Recommended Standard Refrigerant Sizing
 
The Diamond DH equipment has incoming air cross over the evaporator coils followed by crossing over the reheat coils and then is exhausted to the air/tank, etc. In this manner, the water is removed from the air which in turn is reheated to cause the relative humidity to be reduced even further.
 
When our system is in the:
Full DH Mode - the exhausted air will be approximately 5 to 35 °F above ambient.
A/C Mode - temperature will be in the range of 15 to 30 °F above ambient.
Heat Mode - temperature will be 30 to 50 °F above the ambient temperature.
 
The difference between a modified DH system and full DH is both temperature and humidity control. The temperature difference is approximately 5 to 25 °F cooler. Depending upon the mode the relative humidity will be in the 30% - 50% range.
 
Sizing DH Units
 
Assume a tank size of (a) 90 feet in diameter with a 7 foot floating roof and (b) 100 feet in diameter and 40 feet tall. To determine the volume of the tanks, use the formula:
 
  Volume = 3.14 (radius)(radius)(height)
                 For the floater, Volume = 3.14(45)(45)(7) = 44,509 cu. ft.
                 For the total tank, Volume = 3.14(50)(50)(40) = 314,000 cu. ft.
 
             CFM size = Volume (60) = Volume
                                 4                 15
 
In the case of the two above examples, the DH sizing would be
 
For the floater, CFM = 44,509 = 2,967 CFM = 1 x 3000 unit
              15
 
For the total tank, CFM = 314,000 = 20.993 CFM = 3x7000 units + 1x3000 unit
               15
 
Flexible duct used for each size machine
For the 1000 – 3500 CFM units - 14 inch diameter
For the 5000 CFM units - 16 inch diameter
For the 7000 – 10000 CFM units - 20 inch diameter
 
Keep the length of the duct to a minimum for two reasons:
  1. Due to internal friction caused by the air flowing through the duct, you will lose CFM going into the tank, and
  2. The air within the duct is subjected to the ambient air temperature and this in turn can affect the conditions of the air going into the tank.
However, should it be necessary to have duct lengths longer than 100 feet (less if the duct is vertical), a blower should be inserted in the line to “boost” the CFM. Match the blower as closely as possible to the CFM of the DH unit.
 
As an alternative, if possible, consider the use of longer power cable instead of the duct. It is cheaper for the customer and a better solution for the performance of the DH unit.
 
The duct should be evenly spaced around the circumference of the tank as possible. It should also be placed within the tank so that you receive (a) better air distribution within the tank, and (b) it is not pulled out of the tank by mistake.
 
With four air exchanges per hour being the basis of our sizing the DH unit, there should be enough air flow. However, some contractors “just like” to have auxiliary blowers to help exhaust the air and “assist” the DH. A Coppus fan would be a typical example. This should, however, be matched as closely as possible with the total DH CFM. For example, should you place a 10,000 CFM blower on a tank using a 4,000 CFM DH unit, you will pull an additional untreated 6,000 CFM of outside air into the tank. This will negatively affect the performance of the DH
 
Heaters
 
There are two cases where a heater should be used:
  1. When the ambient air is so cold that the increase in temperature caused by the unit operating in either the full DH or heat mode is not satisfactory to obtain the desired air temperature with the tank. However, note that this is air temperature, not surface of skin temperature. SKIN TEMPERATURE CANNOT BE GUARANTEED unless you have an insulated tank and even then one must be cautious.
  2. When additional heat is required to help “flash off” the solvents to assist in the intermediate drying of the lining. Again, do not make any promises regarding a time/cure relationship without an insulated tank since this, too, deals with skin temperature.
The heaters are generally matched to the CFM flow of the DH unit. Any variation will either increase or decrease the temperature obtained. For example, if you place a 60KW heater in line with a 2,000 CFM unit, you might burn out the heater because the air flow is too slow. By the same token, if you place a 15KW heater in line with an 8,000 CFM unit, the air flow will be so fast that you will receive very little heat increase.
 
As a rule of thumb, if the heaters are properly sized, the increase in temperature provided by the heater will equal 1.0 – 1.25 times the KW. For example, a 15KW heater can provide a temperature increase of 15 – 20 °F to the air.
 
There are two formulas to relate KW of the heater to power and heat:
  1. KW x 1.2 = Amps required to power the heater with 480 volt, 3 phase power.
  2. KW x 3.4 = BTU of heat supplied by the heater in question.