Cooling as required – Diesel Progress International Winter Edition


Julian Buckley – Editor at Diesel Progress International and New Power Progress speaks with Transtherm’s Tim Bound about fan-based gen set cooling

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“When we first started the business over three decades ago we would to sell anything to anybody,” says Tim Bound, director of Group Sales and Marketing at Transtherm. “But we realised that was a flawed business model. We decided to sell only what we were manufacturing, the air blast coolers of different types, the dry coolers, adiabatic coolers, free coolers, together with pump sets.”
Having successfully narrowed down the company product portfolio, Coventry-based Transtherm now supplies closed-circuit, remote-mounted flatbed coolers, which can be mounted either horizontally or vertically to suit the application, and V-coolers. The company delivers to OEMs and dealers (who create packaged solutions), and to various industries, including pharmaceuticals, food and beverage, and aerospace. Unusually – but with unspoken necessity – the company also works with cremation firms.
The company has done a lot of recent work delivering cooling solutions for gen sets used at data centres. These installations use a colossal amount of power, usually taken directly from the grid; such is the power draw that they would sometimes need a dedicated substation. The grid supply would have been backed up with diesel gen sets, but Bound says that there has been a move to gas-fired gen sets as a primary energy source to take advantage of the efficiency and environmental potential.
“The installation might have 10 gen sets as the main power source. Depending on the set up, that would require anywhere from one to a full 10 units as backup. Then those are backed up by the grid. Using the gen sets can fulfil related stipulations for using renewable energy, so it’s attractive to the customer. In all areas, we’re getting switched on to being green,” he says.

Cooling solutions

Transtherm is a specialist in manufacturer of gen set coolers and pump sets. The company can package that hardware with a control system which is prewired and preprogramed to customer specifications. If a pump set is also being delivered, the system can be set up to use a single control panel.
“The idea is single lift, single power supply and single water connection,” says Bound.
The type of gen set being used will define the cooling set up, whether that’s a single, double or triple bank cooler. Bound explains more: “In areas where the grid is a bit weak, a gas-fired gen set could be used to support the power supply. In that instance all that matters is the power, it’s a boost. They’re not taking advantage of the heat, it’s really just a safety net. So a double-bank cooler is fine.”
Switching to a combined heat and power (CHP) installation can require a modified set up, says Bound. “If the jacket water heat is being recovered and put to use, there won’t be any heat going jacket water heat exchange coil in the cooler. However, if we’re still dragging air across those coils in order to cool the inter-cooler circuit, it will be massively overcooling the jacket circuit. In cases like this it’s preferable to go to two single-bank coolers with completely independent controls.”
Essentially, the best solutions deliver cooling as cooling is required. This is particularly important when dealing with larger gen sets, where net electrical output should be as high as possible with minimal parasitic draw from the cooling fans. To reduce this effect, Transtherm has been exclusively using variable-speed fans for many years.
Bound says that variable-speed fans offer a series of benefits, including the ability to speed up and down independently or as a unit. He says that power draw is relative to the cube of its speed. To put this in perspective, if traditional fixed speed fans were being used and half of the them were being run at full speed the power draw is 50%.
“However, when using variable speed fans all of them would be operating at circa. 50%. If we cube 50%, that’s 12.5% power usage. In cases of fixed speed fans that are on a stage control, 50% of the area won’t be getting any direct cooling, it’s redundant and an efficiency reduction. Drawing half of the air over the whole coil is much more efficient, meaning we can operate the variable speed fans at circa. 45% rather than 50% to get the same cooling effect.”

Load profile

Bound says that the company uses other data to develop the most efficient cooling system. Such factors as local weather, with a particular focus on low and high temperatures, are factored into the figures, to determine power draw at each degree of ambient air temperature. Those are multiplied by the frequency of ambient temperature to return an annual power consumption profile.

He says that the difference in load profile between fixed and variable fans is “staggering”. And although Transtherm might not offer the cheapest solutions, Bound says that the company wins a considerable amount of business by delivering basic operational value.

“Depending on the tech, we will either look at the ROI in terms of how long it will take to pay off the difference in cost between our solution and a competitor, or in some cases we will just outline how long it will take to pay off the entire cost of our equipment. Often, that can be less than a year,” he says.

The hardware supplied by Transtherm also supports flexibility in terms of gen set location, particularly when looking at diesel installations. Focusing on external remote cooling, the hardware can make or break plans to locate a unit within a limited space.

“If a gen set has to go into a basement in central London because there’s no other space, an engine-mounted radiator won’t work. Instead, our coolers can be put on the building roof,” says Bound.

In other cases, when mounted on the gen set container roof, space comes at a premium. If the gen set has a lot of hardware at one end, Transtherm can supply V coolers (single or double bank), which offer a much greater cooling density, allowing for a smaller footprint. These are of particular interest when there are fixed boundaries (walls, etc.) around the gen set.

Awkward site locations could see the external air temperatures increase by as much as 10°C above ambient conditions and this information should be used when calculating cooler size.

Noise is another factor which can be added into the calculations. “There’s no machine we make which requires ear defenders,” says Bound. “The quietest equipment is no louder than room air conditioning, you might need a visual check to see if the machine is running.”

But he points out that while the faster the fans spin, the greater the amount of air they can move, this also means they have to use a reduced amount of heat exchanger surface material.

“There are a heap of factors determining how much heat you can remove, but the main two are material quantity and volume of air. Reduce the amount of air, you must increase the amount of metal. Some engine applications have a daytime and night-time noise requirements and that’s another advantage of variable-speed fans, lower noise at reduced speeds – the noise drop off as the fan speed goes down is significant.”

More often than not, fan speed is adjusted automatically to suit coolant and air temperatures as measured by the onboard systems. The systems are now advanced to the point where if there is an issue, engineers can remotely interact with the cooling systems to find out what’s needed to fix the problem. It cuts down on man hours and on machine downtime.

The biggest factor in successful cooling, says Bound, is getting the correct ratio of air flow and heat exchange material. “Taking into account fan speeds, the heat exchange coil for the high-temperature circuit has to be sized correctly. If there’s not enough material, the engine will likely derate and possibly even trip.”

Pump sets

Any water-cooled system needs a pump set, as without the related water flow there is limited cooling effect. Compensating for pressure changes is critical to successful cooling, as Tim Bound explains: “We use pumps rated for flow and any pressure loss in the system. As water flows through the system, we need to allow for the cooler pressure drop, which is typically up to 1 bar, and the system pressure drop which is generally up to 6 bar.”

In some cases, the gen set will have its own built-in pumps. While these can reduce parasitic load, the generally low performance of these units requires a cooling system with a very low pressure drop. Alternatively, Transtherm can supply an external pump set which can offer higher performance, in turn allowing for higher pressure drop coolers that could save footprint and/or cost.

“Deciding which hardware to use comes under our consultative approach,” says Bound.

Engineers at Transtherm will help and advise customers as much as possible, using their knowledge and experience, but Bound says that as a critical company rule is to stop short of saying ‘yes’ when we should be saying ‘no’. “This could include the need for customers to use experts in computational fluid dynamics, modelling water and air flow if there are serious concerns of warm air recirculation.“