Pureheat Advantages in Underground Water Tank Restoration |
Project |
Provide clean, dry heat for restoration of Hydepark cell number four, a 50 million liter (13.2 million gallon) water tank in Ireland. |
| Contractor |
John Grahams, Dromore, Ireland |
Challenges |
Efficiently raise the temperature inside the underground potable water tank to 10° C (50° F) without emissions and ductwork, enabling contractors to have a choice of restorative coatings. |
WNCC Equipment |
Pureheat Hydronic Air and Surface Heater with HX60 Heat Xchangers™ |
Results |
In addition to more efficiently heating the tank with dry, recycled air, the study finds that fuel savings by using Pureheat vs. an air heater to be approximately £565 ($1,020) per 72 hours of use. |
 Contractors on multiple continents are employing the versatile Pureheat Hydronic Air and Surface Heater for underground water tank restoration applications. Using liquid-to-air exchangers, Pureheat is the most efficient and cost-effective method for bringing emissions-free, dry air to the workspace.
As an air heater, the unit delivers up to 252 kW (860,000 BTU/hr) fuel input with an 83% heater efficiency to quickly deliver heat to large spaces, such as underground water tanks. With its self-contained heating system, the Pureheat unit supplies a heated glycol fluid via hoses to each heat exchanger from outside the structure, providing heat without introducing open flame or combustion by-products into the workspace.
Placed throughout an enclosed workspace, each heat exchanger’s fan draws cooler air from the area and blows it across heated coils to produce hot, dry and clean air. The fluid then cycles back to the main unit via a return hose for reheating. In its standard configuration, Pureheat is equipped with either 16 HX15 or 4 XH60 Heat Xchangers™, supplying up to 15 kW (51,216 BTU/hr or 60 kW (204,865 BTU/hr) respectively. Used as an air heater, it heats areas as large as 50,000 m3 (1,765,733 ft3) workspaces.
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Increased Efficiencies in Ireland
Wacker Neuson recently worked with a contractor in Ireland to analyze the most-efficient heating system for restoring an underground 50-million-liter (13.2-million-gallon) potable water tank. The customer had considered using indirect-fired air heaters to heat the 50,400 m3 (1.78 million ft3) non-insulated workspace, but was also interested in using the liquid-to-air heat capabilities of the Pureheat heating system.
One reason for the Pureheat interest: heating capabilities. For underwater storage tanks, two coatings are frequently used in Ireland for the restoration process. One coating cures at 5° C (41° F), while the other at 10° C (50° F). While the latter is the coating of preference, most contractors chose the former due to the limited access to underground tanks and heating inefficiencies of traditional air heaters. Most tanks simply cannot be bought up to the required 10° C (50° F) curing temperature for a long enough time period to effectively use the preferred coating.
 If Pureheat effectively and consistently heats the inside of the underground tank to the desired temperature, the contractor can apply the preferred compound while adhering to a strict timescale. This will also help the customer secure future business.
In comparing traditional air heater approach against Pureheat, the immediate noticeable advantages for the liquid-to-air heating system are access and efficiency. Pureheat requires only eight, 5.1-cm (2-in) holes drilled in the roof for supplying heated glycol to the heat exchangers. To get the equivalent heating capacity with air heaters, crews would need to insert 10, 30.5-cm (12-in) hot air ducts into the tank, affecting tank entry and requiring extensive repair after restoration is complete.
Since air heaters must be positioned outside the tank, ducting is necessary to direct heated outside air into the tank. While it generally accepted that ducting reduces efficiency by as much as 30%, this figure increases for longer duct runs and more angles created by direction changes. Depending on outside duct length and ambient temperatures, insulations blankets may also be required to improve air heating, which leads to increased labor and material costs.
Air heaters continually draw cool, moisture-laden outside air requiring a substantial amount of energy to raise the temperature inside the tank. By contrast, Pureheat works by continually reheating the air from inside the workspace. Each Wacker Neuson Heat Xchanger is thermostatically controlled, so the exchanger will cycle on and off to maintain desired temperatures inside the workspace. Unlike air heaters, Pureheat is designed to operate without constant supervision, so the unit quickly brings and consistently keeps the workspace temperatures above 10° C (50° F) while working more fuel efficiently and cost-effectively for the duration of the job.
