Heat pump water heaters (HPWHs) are primarily designed for efficient water heating, but they also have a secondary effect of dehumidification. This dual functionality has led to questions about their effectiveness as dehumidifiers. While HPWHs can remove some moisture from the air, their dehumidification capacity is limited compared to dedicated dehumidifiers. This article explores the efficiency, performance, and practical considerations of using a heat pump water heater as a dehumidifier.
How Does a Heat Pump Water Heater Remove Moisture?
Heat pump water heaters operate on a refrigeration cycle, extracting heat from the surrounding air to warm the water in the tank. During this process, the evaporator coil cools the air, causing moisture to condense and collect. This incidental dehumidification occurs as a byproduct of the water heating function.
What is the Dehumidification Efficiency of Heat Pump Water Heaters?
The dehumidification efficiency of HPWHs is generally low compared to dedicated dehumidifiers:
- Summer performance: Approximately 0.9 pints per day (0.018 liters/hour)
- Winter performance: About 0.2 pints per day (0.004 liters/hour)
- High humidity conditions: Up to 1.3 pints per day (0.026 liters/hour)
In contrast, dedicated dehumidifiers can remove up to 35 pints (16.5 liters) per day.
How Much Can a Heat Pump Water Heater Reduce Humidity?
The humidity reduction achieved by HPWHs is minimal:
- In well-sealed, moderately conditioned spaces, they may maintain relative humidity around 55% ±5% during moderate temperature days.
- In less controlled environments like garages, the impact on humidity levels is often negligible.
What Are the Quantifiable Benefits of Using a Heat Pump Water Heater for Dehumidification?
While HPWHs provide some dehumidification as a free byproduct of their operation, the benefits are limited:
| Aspect | HPWH | Dedicated Dehumidifier |
|---|---|---|
| Energy Consumption | Efficient for water heating, minimal for dehumidification | Higher, but more effective for moisture removal |
| Operational Time | ~5% of the day | Can run continuously |
| Moisture Removal | 0.2-1.3 pints/day | Up to 35 pints/day |
The primary savings from HPWHs come from efficient water heating rather than dehumidification.
Can Heat Pump Water Heaters Replace Dedicated Dehumidifiers?
In most cases, HPWHs cannot replace dedicated dehumidifiers due to their limited dehumidification capacity. Factors to consider include:
- Climate conditions
- Space size and layout
- Desired humidity levels
- Hot water demand
For effective moisture control, especially in humid environments, a dedicated dehumidifier is often necessary alongside an HPWH.
Are There Any Adjustments to Optimize Heat Pump Water Heaters for Dehumidification?
Unfortunately, there are no specific adjustments or settings to enhance the dehumidification capabilities of HPWHs. Their operation is primarily based on hot water demand, with dehumidification occurring as a side effect. Some models offer different operating modes (e.g., heat pump only, hybrid, electric only), but these do not significantly impact their moisture removal capacity.
What Are the Environmental Conditions for Optimal Dehumidification by Heat Pump Water Heaters?
HPWHs perform better in warm, humid environments, but their dehumidification effectiveness remains limited:
- Ideal conditions: Warm, humid spaces with high hot water usage
- Performance in basements: Can maintain moderate humidity levels in well-sealed areas
- Garage settings: Minimal impact on humidity levels
How Does the Energy Consumption of Heat Pump Water Heaters Compare to Dedicated Dehumidifiers?
- HPWHs: Energy-efficient for water heating, with coefficients of performance (COP) of 2 or greater
- Dedicated dehumidifiers: Consume 500-700 kWh per month in continuous operation
- HPWH dehumidification: Negligible additional energy consumption
While HPWHs are more energy-efficient overall, their dehumidification benefit is marginal compared to dedicated units.
In conclusion, while heat pump water heaters offer some dehumidification as a byproduct of their operation, they are not efficient replacements for dedicated dehumidifiers. Their primary value lies in energy-efficient water heating, with moisture removal being a minor secondary benefit. For effective humidity control, especially in challenging environments, a separate dehumidifier is often necessary.
References:
1. GreenBuildingAdvisor: Dehumidifying With Heat Pump Water Heaters
2. Fine Homebuilding: Dehumidifying With Heat-Pump Water Heaters
3. Purdue University: Fifteen Years of Dehumidification Results from Heat Pump Water Heaters
