = 70 F Window Panes Window = 40 Outside = 0 F Figure 3 – Temperature Profile of Double Pane Window Figure 3 shows the temperature profile through a typical double pane window. If it is 70 F inside and 0 F outside, depending on the insulating value of the window, the temperature at the window surface may be around 40 F.
Outdoor Temperature Compensating Humidity Controls Honeywell, with the Perfect Climate Comfort Center , was the first to introduce an electronic humidity control system for the residential market designed to automatically adjust humidity levels based on outdoor temperature. This system also considers the effect of indoor temperature in its algorithm, providing optimum control for all combinations of indoor and outdoor temperature.
The AutoTrac control does not have the ability to provide true dewpoint control. This may result in overhumidification at times when the temperature is greater than normal conditions and underhumidification if the temperature is less than normal conditions. For example, if during night setback the temperature was 60 F, if the AutoTrac were able to achieve its 45 %RH, the dewpoint would be 39 F. If the temperature were raised to 72 F during recovery, the relative humidity would only be 30 %.
H1008 Automatic Humidity Control with HumidiCalc+ - The Technical Approach We found that there is more than a casual relationship between furnace run time and outdoor temperature. In fact, in a single stage heating system, in steady state, the percentage of burner on-time (% on) is linearly related to the difference between the balance point (in this context, the temperature at which it is warm enough that the furnace never runs) and the outdoor temperature.
oversize). In this case the furnace will only be running 50% of the time at the ASHRAE design temperature of –16 F. Window Surface Temperature - deg F Next, we looked at the insulation values of windows, and found that naturally, there is a relationship between the temperature of the inside surface of the window and the outdoor and indoor temperatures. This was shown in Figure 2. Of course, all windows are different, but Figure 6 shows some nominal values for typical window types.
adjusting a single input value, we can achieve a control point that satisfied every one of the thousands of combinations of the variables. Voila . By adjusting a single knob setting we can provide a solution for the entire range of five input variables. Figure 7 shows the operational characteristics of the H1008 Automatic Humidity Control with HumidiCalc+ Software. 60.0 Maximum Allowable Dewpoint 50.0 Knob Setting = 1 40.0 Knob Setting = 2 30.0 Knob Setting = 3 20.
Nobody has more knowledge about heating loads than Honeywell, the world leader in temperature control. More furnaces are controlled by Honeywell thermostats than any other, so nobody understands the science of temperature control better than we do. In order for the prediction of outdoor temperature based on furnace cycling to work, we needed to develop an algorithm to filter out changes in heating load that are not the result of changes in outdoor temperature.
80 40 Room Temp. 70 35 60 30 Temp. Setpoint Window Temp. 25 40 20 30 Dewpoint 20 15 10 Digitial Output o Temperature ( F) 50 Outdoor Temp.
80 40 70 Indoor Temp. 35 60 30 Temp. Setpoint Window Temp. 25 40 20 30 Dewpoint 20 15 Outdoor Temp. 10 10 0 Furnace Cycles Humidifier Cycles 5 -10 0 -20 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Time (hrs) Figure 9 – H1008 Automatic Humidity Control Hardware Closed Loop Run Figure 9 is the identical case, with the actual H1008 hardware and software in control of the simulated humidifier.
80 40 Room Temp. 70 35 60 Window Temp. Temp. Setpoint 30 25 40 20 Dewpoint 30 20 15 Digitial Output o Temperature ( F) 50 Outdoor Temp. 10 10 0 Humidifier Cycles Fan Cycles (G) Furnace Cycles (W) 5 -10 24:00:00 23:00:00 22:00:00 21:00:00 20:00:00 19:00:00 18:00:00 17:00:00.0 16:00:00 15:00:00 14:00:00.0 13:00:00 12:00:00 11:00:00 10:00:00 09:00:00 08:00:00 07:00:00.
Making the Best of a Duct Mounted Humidity Control One of the things we learned early on in this development was that a return air duct is not the best place to mount a humidistat that controls only by relative humidity. There are two major factors that can dramatically affect the accuracy of standard humidistats: 1. Ambient Temperature of the Equipment Room If the temperature in the area where the HVAC equipment is installed differs much from the living space temperature, errors in sensed RH can develop.
100 40 90 Room Temp. 30 70 60 25 50 Dewpoint 20 40 30 15 20 Duct RH 10 0 Humidifier Cycles 10 Fan Cycles (G) 5 Furnace Cycles (W) -10 14:00:00.0 13:30:00 13:00:00 12:30:00.0 12:00:00 11:30:00 11:00:00 10:30:00 10:00:00 09:30:00 09:00:00 08:30:00.
2. Humidity Control Located Too Close to Bypass Duct A second problem that can occur in many installations is a result of the humidity control being located too close to the bypass duct. We always recommend mounting the humidity control as far upstream from the bypass duct as possible (> 24” is desired). However, in many installations the desired separation is not possible, and compromises have to be made.
dewpoint increases slightly in response to the humidifier cycles. During this period the relative humidity sensed in the duct is as low as 13 %. Because the H1008 controls based on dewpoint, it is able to cycle intermittently during the temperature recovery period when the relative humidity is artificially low. This ensures that the dewpoint is maintained dewpoint below the window temperature. Figure 13 shows additional field test data taken the following night at the same site.
While the humidifier was on during the entire recovery period starting at 4:15 a.m., the sensed RH ranged from 20 to 30 %. The continuous operation of the humidifier caused the dewpoint in the house to exceed the window temperature for over two hours. Contrast this performance with the performance of the Honeywell H1008, shown in Figure 12, where the dewpoint in the house never exceeded the window temperature.
a ¾” diameter hole to be cut in the duct. Drilling this hole with a uni-bit is a snap. Simply drill the hole, place the control on the duct, and secure it with selftapping screws. Figure 14 – H1008 Sensors This method of mounting greatly improves the sealing of the return air duct. Building inspectors sometimes require leaks around the rectangular cutouts to be sealed by caulking. 3.
Logic to determine if the fan is running is determined from the equipment inputs so a current sensing relay is never required, providing additional savings to the contractor on jobs that would normally require one. 4. Automatic Configuration and Diagnostics Unlike AutoTrac , the H1008 does not require a jumper selection if the control is installed with either a bypass or powered flow through humidifier. The H1008 also automatically detects whether or not the outdoor sensor is installed.
Direct Comparison Chart – Honeywell H1008 Automatic Humidity Control with HumidiCalc+ Software vs. AutoTrac AutoTrac Honeywell H1008 Installation Outdoor Sensor Not required for single stage furnaces. Recommended for heat pumps and multi-stage furnaces. Mounting ¾” diameter hole for inserting sensors into return air duct. Wiring Large screw terminals provided for wiring. Determining fan operation automatically detected by control logic.
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