Heating recycled air from within the workspace also produces a drying effect inside the tank, which proves most beneficial as crew members apply the tank sealer. Contrary to the moist outside air drawn in by air heaters, which can leave pools of water on the floor and the tank too damp at start up to apply the sealer, the dry air of Pureheat allows crews to focus on applying the sealer 24 hours a day. This reduces labor downtime and the need to mop up excess water as a result of using air heaters.
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Significant Fuel Savings
The following analysis compares similar heating capacities of the Pureheat liquid-to-air heating system against indirect-fired air heaters. Since Pureheat is equipped with four XH60, 60 kW (204,865 BTU/hr) Heat Xchangers for the Hydepark application, the comparison is drawn with a 60 kW air heater.
 The time it takes to bring the underground water tank to desired temperatures for applying the preferred sealer depends on ambient conditions, but for this side-by-side comparison, a time period of 72 hours is being used. While Pureheat offers the advantage of thermostatic temperature control for unit cycling to reduce fuel consumption, this estimate assumes continual running for simplicity. The below calculations are based on a diesel fuel (Red Dyed – mobile off-highway) cost of £0.50 per litre.
Pureheat draws 8.5 Amps at 220 Volts, which results in a power requirement of 1870 Watts. Each of the four heat exchangers draws 4.6 Amps at 110 Volts, which equals 506 Watts per unit or 2,024 Watts total. With a total power requirement of 3,894 Watts, the recommended generator size for complete system operation is 7.5 kVA to accommodate additional onsite power needs.
The cost for running the Pureheat unit and heat exchangers are as follows:
- Pureheat heater: 20 liters/hr x 72 hours = 1,440 liters
- 7.5 kVA generator @ 60% load: 1.5 liters/hr x 72 hours = 108 liters
- Total fuel requirements: 1,440 + 108 liters = 1,548 liters
- Total fuel costs: 1,548 x £0.50 per liter = £774.00
Pureheat and the four heat exchangers transfer 240 kW (819,462 BTU/hr) of heat directly into the tank. However, the 60 kW (204,865 BTU/hr) air heaters contain diesel and other contaminants and emit noxious fumes as part of the exhaust, so they must be positioned outside the tanks. Therefore, these heaters require ductwork to transfer heat to the tank. In order to adjust for ducting heat losses, five air heaters would be required for the Hydepark application.
Each indirect heater produces 60 kW heat without ducting. Power consumption per heater is 1,650 Watts, so for five the total power need is 8,250 Watts. This requires a 10.25 KVA generator for system operation.
Summary of costs for air heaters is as follows:
- 60 kW heater fuel consumption: 6.98 liters x 5 = 34.9 liters/hr
- Total heater fuel consumption: 34.9 x 72 hours = 2,512.8 liters
- 10.25 kVA generator fuel consumption: 2.3 liters/hr x 72 hours = 165.6 liters
- Total fuel requirements: 2,512.8 + 165.6 liters = 2,678.4
- Total fuel costs: 2,678.4 x £0.50 per liter = £1339.20
With the Pureheat solution requiring 21.5 liters/hr of fuel vs. the air heaters’ 37.2 liters/hr, Pureheat delivers a per-hour fuel savings of £7.85 when calculating a £0.50-per-liter fuel cost. The contractor realizes £565.2 in fuel savings during the 72-hour run time by using the 40% more fuel-efficient Pureheat system. Additionally, unlike with Pureheat, fuel consumption with the indirect heaters will not drop as the underground tank reaches desired restoration temperatures, since cool and moist ambient air is continually being pulled from outside the tank.
The contractor could also achieve significant labor savings with Pureheat. This system is designed to operate all day and night without supervision, so the tank would maintain desired temperatures for sealant application 24 hours a day. There could be an issue with running multiple indirect heaters overnight and unattended.
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